Development of bacterial cellulose composites as an alternative to leather
Abstract
O couro é um material natural amplamente usado nas indústrias do têxtil e do calçado. No entanto, o seu processo produtivo juntamente com o processo de crescimento dos animais apresenta um elevado impacto ambiental e humano. Com os consumidores cada vez mais atentos às questões ambientais e de bem-estar animal, existe uma procura crescente por alternativas sustentáveis e sem crueldade animal. Este trabalho visou o desenvolvimento de compósitos de celulose bacteriana (CB), como material estruturante, e óleos vegetais ativados e outros polímeros hidrofóbicos, como agentes flexibilizantes e hidrofobizantes, como um produto alternativo ao couro. Para isto, foi testada uma nova abordagem para a modificação da CB, combinando simplicidade, potencial para aplicação à grande escala e baixo custo, com base no uso de um processo simples de esgotamento para a incorporação dos polímeros na matriz da CB. Todas as combinações resultaram em compósitos hidrofóbicos (ângulo de contato máximo de 138°). Primeiramente foram usados dois polímeros comerciais hidrofóbicos da indústria têxtil, um amaciador à base de polidimetilsiloxano (PDMS) e um hidrofobizante à base de perfluorocarbono (PFC). Os compósitos obtidos eram respiráveis (permeabilidade ao vapor de água máxima de 373 g·m−2·24 h−1) e com performance satisfatória relativamente às propriedades mecânicas (força de rotura máxima de 48.4 MPa). Para aumentar o teor de base biológica no compósito, foi usado óleo de soja epoxidado acriloilado (AESO) numa mistura com um polímero à base de PDMS e polietilenoglicol (PEG) 400. Os compósitos de CB possuíam performances distintas, manipuláveis variando a percentagem de polímero. Posteriormente, foram desenvolvidos compósitos com a resina de AESO previamente emulsionada e em misturas com PDMS, PFC e PEG, resultando em compósitos termicamente estáveis (até 200 °C) e, globalmente, com propriedades mecânicas adequadas para a aplicação pretendida (força de rotura máxima de 35.9 MPa). Por fim, validou-se o desenvolvimento de compósitos usando um sistema redox ecológico para a polimerização do AESO, bem como o acabamento com um biocida e o tingimento dos compósitos. A associação de óleos vegetais ativados com membranas de CB constituiu uma abordagem inovadora e promissora para o desenvolvimento de um produto amigo do ambiente, quase exclusivamente composto de materiais biológicos e recicláveis, com potencial para aplicação nas indústrias do têxtil e do calçado, contribuindo para a redução da dependência do couro animal.
Full text
Marta Susana Machado Fernandes setembro de 2021 UMinho | 2021 Development of Bacterial Cellulose Composites as an Alternative to Leather Universidade do Minho Escola de Engenharia Marta Susana Machado Fernandes Development of Bacterial Cellulose Composites as an Alternative to Leather
setembro de 2021 Tese de Doutoramento Doutoramento em Engenharia Têxtil Trabalho efetuado sob a orientação de Professor Doutor António Pedro Garcia de Valadares Souto Doutor Fernando Octávio de Queirós Dourado Marta Susana Machado Fernandes Development of Bacterial Cellulose Composites as an Alternative to Leather Universidade do Minho Escola de Engenharia
ii DIREITOS DE AUTOR E CONDIÇÕES DE UTILIZAÇÃO DO TRABALHO POR TERCEIROS Este é um trabalho académico que pode ser utilizado por terceiros desde que respeitadas as regras e boas práticas internacionalmente aceites, no que concerne aos direitos de autor e direitos conexos. Assim, o presente trabalho pode ser utilizado nos termos previstos na licença abaixo indicada. Caso o utilizador necessite de permissão para poder fazer um uso do trabalho em condições não previstas no licenciamento indicado, deverá contactar o autor, através do RepositóriUM da Universidade do Minho. Licença concedida aos utilizadores deste trabalho Atribuição-NãoComercial-SemDerivações CC BY-NC-ND https://creativecommons.org/licenses/by-nc-nd/4.0/
iii ACKNOWLEDGEMENTS At the conclusion of the PhD, I would like to acknowledge to the people who supported me. I would like to start by expressing my gratitude to my supervisor and forever mentor Professor António Pedro Souto. He gave me the opportunity to join his research group in 2010 and his teaching expertise and enthusiasm for science allowed me to grow as a researcher throughout all these years. He was a great professor, a great person, and a friend. It was an honor to have him in my life. I am and always will be deeply thankful to him. I would like to deliver a word of appreciation and gratitude to my supervisor Doctor Fernando Dourado for all the support and guidance throughout this research work. Thank you very much for your advice and valuable suggestions. I would like to acknowledge Professor Miguel Gama for giving me the opportunity to participate in the Project “BUILD – Bacterial Cellulose Leather” and always support the progress of the work with his scientific knowledge. Finally, I would like to express my appreciation and thanks to all my colleagues for the moments we shared in the labs, Ângela, Vítor, Andrea, Isabel, Joaquim Jorge, Marta, Gonul, Ana Isabel, Xinyu, Lu’u, Derya, Sofia, Rui, Patrícia, Inês, Mónica. Thank you all. It was a great pleasure to work and learn from you. This project was supported by FEDER funding on the Programa Operacional Regional do Norte (NORTE2020) within the scope of the project NORTE-01-0247-FEDER-003435 (“BUILD–Bacterial Cellulose Leather”).
iv STATEMENT OF INTEGRITY I hereby declare having conducted this academic work with integrity. I confirm that I have not used plagiarism or any form of undue use of information or falsification of results along the process leading to its elaboration. I further declare that I have fully acknowledged the Code of Ethical Conduct of the University of Minho. University of Minho, September 13, 2021 Full name: Marta Susana Machado Fernandes Signature:
v Resumo Desenvolvimento de compósitos de celulose bacteriana como alternativa ao couro O couro é um material natural amplamente usado nas indústrias do têxtil e do calçado. No entanto, o seu processo produtivo juntamente com o processo de crescimento dos animais apresenta um elevado impacto ambiental e humano. Com os consumidores cada vez mais atentos às questões ambientais e de bem-estar animal, existe uma procura crescente por alternativas sustentáveis e sem crueldade animal. Este trabalho visou o desenvolvimento de compósitos de celulose bacteriana (CB), como material estruturante, e óleos vegetais ativados e outros polímeros hidrofóbicos, como agentes flexibilizantes e hidrofobizantes, como um produto alternativo ao couro. Para isto, foi testada uma nova abordagem para a modificação da CB, combinando simplicidade, potencial para aplicação à grande escala e baixo custo, com base no uso de um processo simples de esgotamento para a incorporação dos polímeros na matriz da CB. Todas as combinações resultaram em compósitos hidrofóbicos (ângulo de contato máximo de 138°). Primeiramente foram usados dois polímeros comerciais hidrofóbicos da indústria têxtil, um amaciador à base de polidimetilsiloxano (PDMS) e um hidrofobizante à base de perfluorocarbono (PFC). Os compósitos obtidos eram respiráveis (permeabilidade ao vapor de água máxima de 373 g·m−2·24 h−1) e com performance satisfatória relativamente às propriedades mecânicas (força de rotura máxima de 48.4 MPa). Para aumentar o teor de base biológica no compósito, foi usado óleo de soja epoxidado acriloilado (AESO) numa mistura com um polímero à base de PDMS e polietilenoglicol (PEG) 400. Os compósitos de CB possuíam performances distintas, manipuláveis variando a percentagem de polímero. Posteriormente, foram desenvolvidos compósitos com a resina de AESO previamente emulsionada e em misturas com PDMS, PFC e PEG, resultando em compósitos termicamente estáveis (até 200 °C) e, globalmente, com propriedades mecânicas adequadas para a aplicação pretendida (força de rotura máxima de 35.9 MPa). Por fim, validou-se o desenvolvimento de compósitos usando um sistema redox ecológico para a polimerização do AESO, bem como o acabamento com um biocida e o tingimento dos compósitos. A associação de óleos vegetais ativados com membranas de CB constituiu uma abordagem inovadora e promissora para o desenvolvimento de um produto amigo do ambiente, quase exclusivamente composto de materiais biológicos e recicláveis, com potencial para aplicação nas indústrias do têxtil e do calçado, contribuindo para a redução da dependência do couro animal. Palavras-chave: celulose bacteriana; óleos vegetais ativados; biocompósitos; alternativa ao couro; sustentabilidade.
vi Abstract Development of bacterial cellulose composites as an alternative to leather Leather is a natural material widely used in the textile and footwear industries. However, its production process together with the animal growth process has a high environmental and human impact. With consumers increasingly aware of environmental and animal welfare issues, there is a growing demand for sustainable and cruelty-free alternatives to leather. This work aimed the development of composites comprising bacterial cellulose (BC), as structural material, and activated vegetable oils and other hydrophobic polymers, as flexibilizing and hydrophobizing agents, as an alternative product to leather. For this, it was tested a novel approach for the modification of BC, combining simplicity, potential for large-scale application and low cost, based on the use of a simple process of exhaustion for the incorporation of the polymers into the BC matrix. All the combinations resulted in hydrophobic composites (maximum contact angle of 138°). Firstly, two commercial hydrophobic polymers from the textile industry were used, a softener based on polydimethylsiloxane (PDMS) and a hydrophobizer based on perfluorocarbon (PFC). The obtained composites were breathable (maximum water vapor permeability of 373 g·m−2·24 h−1) and with satisfactory performance regarding mechanical properties (maximum tensile strength of 48.4 MPa). To increase the bio-based content in the composite, the acrylated epoxidized soybean oil (AESO) was tested in a mixture with the PDMS-based polymer and polyethylene glycol (PEG) 400. The BC composites owned distinct performances, manipulated by varying the percentage of polymer. Then, composites were developed with the AESO resin previously emulsified and in mixtures with PDMS, PFC and PEG, resulting in composites thermally stable (up to 200 °C) and, overall, with suitable mechanical properties for the proposed application (maximum tensile strength of 35.9 MPa). Finally, it was validated the development of composites using an ecological redox system for the polymerization of AESO, as well as the finishing with a biocide and the dyeing of the composites. The association of activated vegetable oils with BC membranes constituted an innovative and promising approach for the development of an environmentally friendly product, almost exclusively composed of biological and recyclable materials, with potential for application in the textile and footwear industries, contributing to the reduction of the animal hide dependency. Keywords: bacterial cellulose; activated vegetable oils; biocomposites; leather alternative; sustainability.
vii Table of content DIREITOS DE AUTOR E CONDIÇÕES DE UTILIZAÇÃO DO TRABALHO POR TERCEIROS ...... ii ACKNOWLEDGEMENTS ................................................................................................... iii STATEMENT OF INTEGRITY .............................................................................................. iv Resumo ............................................................................................................................. v Abstract ............................................................................................................................ vi Acronyms and abbreviations ............................................................................................. xi Figure index ................................................................................................................... xiii Table index ...................................................................................................................... xv Chapter 1 ......................................................................................................................... 1 Introduction...................................................................................................................... 1 1.1. Preamble ............................................................................................................................................ 1 1.2. Structure of the thesis ..................................................................................................................... 4 Chapter 2 ......................................................................................................................... 6 Literature overview .......................................................................................................... 6 2.1. The leather industry and its environmental impact ..................................................................... 6 2.2. Synthetic alternatives to leather ..................................................................................................... 9 2.3. Eco-friendly alternatives to leather .............................................................................................. 11 2.3.1. Alternatives to leather obtained from sustainable natural resources ................................ 11 2.3.2. Alternatives to leather obtained by biofabrication ............................................................... 14 2.4. Bacterial cellulose .......................................................................................................................... 17 2.4.1. Bacterial cellulose production and properties ...................................................................... 17 2.4.2. General applications of bacterial cellulose ........................................................................... 20 2.4.3. BC in the textile and shoe industry ......................................................................................... 22 2.4.3.1. BC for the fashion industry ............................................................................................................. 22 2.4.3.2. BC coated on fibers, yarns, fabrics ................................................................................................. 25 2.4.3.3. Development of BC macrofibers ..................................................................................................... 27 2.4.3.4. Improvement of BC flexibility, hydrophobicity, and mechanical properties ....................................... 28 2.4.3.5. BC purification, bleaching, and dyeing ............................................................................................ 30 2.5. Vegetable oils .................................................................................................................................. 32 Chapter 3 ....................................................................................................................... 35 Development of BC/PDMS/PFC composites ................................................................... 35 3.1. Abstract ............................................................................................................................................ 35 3.2. Introduction ..................................................................................................................................... 36 3.3. Materials and methods .................................................................................................................. 37 3.3.1. Materials .................................................................................................................................... 37
xiv Figure 26. Photos of the dyed BC composites. Letters (a–i) correspond to the experimental conditions described in Section 6.3.3.2. Simultaneous dyeing and production of the BC-based composites (a–f) and dyeing of dry composites (g–i). ............................................................................................................................................. 99
xv Table index Table 1. Properties of leather ........................................................................................................................... 7 Table 2. Advantages and disadvantages of synthetic leathers. ........................................................................ 10 Table 3. Advantages and disadvantages of natural, synthetic, and vegetable leather. ...................................... 11 Table 4. Examples of commercial alternatives to leather obtained from sustainable natural resources. ............ 14 Table 5. Examples of alternatives to leather obtained by biofabrication. .......................................................... 16 Table 6. Properties of bacterial cellulose ........................................................................................................ 19 Table 7. Examples of BC potential applications. ............................................................................................. 21 Table 8. Summary table on the exploitation of BC for the fashion industry. ..................................................... 24 Table 9. Coating of fibers, yarns, and fabrics with BC nanofibers. ................................................................... 26 Table 10. BC macrofibers. ............................................................................................................................ 28 Table 11. Improvement of BC properties for textile applications. .................................................................... 29 Table 12. BC purification, bleaching, and dyeing. ........................................................................................... 31 Table 13. Characteristics of the finishing polymers used.a .............................................................................. 37 Table 14. Mass per unit area and percentage of polymers in brackets. ........................................................... 42 Table 15. Average contact angle values (°) measured for drops of water, PEG 200 and glycerol. .................... 46 Table 16. Thickness, Young’s modulus, tensile strength, and elongation at break. .......................................... 51 Table 17. Formulations used in the production of BC composites. ................................................................. 55 Table 18. Thickness, mass per unit area and polymers content of BC composites. ......................................... 57 Table 19. Combinations of surfactants used to study the effect of HLB on the AESO emulsion stability. .......... 70 Table 20. Proportions of the polymers in the aqueous mixture used in the production of BC composites. ........ 71 Table 21. Thickness, mass per unit area and polymer content of the composites. .......................................... 78 Table 22. Thermal degradation data obtained from DSC, TGA and DTG curves of dried BC and BC composites. ....................................................................................................................................................................... 84 Table 23. Tensile strength and elongation at break of dried BC and BC composites. ....................................... 86 Table 24. Proportions of each component in the mixtures used in the production of BC composites. .............. 91 Table 25. Conditions used in the antimicrobial finishing of BC composites. .................................................... 92 Table 26. Properties of the BC and BC composites. ....................................................................................... 95
xvi To Professor Pedro Souto “Prometo-te que estarei em tudo aquilo que te ensinei e que aprenderás por ti.”
1 Chapter 1 Introduction 1.1. Preamble In recent years, one of the problems the world has been facing concerns climate change, caused primarily by greenhouse gas emissions. In 2015, the United Nations announced 17 Sustainable Development Goals, challenging organizations to work in ways that improve human life and planet quality. Two of these goals rely on the availability and sustainable management of water and sanitation for all and ensure sustainable consumption and production patterns. These goals can be achieved namely by reducing pollution and minimizing the release of hazardous chemicals and materials, and through efficient management of the planet’s natural resources (United Nations, 2015). The leather industry sector presents a production chain of high economic and social value. Worldwide, per year, more than 20 billion square feet of leather and 4.5 billion pairs of upper leather shoes are produced. The market value of hides, skins, leather, and leather footwear is more than 82 billion USD (FAO, 2015). However, leather processing has a high environmental and human impact, with large amounts of chemicals and water being used. In the whole process, for each ton of raw skin, about 500 kg of chemicals are added (Black et al. , 2013), and 30,000 to 50,000 L of water are consumed (Sathish et al. , 2016). Worldwide, the leather industry generates per year 548 billion L of wastewater (Sathish et al. , 2016) and 600,000 tons of solid waste classified as dangerous (Bizzi et al. , 2020). In addition, the livestock sector, from which animals’ skins are obtained to produce leather, consumes a large amount of natural resources, contributing to 14.5% of the global greenhouse gas emissions. The majority of these emissions comes from the feed production stage, followed by deforestation due to the expansion of pasturelands and croplands for livestock production (Rojas-Downing et al. , 2017). For decades, the development of leather analogues has been pursued by the scientific community and leather industry. This effort led to the appearance of various materials, some synthetic, other naturals.
Chapter 1 – Introduction 2 Despite the increasing interest and market pull, the market penetration of these alternative products has been relatively modest. This research intends to develop an ecological alternative to leather by the production of composites from bacterial cellulose (BC) and different polymers, in particular activated vegetable oils, contributing to the reduction of the animal hide dependency, and thus, to a more environmentally sustainable approach towards making available, to a wide and important market, a natural-based raw material for leather applications. BC is a biopolymer produced by bacteria fermentation in the form of a gelatinous film that consists of a porous 3D structure of pure cellulose nanofibers with excellent mechanical properties and high specific surface area (Wu et al. , 2016). Nevertheless, the hydrophilic nature of BC and the loss of flexibility and porosity upon drying due to the collapse of the 3D network has limited its application in the textile and footwear industry. Surface functionalization strategies have been usually used to modify the surface properties of cellulosic materials, to improve its compatibility with hydrophobic matrices, often being detrimental to the mechanical and physico-chemical properties of BC (Hu et al. , 2011; K.-Y. Lee et al. , 2011; Frone et al. , 2018). The alternative and new strategy here proposed uses BC as structuring material, capable of housing emulsified hydrophobic polymers as flexibilizing and hydrophobizing agents, as a simple approach to overcome these constraints (Figure 1). In this approach, impregnation of the BC was archived by an exhaustion process, a method widely used in textile dyeing. The work here done was framed within the Portuguese project BUILD – Bacterial Cellulose Leather, supported by the program COMPETE 2020. This project involved the Centre of Biological Engineering (CEB/UM) and the Centre for Textile Science and Technology (2C2T/UM) from University of Minho, Satisfibre, S.A., a spinoff from CEB/UM, KYAIA - Fortunato O. Frederico & Cª Lda, a major Portuguese shoe manufacturer company and the Technological Center for Footwear in Portugal (CTCP).
Chapter 1 – Introduction 3 Figure 1. Schematic representation of the strategies here taken towards the preparation of BC composites.
Chapter 1 – Introduction 4 1.2. Structure of the thesis This thesis is organized in the following chapters (Figure 1): Chapter 1. Introduction This chapter presents the purpose of the research and the thesis outline. Chapter 2. Literature overview This chapter includes a comprehensive overview of the leather industry and its impact on the environment, the existing synthetic alternatives to leather, and the efforts made more recently in the development of ecological alternatives. Additionally, the bacterial cellulose properties and applications are reported, and its potential for the textile and footwear industries, including the scientific studies, are reviewed. Finally, efforts towards the development of composites based on modified soybean oil are also summarized. Chapter 3. Development of BC/PDMS/PFC composites In this chapter, a novel approach is tested for the bulk and surface modification of bacterial cellulose. Malleable, breathable, and water impermeable BC-based nanocomposites were developed by impregnating BC membranes with two commercial hydrophobic polymers used in textile finishing, Persoftal MS (polydimethylsiloxane (PDMS)) and Baygard EFN (perfluorocarbon (PFC)), by an exhaustion process. The properties of the obtained bio-based composites were characterized. The work here done resulted in the following publication: Fernandes, M., Gama, M., Dourado, F. and Souto, A. P. (2019) “Development of novel bacterial cellulose composites for the textile and shoe industry,” Microbial Biotechnology , 12(4), pp. 650–661. Chapter 4. Development of BC/PDMS/PEG/AESO composites In chapter 4, in order to yield a high bio-based content composite with hydrophobic character, the acrylated epoxidized soybean oil (AESO) resin was incorporated into the bulk of BC membranes, in a mixture containing also the PDMS-based polymer and polyethyleneglycol (PEG) 400, as a plasticizer, allowing to obtain a product with greater elasticity, as well as, contributing to improve the interfacial adhesion between the BC and the other polymers. The properties of the obtained bio-based composites were characterized. The work here done resulted in the following publication:
Chapter 1 – Introduction 5 Silva. F. A. G. S., Fernandes, M., Souto, A. P., Ferreira, C., Dourado, F. and Gama, M. (2019) “Optimization of bacterial nanocellulose fermentation using recycled paper sludge and development of novel composites,” Applied Microbiology and Biotechnology , 103(22), pp. 9143–9154. Chapter 5. Development of BC/emulsified AESO composites In this chapter, bio-based composites comprising bacterial cellulose and acrylated epoxidized soybean oil previously emulsified were developed. In the first part, the optimum conditions for the emulsification of AESO were studied. The required hydrophilic–lipophilic balance (HLB) and the AESO emulsion stability were evaluated. Then, a stable AESO emulsion was used to develop BC-based composites. PEG, PDMSand PFC-based polymers were also added to the emulsion, with the mixtures being diffused into the BC 3D nanofibrillar matrix by an exhaustion process. The properties of the obtained bio-based composites were characterized. The work here done resulted in the following publication: Fernandes, M., Souto, A. P., Gama, M. and Dourado, F. (2019) “Bacterial cellulose and emulsified AESO biocomposites as an ecological alternative to leather,” Nanomaterials , 9(12), pp. 1710–1727. Chapter 6. Development of BC-based composites polymerized with H2O2/AA, finishing and dyeing In this chapter, the polymerization of the AESO emulsion using an ecological redox system, peroxide hydrogen and L-ascorbic acid, before exhaustion process, were tested. Also, the finishing with a biocide and the dyeing of the BC-based composites were tested. The properties of the obtained bio-based composites were characterized. The work here done resulted in the following publication: Fernandes, M., Souto, A. P., Dourado, F. and Gama, M. (2021) “Application of bacterial cellulose in the textile and shoe industry: Development of biocomposites,” Polysaccharides , 2(3), pp. 566–581. Chapter 7. Conclusions and suggestions for future work This chapter presents the major conclusions of the thesis and future perspectives for this research work.
6 Chapter 2 Literature overview 2.1. The leather industry and its environmental impact The world production of leather is approximately 20 billion square feet per year and are produced about 4.5 billion pairs of leather shoes (FAO, 2015). With a 50% share in the EU, footwear, in general, remains the dominant sector for finished leather. Also in the EU, the garment industry occupies approximately 20%, furniture and car upholstery represent 17%, and the leather goods sector 13% (Black et al. , 2013). As a high-value noble material, leather has a unique structure that offers advantageous properties such as mechanical strength, flexibility, and breathability. The leather-making operation involves a sequence of complex chemical and mechanical processes, necessary to transform the animals' skins, a byproduct of meat industry, into a functional material. The different processing steps can be divided into the main sets of operations: beamhouse, tanning, post-tanning, and finishing. In the first phase, different processes are carried out to restore moisture, remove tissue and fat, and give flexibility. The tanning process consists of stabilizing the collagen fibers. In the post-tanning operations, touch properties, softness, and uniformity are improved by filling the weaker areas, and in the final step, leather is finished to enhance its appearance (Black et al. , 2013; Laurenti et al. , 2016). Tanning is the most important operation which provides permanent stability to the material. It can be done with vegetable or mineral tanning agents, but chromium agent is the most used because it offers superior softness, high thermal and water stability and it is less time-consuming (Dixit et al. , 2015). Structurally, leather is characterized by a three-dimensional network of bundles of collagen fibers (about 80 µm in diameter), composed of fibers (1–4 µm), which in turn are composed of microfibrils (0.08– 0.10 mm). Each microfibril consists of several protofibrils (about 1.5 nm), formed by bundles of polypeptide chains (Hiokki, 2014). Collagen fibrils have inherent strength and their arrangement is crucial in physical properties, such as strength, smoothness, and aesthetic properties. The hierarchical structure
Chapter 2 – Literature overview 7 is complex with different layers, the grain on the outer surface, and the corium beneath. The corium presents more collagen, highly oriented and compacted, which offers most of the strength to leather (Basil-Jones et al. , 2010). The capillaries among collagen fibers together with the hydrophilic groups on the collagen chains make leather permeable to water vapor (Ugbaja et al. , 2016). Table 1 presents some properties of leather. Regarding the alternative products mentioned in the next sections, no data on their properties was found. Table 1. Properties of leather Property References Fiber diameter about 80 µm (Hiokki, 2014) Static water absorption 147.5–240 mL·100g−1·24 h−1 249.57 / 307.19 mL·100 g−1 (chrome, vegetable) (Kılıç et al. , 2017) (Zengin et al. , 2016) Dynamic water absorption 103.31–136.31% (24 h) 52.06 / 99.61% (chrome, vegetable) (Nasr, 2017) (Zengin et al. , 2016) Water vapor permeability 2.6 mg·cm−2·h−1 1.41–5.43 mg·cm−2·h−1 18.71–114.34 / 330.54–337.82 mg·cm−2·h−1 (finished, unfinished) 23.7–42 g·m−2·h−1 (coated, uncoated) (Tamilselvi et al. , 2019) (Nasr, 2017) (Ugbaja et al. , 2016) (Gulbiniene, Jankauskaite and Arcilauskaite, 2003) Water vapor sorption 33–79 g·m−2 (Gulbiniene, Jankauskaite and Arcilauskaite, 2003) Tensile strength 33.0–34.3 N·mm−2 13.07–22.53 N·mm−1 276.02–329.29 kg·cm−2 18–26 N·mm−2 6.6–10.9 N·mm−2 (Tamilselvi et al. , 2019) (Kılıç et al. , 2017) (Nasr, 2017) (Sureshkumar et al. , 2012) (Sudha et al. , 2009) Elongation 38.8–41.2% 56.07–84.63% 48.19–68.36% 38–42% 58% (Tamilselvi et al. , 2019) (Kılıç et al. , 2017) (Nasr, 2017) (Sureshkumar et al. , 2012) (Sudha et al. , 2009) Tear strength 50.3–52.7 N·mm−1 80.55–114.4 N·mm−1 69.23–86.94 kg·cm−1 56–60 N·mm−1 (Tamilselvi et al. , 2019) (Kılıç et al. , 2017) (Nasr, 2017) (Sureshkumar et al. , 2012) Stitch tear strength (double hole) 167.09–208.58 N·mm−1 37.9–52.9 N·mm−1 (Kılıç et al. , 2017) (Sudha et al. , 2009) Despite its global use through mankind history and its economic value, the leather industry is considered one of the most polluting industries (Yorgancioglu, Başaran and Sancakli, 2020). Consequently, leather production is accompanied by several challenges associated to the high environmental impact and increasing consumer demand for eco-friendly products, as well as increasing regulatory constrains towards the reduction of the environmental impact. Nowadays, consumers are becoming more aware of
Chapter 2 – Literature overview 14 2019). Designer Uyen Tran has developed a leather alternative called Tômtex that is made from seafood shells and coffee grounds. After collecting seafood waste, chitin is extracted and mixed with coffee waste, and the mixture is placed in a mold and left to dry for two days (Hahn, 2020). The Italian company Frumat developed a vegan leather-like material called Apple Ten Lork that is made from apple cores and skins, a biological industrial waste product (Materials District, 2019). Fruitleather Rotterdam has also developed an eco-friendly process that converts leftover mangoes into a durable leather-like material that involves mashing, cooking, and drying (Fruitleather, 2020). Table 4. Examples of commercial alternatives to leather obtained from sustainable natural resources. Leather alternatives Raw material Producer / Creator Cork skin Cork Pelcor Nuo (formerly Ligneah) Wood Nuo Design (MyMantra) Piñatex Pineapple plant leaves Ananas Anam Palmetti Areca palm leaves Tjeerd Veenhoven MuSkin Mushrooms ( Phellinus ellipsoideus ) GradoZero Espace Desserto Nopal cactus Adrián López Velarde and Marte Cázarez Lino leather Linoleum (plant-based oils/resins), jute Don Yaw Kwaning Vegea Grape marc VEGEA srl Coffee leather Coffee grounds waste Alice Genberg Tômtex Seafood shells and coffee grounds waste Uyen Tran Apple Ten Lork Apples waste Frumat Fruitleather Discarded fruit Fruitleather Rotterdam 2.3.2. Alternatives to leather obtained by biofabrication With the increasing search for more sustainable leather alternatives, some progress has been done focused on biofabrication processes. The metabolic processes of living organisms such yeast, fungi, and
Chapter 2 – Literature overview 15 bacteria produce yeast-derived collagen, fungal biomass, and bacterial cellulosic materials, respectively, which are being explored for the development of leather substitutes (Table 5). Modern Meadow is a Brooklyn startup founded in 2011 that is developing a process for making leather without using animal skins. The process involves culturing collagen protein from animal cells, which is then structured in a material that replicates natural leather. For the transformation of raw synthetic leather into leather, collagen sheets are subjected to a simplified tanning process, which requires 80% less of the chemicals used in traditional tanning. Unlike traditional leather, with this technology, the shape and size can be adjusted, eliminating the waste resulting from the imperfections that exist in traditional leather and, in the future, it may be possible to improve the product’s properties such as strength or flexibility. In 2017 they launched their first branded biofabricated leather material called Zoa™ (Leber, 2016; Hao, 2017; Modern Meadow, 2020). The startup MycoWorks (San Francisco) was founded in 2013, and in 2015 they started producing a sustainable and versatile leather-like material made with mushrooms (mycelium). They called it Reishi™ and is described as soft, malleable, and waterproof material that in the future may replace leather and foams in shoes. This type of leather is made from pure mycelium, the key ingredient, in the form of microscopic threads formed at the base of the mushrooms. The company mainly uses Ganoderma lucidum , also known as the Reishi mushroom. In the production of this material, fungi are collected from nature, and pieces of mycelium are placed in bottles with discarded organic material (agricultural waste). After a few days, the fibers of the mycelium expand, forming a 3D structure of microscopic threads. The mycelium can be cultivated and manipulated in a multitude of textures and shapes, by changing the growth environment, developing differently according to the available nutrients, temperature, light, humidity, and gas in the environment. It is also possible to add other materials, such as oils, to obtain a product with different characteristics, more resistant or flexible, heavy or light. Despite the advantage that a piece the size of a bovine skin can be produced in a few weeks, the process takes place in a closed circuit (without waste) and with a variety of shapes and textures achievable. However, the material has not yet been tested for a series of important characteristics, such as biological decomposition or durability/use behavior (Peters, 2016; Robinson, 2016; Tu, 2016). The company Bolt Threads also started to produce a vegan alternative leather made from mushroom roots called Mylo™. The process consists of growing the mycelium cells on beds of renewable organic matter with controlled temperature and humidity, in order to make the mycelium grow upward and assemble into an organized interconnected 3D network. The mycelium mat is then harvested and processed, tanned and dyed, and
Chapter 2 – Literature overview 16 imprinted with the desired pattern. The resulted material has a leather-like look and is durable and abrasion-resistant (Bolt Threads, 2020). Other alternatives to leather produced by biofabrication for application in the textile and footwear industries are that consisting of bacterial cellulose. Some of these examples are presented in Table 5 and are described later in section 2.4.3. Table 5. Examples of alternatives to leather obtained by biofabrication. Biofabricated leather Materials used Creator Zoa™ Collagen Modern Meadow Reishi™ Mycelium (Reishi mushrooms) MycoWorks Mylo™ Mycelium Bolt Threads BioCouture project Bacterial cellulose (kombucha-green tea) Suzanne Lee ScobyTec BNC Bacterial cellulose (kombucha-black tea) SCT Materials Corporation Soya C(o)u(l)ture project Bacterial cellulose (soya waste) XXLab Malai Bacterial cellulose (coconut water) Malai Design & Materials
Chapter 2 – Literature overview 17 2.4. Bacterial cellulose Cellulose is an almost inexhaustible and sustainable natural polymeric raw material and, being an alternative to products derived from the petrochemical industry, it is considered as one of the most promising renewable resources for the growing investment in ecological and biocompatible products with a performance at the same or better level than conventional non-renewable materials (Klemm et al. , 2005; Wan et al. , 2009; Hu et al. , 2014; Tang et al. , 2015). It can be obtained from plants, some species of bacteria, algae, fungi, and tunicates (Klemm et al. , 2005; Mishra, Sabu and Tiwari, 2018). Bacterial cellulose (BC) is a biopolymer produced by fermentation by bacteria such as the genus Komagataeibacter . Under static culture conditions, BC is produced as a gelatinous film that consists of a 3D structure of pure cellulose nanofibers. Despite having a chemical composition identical to that of vegetable cellulose, BC differs in terms of structure and mechanical properties, presenting several distinct advantages (Lee, Blaker and Bismarck, 2009; Wan et al. , 2009; Retegi et al. , 2012; Wu et al. , 2016). 2.4.1. Bacterial cellulose production and properties BC is synthesized in a multi-step process involving individual enzymes, catalytic complexes, and regulatory proteins (Lee et al. , 2014). Figure 2 illustrates the bacterial cellulose biosynthesis process (Portela et al. , 2019; Zhong, 2020). In the first stage, the glucose in the medium is transported into the bacteria and the polymerization of the glucose molecules occurs between the outer membrane and the cell's cytoplasm, forming 1,4-β – glucosidic chains. Then, these chains are secreted through cellulose synthase complex (each cell has 50 to 80 pores along its axis) and 10-15 chains form a 1.5 nm wide protofibril. The organization and crystallization of the protofibrils through hydrogen bonds give rise to microfibrils with 2 to 4 nm in diameter and, finally, the microfibrils are grouped on an bundle with 20 to 100 nm in diameter, thus forming a cellulose film with a three-dimensional structure that composes BC (Iguchi, Yamanaka and Budhiono, 2000; Castro et al. , 2011; K.-Y. Lee et al. , 2014; Rajwade, Paknikar and Kumbhar, 2015).
Chapter 2 – Literature overview 18 Figure 2. Schematic illustration of the biosynthesis of cellulose molecules and their assembly into nanofibers. Under static culture, BC production takes place in the form of uniformly spaced layers parallel to the air/liquid interface. At the beginning of biosynthesis, the inoculum bacteria increase their population through the consumption of oxygen dissolved in the medium and, since they are aerobic, they accumulate at the air/liquid interface of the culture medium. During this time, they synthesize a certain amount of cellulose into the liquid phase, descending as the biosynthesis progresses. The new cells diffuse through the cellulose matrix synthesized to the air/liquid interface to start producing a new layer, and so on, until
Chapter 2 – Literature overview 19 the nutrients in the medium are exhausted (Budhiono et al. , 1999; Klemm et al. , 2011; Ruan et al. , 2016). Table 6 summarizes the properties of bacterial cellulose. (Lee, Blaker and Bismarck, 2009) Table 6. Properties of bacterial cellulose Properties References Degree of polymerization up to 8000 (Wu et al. , 2016) Crystallinity 60–90%. (Klemm et al. , 2005) Nanofibers’ diameter 20–100 nm (Wu et al. , 2016) Nanofibers’ length 1–9 µm (Foresti, Vázquez and Boury, 2017) Density 1.50 g·cm−3 1.25 g·cm−3 (Hervy et al. , 2018) (Lee, Blaker and Bismarck, 2009) Surface area 2.7–37 m2·g−1 (Kim, Nishiyama and Kuga, 2002) Water absorption 610.5% 320% (Potivara and Phisalaphong, 2019) (Rathinamoorthy et al. , 2019) Water vapor permeability 765.95–1045.55 g·m−2·24 h−1 2.38×10−11 g·m−1·s−1·Pa−1 151 g·m−2·24 h−1 1.26×10−10 g·m−1 h−1·Pa−1 1–11×10−13 g·m−1·s−1·Pa−1 (Kamal, Misnon and Fadil, 2020) (Cazón, Velázquez and Vázquez, 2019) (Rathinamoorthy et al. , 2019) (Jebel and Almasi, 2016) (Tomé et al. , 2010) Young’s modulus 1044 MPa 5–17 GPa 93.8 MPa 138 GPa 114 GPa 15–35 GPa (Cazón, Velázquez and Vázquez, 2019) (Potivara and Phisalaphong, 2019) (Jebel and Almasi, 2016) (Hu et al. , 2011) (Lee, Blaker and Bismarck, 2009) (Klemm et al. , 2005) Tensile strength 20.8 MPa 70–300 MPa 26.3 MPa 2 GPa 200–300 MPa (Cazón, Velázquez and Vázquez, 2019) (Potivara and Phisalaphong, 2019) (Jebel and Almasi, 2016) (Hu et al. , 2011) (Klemm et al. , 2005) Elongation 2.3% 0.5%–5.0% 6.1% 1.5–2.0% (Cazón, Velázquez and Vázquez, 2019) (Potivara and Phisalaphong, 2019) (Jebel and Almasi, 2016) (Klemm et al. , 2005) The properties of cellulose produced by bacteria can be controlled by changing the conditions of the fermentation, such as the type of strain, the composition of the culture medium, and environmental factors, namely pH, temperature, dissolved oxygen content, and type of culture (static or with agitation) (K.-Y. Lee et al. , 2014; Douglass et al. , 2018). Its uniqueness is due, in the first place, to the fact that it is free of lignin, hemicellulose, and pectin, which are present in the cellulose of plants, and therefore there is no need for extra processing to remove them (Lee, Blaker and Bismarck, 2009; Wu et al. , 2016). At the microstructure level, BC presents a porous interconnected structure. The particular mechanical properties result from its randomly organized three-dimensional network of interconnected nanofibers,
Chapter 2 – Literature overview 20 with a diameter of 20-100 nm and a few micrometers in length, resulting in a high specific surface area (Tang et al. , 2015; Wu et al. , 2016), properties which are very advantageous for the production of composite materials (Lee, Blaker and Bismarck, 2009). These nanofibers can be oriented uniaxially by the application of tension during drying (K.-Y. Lee et al. , 2014). Regarding physical properties, BC exhibits high crystallinity, which, coupled with its’ 3D nanofibrillar architecture, results in a high Young’s modulus. It also has a high degree of polymerization, high water holding capacity, and high moldability in situ (during fermentation) and ex situ (after fermentation) (Lee, Blaker and Bismarck, 2009; Wu et al. , 2016). 2.4.2. General applications of bacterial cellulose The unique properties of BC compared to vegetable cellulose have supported the development of several applications in different areas, such as food, paper, biomedical, aerogel, electronic devices, and textile and footwear industries (Table 7). Despite this wide range of possible applications of BC, only a few products reached commercialization, particularly in the food, biomedical and cosmetic areas (Jang et al. , 2017). BC's main commercialization exists in the form of nata de coco , a gelatinous product resulting from the fermentation of coconut water that is preserved in syrup and often served with fruit, drinks, creams, or ice cream. Pure cellulose can also be safely processed in various foods, acting as a thickener, stabilizer, gelling agent, or low-calorie substitute (Dourado et al. , 2016; Jang et al. , 2017; Gama and Dourado, 2018). In relation to electronic products, high-fidelity loudspeakers, and headphones with acoustic diaphragms from BC are marketed by Sony Corporation (Iguchi, Yamanaka and Budhiono, 2000). However, the biomedical area is the one that has received more attention, with several medical products already commercialized, with the treatment of burns and skin wounds being the main application of BC membranes (Ludwicka et al. , 2016) . In terms of cosmetics, BC facial masks are widely known in Asian markets (Jang et al. , 2017).
Chapter 2 – Literature overview 21 Table 7. Examples of BC potential applications. Sector Applications Food Food: nata de coco , artificial meat (Dourado et al. , 2016) Additive: thickener, stabilizer, gelling agent, emulsifier, bonding agent (Jozala et al. , 2016) Food packaging: sausage casings (Padrão et al. , 2016) (Dourado et al. , 2016) Paper Packaging (Pradipasena, Chollakup and Tantratian, 2018) Paper restoration (Santos et al. , 2016) Ultra-filtration membranes (Mautner et al. , 2015) (Santos et al. , 2016) Biomedical Wound care (Czaja et al. , 2007) Tissue engineering: blood vessels (Scherner et al. , 2014), meniscus implant (Bodin et al. , 2007), urethral reconstruction (Huang et al. , 2015) Drug delivery (Abeer, Mohd and Martin, 2014) (Czaja et al. , 2007) (Scherner et al. , 2014) (Bodin et al. , 2007) Aerogels Filtration/separation Thermal and acoustic insulation (Sai et al. , 2014, 2015) (Sai et al. , 2015) Electronic devices OLEDs (Nogi and Yano, 2008; Pinto et al. , 2015) Acoustic Membranes (Iguchi, Yamanaka and Budhiono, 2000) Solar cells (Pleumphon et al. , 2017) (Nogi and Yano, 2008) (Pinto et al. , 2015) Textile and footwear Clothing (Lee, 2011; Chan, Shin and Jiang, 2018) Footwear (Costa, Rocha and Sarubbo, 2017; Rotor, 2017) (Chan, Shin and Jiang, 2018) (Costa, Rocha and Sarubbo, 2017)
Chapter 2 – Literature overview 22 2.4.3. BC in the textile and shoe industry Regarding the application of BC in the clothing and footwear sectors, the first proof of concept of the use of BC as an alternative to leather was made in the 1990s, in the Philippines, where handmade BC was pressed and tanned to produce a material with similar properties to leather (Rotor, 2017). In this last decade, the well-known fashion designer Suzanne Lee, in England, expanded the possibility of using BC in the manufacture of clothing and footwear in an artistic and ecological project called BioCouture. BC was produced handmade, from fermentation with a consortium of microorganisms (kombucha) in a nutrient medium enriched with sugar; then cellulose sheets were washed, adjusted to a pre-defined shape, depending on the final piece to be obtained, dried, and dyed (Lee, 2011). The German start-up ScobyTec developed a vegan alternative to leather made of bacterial cellulose produced from kombucha, which they used to make various products, like gloves, children’s shoes, and business handbags. The material called ScobyTec BNC possesses high mechanical strength and is non-flammable (Material District, 2019). In the project SOYA C(O)U(L)TURE, settled by the Indonesian collective XXlab, bacterial cellulose was produced from the liquid waste in tofu production. The cellulose sheets were further pressed, dried, colored, and coated (Sick-Leitner, 2015). The company Malai Design & Materials from India is also using by-products to produce bacterial cellulose but in this case coconut water. The obtained BC sheets are processed and can be modified by incorporating natural fibers, resins, and gum to create a leather-like material (Raut, 2019). Several academic studies have been conducted with the intention of developing bacterial cellulose-based materials for the textile and fashion industry (Table 8, Table 9, Table 10, Table 11 and Table 12). 2.4.3.1. BC for the fashion industry The receptivity of BC films produced from kombucha culture with different incubation times, carbon sources, and medium concentrations by professional designers was studied through a qualitative assessment, in terms of comfort and appearance, and it was concluded that BC is useful for fashion applications (Ng and Wang, 2015, 2016). The acceptance of BC in apparel or other related products by the consumers was also explored through an online survey based on visual images of a vest prototype (Lee, 2016; Lee, Li and Nam, 2016). In another work, the acceptance of BC, produced from the kombucha fermented medium, as a novel material for fashion was evaluated subjectively. The participants accepted BC for fashion accessories, but not as a clothing material, based on its thinness, translucency,
Chapter 2 – Literature overview 23 unpleasant odor, and skin-like and worn appearance. However, material texture and novelty were found to be favorable characteristics (Ghalachyan, 2018). The moldability of BC and the possibility of growing it in any shape are advantageous for the development of fashion products. Materials in the form of 2D sheets, singular 3D, and multiple 3D to be used in fashion creation were produced by exploring BC growth (Ng and Wang, 2016). BC-based 3D art integrating SMDLED through conductive threads was developed by molding BC using a preform (Ng, 2017). The peculiarity of BC to be produced in the desired shape was used to produce clothing with zero-waste. Each part of the garment was fermented to the required size and shape, then dyed and finished with animal oil or wax (Chan, Shin and Jiang, 2018). The moldability of BC was also studied by placing wet BC, produced along with a natural dye extract, in a preform, followed by drying (Tyurin et al. , 2019). The attention given to BC to be used alternatively to leather and cotton-based products is due to its leatherlike appearance and cellulose content. The influence of nitrogen and carbon sources on the production of BC was studied and the properties compared with natural leather. The BC nonwoven obtained presented a leather-like appearance and its tensile strength was two times higher, but half the elongation, when compared with bovine top-grain leather (Yim, Song and Kim, 2017). BC properties were also compared with cotton fabric in order to analyze its potentiality in the apparel and textile industry. The authors concluded that BC presents good folding endurance and the tensile strength is acceptable for clothing purposes, but properties related to moisture management should be improved (Rathinamoorthy et al. , 2019). The effect of drying temperature on BC properties was studied by analyzing BC obtained through kombucha tea fermentation and dried at different temperatures. It was concluded that BC material is sensitive to drying temperature, it becomes stiffer and loses strength when dried at higher temperatures. And, although the water vapor permeability is compared to coated fabric and leather, further improvement is needed for its application in the fashion industry (Domskiene, Sederaviciute and Simonaityte, 2019).
Chapter 2 – Literature overview 30 Flexible BC Production of BC from kombucha, in static conditions for 2 weeks. Freeze-dried BC samples were added to a glycerol aqueous solution and autoclaved at 121 °C for 15 min. Then rinsing with distilled water and freeze-dried. Stearic acid ethanol solution was spread using a brush and streamed with hot air (70–75 °C). BC with increased strength, elasticity, and inflammable properties. (Kamiński et al. , 2020) 2.4.3.5. BC purification, bleaching, and dyeing The possibility of giving certain colors to the materials is a fundamental feature in the textile and footwear sectors. Several studies have been conducted for the color modification of BC, including bleaching, dyeing with natural and artificial dyes, and in situ and ex situ dyeing processes (Table 12). After cultivation, BC presents a natural yellowish-brown color derived from the culture medium. Washing of BC with 3% NaOH solution results in the effective removal of bacteria and the remnants of the culture medium that does not affect the BC nanoscale 3D network structure. In order to ensure the subsequent uniform dyeing and bright colors, bleaching with 5% H2O2 solution for 60 min at 90 °C removed the brown-yellow color of BC (white index of 73.15), without deforming the cellulose structure (Han, Shim and Kim, 2019). Recently, the effect of sodium hydroxide concentration on morphology, physical and chemical structure, and water vapor permeability (WVP) of BC membranes was studied. It was shown that by removing impurities, such as organic compounds, nucleic acids, and proteins generated by during the fermentation process, BC membrane breathability can be improved (Kamal, Misnon and Fadil, 2020). Dyeing of BC was carried out by producing BC in the presence of a direct acid or basic dye in the culture media. Optical microscopy observation showed that the direct and basic dyestuffs stained the BC, but the acid one did not. Analysis of wide angle X-ray diffraction (WAXD) data indicated that direct dyestuffs inhibited the crystallization of BC above 0.05 wt% dyestuff concentration in the culture medium, but basic dyestuff had almost no influence on the BC’s crystallization (Miyamoto et al. , 2014). In another work, in order to produce colored BC nonwovens, different natural and artificial dyes were added to the culture medium. Colors were successfully incorporated into the BC when natural dyes and the blue artificial dye were used, while other artificial dyes inhibited BC growth (Wood, Hang and Salusso, 2015). Shoe prototypes were developed using bacterial cellulose mats and the colors of the BC sheets were obtained by dyeing BC with red onion skins and coffee grounds leftovers (Nam and Lee, 2016). The dyeability of BC produced under static culture using in situ and ex situ methods was also studied using direct acid
Chapter 2 – Literature overview 31 and reactive dyestuffs. Although only the lower half of the BC was colored during the cultivation ( in situ method), after drying it showed uniform color on both sides and presented clearer colors when compared with the dried BC colored by the ex situ method (Shim and Kim, 2019). An environmentally friendly process was developed for the bio-coloration of BC via phenolic oxidation by laccase immobilized onto BC. Specifically, flavonoids were successfully polymerized by the immobilized laccase, which gave rise to yellow, orange and dark brown oligomers that colored the BC. Best results were obtained with the flavonoids catechol and catechin (Song et al. , 2018). BC films were also dyed by immersion of BC into plant-based natural dye ( Clitoria ternatea L. and Hibiscus rosa-sinensis ) solutions, while retaining the crystallinity, thermal and mechanical properties of BC (Costa et al. , 2019). Table 12. BC purification, bleaching, and dyeing. Study type Methodology Results Reference Purification and bleaching Cultivation of BC using HS medium for 8 days. Washing with NaOH and bleaching with different concentrations of H2O2. 3% NaOH better removal of impurities. 5% H2O2 increased the whiteness (white index 73). Crystallinity increased 27% after three-step process. (Han, Shim and Kim, 2019) Purification BC production in a coconut water-based culture medium with 10% of Acetobacter xylinum inoculum, in static conditions for 7 days. Washing with water and purification by soaking (24 h) with different percentages of NaOH (0–2%). Washing with water until neutral pH and air drying at 120 ºC. With higher % NaOH better removal of impurities, increment on the yield, thickness, and WVP of the BC. NaOH ≥ 2% WVP decreased. (Kamal, Misnon and Fadil, 2020) Dyeing (in-situ) Production of BC with 0–0.5 wt% of dyestuffs (direct, acid, and basic) dispersed into the culture media, by shaking for 24 h. Filtration and purification with NaOH solution, followed by neutralization, filtration, and freezedrying. Samples obtained with 0.5 wt% dyestuffs were washed with ethanol. Direct and basic dyestuffs stain BC but acid dyestuff did not. Direct dyestuffs inhibited the crystallization of BC, while basic dyestuff had almost no influence on it. (Miyamoto et al. , 2014) Dyeing (natural and synthetic dyes) Production of BC with natural dyes (turmeric, saffron, and beet) and artificial dyes (red, orange, yellow, green, blue, and violet) in the culture media, for 3 weeks. Drying at ambient conditions. Natural dyes and the blue artificial dye were incorporated into BC. The addition of the rest of the artificial dyes inhibited BC growth. (Wood, Hang and Salusso, 2015)
Chapter 2 – Literature overview 32 Shoe prototypes Dyeing of BC with red onion skins and coffee grounds leftovers Dark red and dark brown BC. (Nam and Lee, 2016) Dyeing (in-situ and exsitu methods) In situ dyeing by production BC with direct, reactive, and acid dyes and different carbon sources in the culture media, in the static condition, for 8 days, followed by washing with 3% NaOH and neutralization. Ex situ dyeing of BC with different temperatures and pH, for 30 min. Drying at 35 °C for 24 h. In situ method - highest production yield using glucose as a carbon source and reactive dye. Ex-situ method - best results for dyeing BC produced with fructose with reactive dye, at 135 °C, and pH 3. In situ method allows a smoother surface and higher color strength than the ex situ . (Shim and Kim, 2019) Dyeing (flavonoids) Production of BC in static condition for 8 days, followed by washing with distilled water and bleaching with H2O2 solution. Swelling with NaOH solution and drying. Immobilization of laccase into BC by immersion, at room temperature and 4 °C, for 12 h. Laccase‑mediated polymerization with catechol, catechin, ferulic acid and hydroquinone monomers by immersion overnight, followed by washing and drying. Color depth is more pronounced in samples with laccase immobilized at 4 °C and increases with the incubation time. Catechol and hydroquinone gave rise to a dark brown and catechin and ferulic acid to yellow-orange. (Song et al. , 2018) Dyeing (natural dyes) Production of BC in static condition for 10 days, followed by washing with tap water and purification with NaOH, and neutralization. Dyeing by immersion in a heated solution of natural pigments (extracted from Clitoria ternatea L. and Hibiscus rosa-sinensis) and mordants, for 30 min, followed by immersion in a solution containing 1% fixer and 2% of softener, for 15 min. Submersion in distilled water for 5 days led to a reduction in fixation of 28.3% for the Clitoria ternatea L. dye and a 12.1% reduction for the Hibiscus rosa-sinensis dye. After the hand washing simulation, the color intensity decreases. Loss in mechanical properties after dyeing. (Costa et al. , 2019) 2.5. Vegetable oils Vegetable oils (VOs) are renewable resources abundantly available with an increasing number of industrial applications that offer advantages such as low cost, non-toxicity, and biodegradability (López and Santiago, 2013; Saithai et al. , 2013). Basically, these raw materials are composed of triglyceride molecules, whose main components are fatty acids (three) linked to glycerol esters. Fatty acids in the most common triglycerides, range from 14 to 22 carbons in length and have 0 to 3 double bonds (Khot et al. , 2001; Lu and Wool, 2004; López and Santiago, 2013). To increase their reactivity, double bonds can be replaced by more reactive functional groups using chemical reactions, such as epoxidation,
Chapter 2 – Literature overview 33 acryloylation, hydroxylation, or maleinization (Grishchuk and Karger-Kocsis, 2011; Saithai et al. , 2013; Senoz et al. , 2013; Gandini and Lacerda, 2015). VOs and their derivatives are already used in different areas, such as health and cosmetics, biodiesel, paints, varnishes and coatings for wood, and anticorrosion agents for metals (López and Santiago, 2013). Among VOs, soybean oil is one of the most attractive due to its low price and abundant availability. Generally, their double bonds are epoxidized and then acryloylated, by reaction with carboxylic groups of acrylic acids, allowing their polymerization by free radicals (Gandini and Lacerda, 2015; Liu, Madbouly and Kessler, 2015). Acrylated epoxidized soybean oil (AESO) has been studied extensively in the production of composites with a high content of renewable resources. In general, these composites include different particles or fibers, such as microcrystalline cellulose (W. Liu et al. , 2017), regenerated cellulose fibers (Ramamoorthy et al. , 2014), coconut residues (Kocaman et al. , 2017), discarded cotton/polyester and denim fabrics (Ramamoorthy et al. , 2018; Temmink, Baghaei and Skrifvars, 2018), ramie fibers (Lee et al. , 2013), hemp fibers (Khot et al. , 2001; Akesson, Skrifvars and Walkenström, 2009; Liu et al. , 2018), flax and glass fibers (Khot et al. , 2001), or pyrolyzed fibers from chicken feathers (Senoz et al. , 2013). Regarding the area of leather and analogues, AESO has been tested in goatskin leather finish. Compared to untreated leather, coated leather showed a reduction in the friction coefficient on the inner face, thus showing the possibility of using AESO as an ecological solution for leather finishing (Nunez, Santiago and Lopez, 2008). A recent patent (Wool, 2013) demonstrates the possibility of making ecological leather analogues; the process consists of mixing natural fibers with different types of epoxidized and acryloylated triglycerides. According to the patent, different vinyl monomers and a catalyst can be added to this mixture. The composite is then deposited in appropriate molds and subjected to hot pressing techniques such as Resin Transfer Molding or Sheet Compound Molding. In another work, an environmentally friendly substitute for leather was developed by reinforcing a mixture of AESO resin with cotton fabrics (Cao et al. , 2013). Later, it was used for the development of ecological shoes composed of organic cotton fabrics and AESO/MLAU resin (lauryl methacrylate) (50/50). The prototype comprising this composite was applied to the upper part of the shoe and tested on volunteers. Its performance was evaluated using a questionnaire where the participants described it as wearable, versatile, and practical. Despite presenting this product as water-resistant and breathable, tests have not been carried out to measure these properties (Cao et al. , 2014). It is expected that by combining BC membranes, which have the unique properties already presented, with a biodegradable polymer, such as the AESO, it is possible to produce a truly green nanocomposite. In the literature, the works that have been developed with BC and modified soybean oil have a different
Chapter 2 – Literature overview 34 approach from the one intended in this research project. Highly porous UV curable and thermosetting nanocomposite foams from BC/AESO were developed by producing water-in-oil emulsions stabilized by BC nano-fibrils previously hydrophobized by acetylation and silylation (Blaker et al. , 2009). In another work, other monomers were added to AESO and the emulsions were polymerized by free radicals (Sousa et al. , 2017). It was also shown that it is possible to produce macroporous 3D polymers through microwave heating of liquid gas/AESO foams. The addition of BC allowed to significantly improve the stability of the foams, by obstructing the flow of liquid, and the mechanical properties, since it acts simultaneously as a nanofiller (Koon-Yang Lee et al. , 2011). Optically transparent composites with excellent mechanical properties were developed by impregnating BC films with epoxidized soy oil. To improve the dispersion of the nanofibers and the adhesion between the cellulose and the hydrophobic polymeric matrix, pressed BC films were acetylated (Retegi et al. , 2012).
35 Chapter 3 Development of BC/PDMS/PFC composites 1 3.1. Abstract This research aimed at obtaining a malleable, breathable and water impermeable bacterial cellulosebased nanocomposites, by impregnating bacterial cellulose (BC) membranes with two commercial hydrophobic polymers used in textile finishing, Persoftal MS (polydimethylsiloxane (PDMS)) and Baygard EFN (perfluorocarbon (PFC)), by an exhaustion process. These hydrophobic products penetrated the BC membranes and adsorbed tightly onto the surface of the nanofibers, across the entire depth of the material, as demonstrated by scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy studies. The water static contact angles, drop absorption over time and vapor permeability values showed that the composites were impermeable to liquid water but permeable to water vapor. The mechanical properties of the BC-nanocomposites were improved after incorporation of the hydrophobic products, in some of the formulations tested, overall presenting a satisfactory performance. Thus, through a simple and cost-effective process, hydrophobized, robust, malleable and breathable nanocomposites based on BC were obtained, featuring promising properties for application in the textile and shoe industries. 1 This chapter is based on the following publication: Fernandes, M., Gama, M., Dourado, F. and Souto, A. P. (2019) “Development of novel bacterial cellulose composites for the textile and shoe industry,” Microbial Biotechnology , 12(4), pp. 650–661.
Chapter 3 – Development of BC/PDMS/PFC composites 36 3.2. Introduction Bacterial cellulose (BC) consists of a 3D nanofibrillar arrangement of pure cellulosic fibers with a diameter of 20-100 nm and several micrometers in length, resulting in a high specific surface area (Tang et al. , 2015; Wu et al. , 2016), property which are very advantageous for the production of composite materials (Lee, Blaker and Bismarck, 2009; Wan et al. , 2009; Wu et al. , 2016). BC also exhibits high crystallinity, high degree of polymerization, high water holding capacity and high moldability (Lee, Blaker and Bismarck, 2009). These unique properties have sustained the elevator pitch of several BC applications in the biomedical field, pulp & paper, composites and foods (Andrade et al. , 2010; Dourado et al. , 2016; Fortunato et al. , 2016; Gonçalves et al. , 2016; Padrão et al. , 2016). Despite these excellent properties, the loss of flexibility upon drying is a disadvantage for several applications such as in the textile and shoe industry. Due to the collapse of the 3D nanofibrillar BC network, a significant reduction in gas permeability also occurs, heavily reducing the material’s breathability. Further, the hydrophilic nature of BC hinders the combination with hydrophobic polymer matrixes, an obstacle to the development of composites where both BC and the added polymer contribute to the final desirable properties. Several studies have been conducted on the chemical modification/hydrophobization of cellulose and of BC in particular, attempting to overcome these issues (Tomita, Tsuji and Kondo, 2009; Nisoa and Wanichapichart, 2010; Tomé et al. , 2010; Wan et al. , 2017). The major limitations of ex situ BC modification methods concern with the size and nature of the reinforcing materials, namely, only soluble polymers and nano-submicron sized materials can penetrate into the BC 3D network. The bulk distribution of these particles within the BC pellicle is also heterogeneous, a feature further aggravated by the hydrophobic nature of certain polymer matrices, which have poor interfacial adhesion to native BC (Shah et al. , 2013). Throughout this research, a novel approach was tested for the bulk and surface modification of BC, combining simplicity, potential for application at large scale and low cost, based on the use of an exhaustion process. Through this process, two hydrophobic commercial polymers, Persoftal MS Con.01, a softener based on polydimethylsiloxane (PDMS), and Baygard EFN, a hydrophobizer based on perfluorocarbon (PFC), were incorporated into the nanofibrillar matrix of BC, aiming at obtaining a malleable, breathable and water impermeable nanocomposite with strong potential of application in textile and shoe industries.
Chapter 3 – Development of BC/PDMS/PFC composites 37 3.3. Materials and methods 3.3.1. Materials BC membranes were offered by Satisfibre S.A. (Portugal). The commercial polymer formulations, Persoftal MS Conc.01 (a softener based on Polydimethylsiloxane - PDMS) and Baygard EFN (hydrophobizer based on Perfluorocarbon - PFC), both from Tanatex Chemicals, were offered by ADI Center Portugal. Perfluorinated acrylate polymers have extremely low surface energy due to their side chain containing outwardly oriented perfluoro hydrophobic groups and are widely used in textile and leather coatings. The application of perfluorinated organic compounds with a long perfluoroalkyl chain (CnF2n+1, n ≥ 8) has been restricted by the European Union due to its high bioaccumulation and difficult biodegradation (Zahid et al. , 2017). Thus, the hydrophobic product used in this work consisted of a C6-based Fluorocarbon polymer nano-emulsion without Perfluorooctane Sulfonate (PFOS) and less than 5 ppb Perfluorooctanoic Acid (PFOA). The characteristics of the products used are summarized in Table 13. Table 13. Characteristics of the finishing polymers used.a Softener (S) – Persoftal MS Conc.01 Hydrophobizer (H) – Baygard EFN Chemical basis Modified polysiloxane aqueous dispersion Fluorocarbon polymer aqueous nano-emulsion Ionicity Non-ionic Non-ionic Density 0.99 g·cm−3 (23°C) 1.1 g·cm−3 (20°C) Viscosity 405 mPa·s (23°C) 100 mPa·s (20°C) Content 10–20% Siloxanes and Silicones, 3-((2aminoethyl)amino)propyl Me, diMe, hydroxyterminated (CAS: 75718-16-0) 3–5% Alcohols, C12-18, ethoxylated (CAS: 68213-23-0) 3–5% Alcohols, C10-14, ethoxylated (CAS: 66455-15-0) 0.1–1% Octamethylcyclotetrasiloxane (CAS: 556-67-2) 28% Fluorocarbon polymer 0.1–1% Alcohols, C16-20, ethoxylated (CAS: 106232-82-0) a Information extracted from the technical sheets provided by the manufacturer.
Chapter 3 – Development of BC/PDMS/PFC composites 38 3.3.2. Composites production BC membranes (with about 2.5–3.0 cm in thickness, with a size of 12.0 × 13.0 cm and weighting 450 g) were squeezed to a final wet mass of 100 g (2.6% BC (w/w)). The compressed membranes were each treated by exhaustion in 100 mL of: i) an aqueous mixture containing either the softener (S) or the hydrophobizer (H), each, at different concentrations (1, 10, 25, and 50% (v/v)), or; ii) processed in two steps by exhaustion with 10, 25 and 50% (v/v) of softener S, followed by drying; afterwards, the dried composites were each impregnated with 50% (v/v) hydrophobizer H (further designated by 10S + H, 25S + H, and 50S + H). It is expected that with the sequential application S+H a material with suitable properties for application in the textile and shoe industry can be achieved. Considering PDMS characteristics, it allows properties such as malleability, robustness and softness, permitting water vapor transmission. However, since the hydroxyl and amino-functional polar groups linked to PDMS in the softener used impart some hydrophilicity, the subsequent application of the PFC nano-emulsion will hydrophobize the surface. The exhaustion process was carried out in an Ibelus machine equipped with an infrared heating system, using stainless-steel cups with a capacity of approximately 220 cm3, with a rotation of 50 rpm and 40 cycles. The desired temperature (30 °C) was achieved using a gradient of 2 °C·min-1. The treatment lasted for 5 days at 30 °C, after which the samples were oven dried (WTC binder oven) at 25 °C for 48 hours, followed by a curing step for 30 min at 120 °C. To avoid shrinkage of the samples during drying and curing, the composite BC membranes were attached to a zinc-plated wire support. 3.3.3. Physical-chemical properties evaluation 3.3.3.1. Scanning electron microscopy (SEM) BC composites were coated with a thin layer of gold-palladium. Analyses of the surface morphology and cross section of these composites were done using an ultra-high-resolution field emission gun SEM instrument (NOVA 200 Nano SEM, FEI, Hillsboro, OR, USA).
Chapter 3 – Development of BC/PDMS/PFC composites 39 3.3.3.2. Atomic force microscopy (AFM) Atomic force microscope images of the BC composites were collected in tapping mode using a Nanoscope III microscope from Digital Instruments (Santa Barbara, CA, USA), with antimony-doped silicon probes in contact mode in air. Images were captured at a scanning rate of 1.0 Hz and resolution of 512 pixels × 512 pixels. The roughness parameters, roughness average (Ra) and root mean square (RMS), were calculated using the average of three scans in different places for each sample in 10 μm × 10 μm area. 3.3.3.3. Fourier transform infrared (FT-IR) analysis A Nicolet Avatar 360 FT-IR spectrophotometer (Madison, WI, USA) was used to record the FT-IR spectra of the BC sheet and BC composites. The spectra were collected in the attenuated total reflection mode (ATR) at a spectral resolution of 16 cm−1, with 60 scans, over the range 400–4000 cm−1 at room temperature. A background scan with no sample and no pressure was acquired before the spectra of the samples were collected. 3.3.3.4. Surface energy Contact angles measurements were carried out in a Dataphysics instrument (Filderstadt, Germany) using OCA20 software (Germany) with a video system for the capture of images in static mode using the sessile drop method. A drop of 5 µL of distilled water was placed on the composite’s surface with a microliter syringe and observed with a special charge-coupled device camera. After a water drop was deposited in the composites surface, the water contact angle was observed over time for 220 s. At least five measurements at different places were taken for each sample. The camera recorded an image every 0.04 s. To calculate the surface energy (γs) of the BC and the polar (γsP) and dispersive (γsD) components, the Wu method (harmonic-mean) was used, with the Equation (1) (Wu, 1971): γ𝑠𝑙 = γ𝑠+ γ𝑙− 4 [ γ𝑠 𝐷γ𝑙 𝐷 γ𝑠 𝐷+ γ𝑙 𝐷+ γ𝑠 𝑃γ𝑙 𝑃 γ𝑠 𝑃+ γ𝑙 𝑃] , (1) The following liquids (𝑙) with known surface energy and surface energy components were used: distilled water (γ: 72.8; γD: 29.1; γP: 43.7); polyethylene glycol 200 (γ: 43.5; γD: 29.9; γP: 13.6); and glycerol (γ: 63.4; γD: 37.4; γP: 26.0), units in mJ·m−2 (Oliveira et al. , 2013).
Chapter 3 – Development of BC/PDMS/PFC composites 46 matter of fact, the BC fibres are well coated with S in the series of samples impregnated with 1% up to 50%, as observed by SEM; thus the differences observed cannot be assigned to surface chemistry only. Table 15. Average contact angle values (°) measured for drops of water, PEG 200 and glycerol. Sample Water PEG 200 Glycerol BC 63.8 ± 4.7 38.3 ± 2.3 105.0 ± 4.1 BC-1S 126.2 ± 1.9 108.1 ± 2.2 126.4 ± 1.1 BC-10S 129.2 ± 0.5 115.2 ± 3.0 129.4 ± 1.3 BC-25S 128.4 ± 2.1 108.0 ± 2.8 125.3 ± 1.3 BC-50S 115.0 ± 4.4 98.4 ± 0.7 112.3 ± 1.5 BC-1H 89.4 ± 5.2 66.5 ± 1.7 125.7 ± 1.7 BC-10H 131.2 ± 2.7 101.2 ± 3.8 123.6 ± 2.7 BC-25H 128.3 ± 0.8 101.1 ± 1.0 127.3 ± 3.8 BC-50H 125.8 ± 2.5 101.5 ± 1.7 122.4 ± 3.3 BC-10S + H 135.4 ± 1.0 113.4 ± 1.8 124.7 ± 3.4 BC-25S + H 134.8 ± 1.0 117.4 ± 1.6 128.3 ± 1.1 BC-50S + H 127.6 ± 2.5 112.3 ± 0.9 123.7 ± 1.6 Despite the overall proximity in the values of the static contact angles between S and H composites, the later showed lower permeability to water, as observed from the significantly slower water absorption rates over time (Figure 6a and b). As a matter of fact, the use of H seems to provide water resistant properties more effectively. The reason for this clear trend is not obvious, taking in account the static contact angle or the surface energy (as discussed ahead), and may be related to the ultrastructure, namely porosity, of the composites.
Chapter 3 – Development of BC/PDMS/PFC composites 47 Figure 6. Contact angles over time of the BC composites produced with S (a), H (b), with S and H applied sequentially, and BC (c). 0 20 40 60 80 100 120 140 020 40 60 80 100 120 140 160 180 200 220 Contact angle (°) Time (seconds) BC-1S (θi=126.2˚) BC-10S (θi=129.2˚) BC-25S (θi=128.8˚) BC-50S (θi=115.0˚) 0 20 40 60 80 100 120 140 020 40 60 80 100 120 140 160 180 200 220 Contact angle (°) Time (seconds) BC-1H (θi=89.4˚) BC-10H (θi=131.2˚) BC-25H (θi=128.3˚) BC-50H (θi=125.8˚) 0 20 40 60 80 100 120 140 020 40 60 80 100 120 140 160 180 200 220 Contact angle (°) Time (seconds) BC-10S + H (θi=135.4˚) BC-25S + H (θi=134.8˚) BC-50S + H (θi=127.6˚) BC (θi=63.1˚) (a) (b) (c)
Chapter 3 – Development of BC/PDMS/PFC composites 48 The surface energy is an important variable to understand the wetting phenomena and can be determined from the measurement of the contact angles formed by liquids with different surface energies. Wu’s approach (Wu, 1971) was used in this study for monitoring the surface energy and its components on the BC composites. The polar and dispersive components of the surface free energy of unmodified BC and the BC composites are displayed in Figure 7. The results show that, overall, comparatively to BC, BC composites obtained by treatment with S or H and by sequential impregnation (S+H) had a noticeable decrease in the surface free energy, due to the reduction of the polar component. Figure 7. Total surface energy, dispersive and polar components, determined with the Wu method, using the initial contact angles of water, PEG 200 and glycerol. 3.4.5. Water vapor permeability (WVP) and static water absorption (SWA) Breathability of textiles and leather products is commonly assessed through the measurement of water vapor permeability. This is very important for proper moisture management and to ensure the thermophysiological comfort of the human body. An adequate skin temperature balance must be achieved through perspiration and breathability (Tang, Kan and Fan, 2014; Mukhopadhyay, Preet and Midha, 2018). As observed in Figure 8, the WVP values of the BC composites decreased when compared to the original dry BC. However, all BC composites were still breathable. Indeed, according to the technical report 0 10 20 30 40 Surface free energy (mJ·m−2) Total surface free energy Dispersive Polar
Chapter 3 – Development of BC/PDMS/PFC composites 49 ISO/TR20879 (ISO, 2007), that establishes the WVP performance requirements for upper footwear components, most of the composites are suitable to be used in footwear (casual footwear - WVP ≥ 192 g·m−2·24 h−1). Also, with an increase in the amount of incorporated S or H, (as observed by the increase in the mass per unit area (Figure 8) and thickness (Table 18)) a decrease in the WVP was observed, as could be expected. In general, the sequential treatment using both polymers did not change significantly the WVP values, as compared to BC samples treated only with the softener. Figure 8. Water vapor permeability and mass per unit area. The comfort of clothing and footwear is closely associated with both water vapor permeability and static water absorption. In the case of footwear, sweat is first absorbed by the lining and insole material and then the moisture is transferred to the exterior. The materials used inside the shoe should therefore have a good level of water absorption so that the sweat does not accumulate, causing discomfort. The recommended water absorption is a maximum of 60% after 120 min for uppers and a minimum of 100% for linings and insoles (Bitlisli et al. , 2005). The static water absorption was in this work measured at 15, 30, 60 and 120 min. The results are shown in Figure 9. The composites with higher amounts of added polymers (50S, 50H and 50S + H) absorbed less than 60% of water after immersion for 120 min, thus being appropriate for uppers, whereas most of the other composites show an absorption higher than 100% and are more suitable to be used in linings and insoles. 0 100 200 300 400 500 0 100 200 300 400 500 Mass per unit area (g·m−2) Water vapor permeability (g·m−2·24 h−1) Water vapor permeability Mass per unit area
Chapter 3 – Development of BC/PDMS/PFC composites 50 Figure 9. Static water absorption. 3.4.6. Mechanical properties The characterization of the mechanical properties resulting from the tensile test are shown in Table 16. The tensile strength and elongation break of dried BC was found to be of 35.60 MPa and 3.44%, respectively. Incorporation of increasing amounts of S or H increased the thickness and the mass per unit area of the composites, while decreasing the WVP. Unexpectedly, the mechanical properties of the composite did not follow this progression. Regarding the incorporation of softener, maximum tensile strength values were of 42.64 MPa (1S), whereas the maximum elongation at break observed was 7.67% (50S). As for the hydrophobizer, the maximum values of tensile strength and elongation at break were observed, respectively, for 10% and 25% of polymer impregnation. As observed by SEM, the BC composites with lower amounts of polymer absorbed formed thicker fibers. Additionally, the high interfacial interaction between the added polymers and the cellulose nanofibers through hydrogen bonding allows an efficient distribution of the stress, resulting in an improvement of the mechanical properties. However, as the concentration of the added products increase, the tensile strength and Young modulus start to decrease. This observation can be explained by the complete coating of surface hydroxyl groups of the cellulose nanofibers, preventing their contribution to the mechanical strength and elasticity through H-bonding. As previously reported (Soykeabkaew et al. , 2009; Gea et al. , 2010; Asgher, Ahmad and Iqbal, 2017), the strong attractive hydrogen bonding between cellulose nanofibers tends to weaken owing to extensive surface coating, affecting negatively the mechanical properties. In our composites, the quantity of BC (reinforcement) is constant. As more polymers (matrix) are incorporated, the relative 0 20 40 60 80 100 120 140 Static water absorption (%) 15 min 30 min 60 min 120 min
Chapter 3 – Development of BC/PDMS/PFC composites 51 percentage of the reinforcement decreases, the behavior of the composite becoming increasingly governed by the matrix. Therefore, the mechanical strength and elasticity of the composite becomes gradually dependent on the intermolecular bonding of the matrix polymers. In the case of the softener polydimethylsiloxane, the weak intermolecular forces between the methyl groups yield very low tensile strength (Paquien et al. , 2005; Jin et al. , 2018). Also, fluorine atoms have low polarizability that results in low surface energies and thus weak cohesive forces between fluorocarbon molecules (Lemal, 2004). It is also observed that samples with higher amounts of incorporated polymers have higher elongation, due to the greater mobility allowed between the different layers of the BC membrane. Finally, no significant differences were achieved by sequentially incorporating H in samples pretreated with S. Overall, taking as reference the technical report ISO/TR20879 (ISO, 2007), that establishes the performance requirements for uppers components for footwear, the composites present suitable mechanical properties [casual footwear – Breaking strength ≥ 10 N·mm-1, elongation ≥ 7% (along)]. Regarding tensile strength, all samples are above or near the reference value, although regarding the elongation at break only 50S, 25H and 25S + H samples match the requirements. Table 16. Thickness, Young’s modulus, tensile strength, and elongation at break. Sample Thickness (mm) Young’s modulus (MPa) Tensile strength (MPa)a Elongation at break (%) BC 0.30 ± 0.01 9.19 ± 0.30 35.60 ± 3.10 3.44 ± 0.08 BC-1S 0.34 ± 0.01 18.38 ± 6.15 42.64 ± 7.26 3.45 ± 0.82 BC-10S 0.48 ± 0.03 6.14 ± 0.78 35.61 ± 2.59 5.10 ± 0.17 BC-25S 0.63 ± 0.04 1.57 ± 0.28 27.18 ± 1.40 6.90 ± 1.55 BC-50S 0.73 ± 0.02 1.35 ± 0.50 16.31 ± 0.26 7.67 ± 0.27 BC-1H 0.30 ± 0.01 23.10 ± 2.37 40.04 ± 10.36 2.82 ± 0.73 BC-10H 0.34 ± 0.02 11.72 ± 1.56 48.35 ± 8.80 5.92 ± 0.83 BC-25H 0.50 ± 0.02 3.90 ± 0.21 27.78 ± 0.77 7.97 ± 0.65 BC-50H 0.61 ± 0.08 3.35 ± 0.85 25.46 ± 2.18 6.04 ± 0.39 BC-10S + H 0.37 ± 0.02 5.17 ± 0.38 37.25 ± 3.92 5.48 ± 0.29 BC-25S + H 0.53 ± 0.02 3.37 ± 0.90 31.78 ± 6.71 8.94 ± 0.95 BC-50S + H 0.77 ± 0.03 2.32 ± 0.62 17.29 ± 0.63 6.37 ± 0.72 First set: 1S/25S; BC/50S; 1S/50S; 10S/50S; 25S/50S; Second set: 10H/25H; 10H/50H; Third set: BC/50S + H; 10S + H/50S + H; 25S + H/50S + H. a Multiple comparison tests between BC and each set of composites, means difference is significant at the 0.05 level.
Chapter 3 – Development of BC/PDMS/PFC composites 52 3.5. Conclusion In this study, through an exhaustion process, BC fibers were surface modified with Persoftal MS Con.01 and Baygard EFN, resulting in malleable and mechanically resistant composites, with hydrophobic character and breathability. The new BC-based composites may offer a sustainable alternative to cotton, leather and man-made cellulosic fibers, thus exhibiting strong potential for further high value-added differentiation and sustainable consumer products such as textiles and leather. BC-based composites may be regarded as strategic materials with enormous potential, focusing on natural and organic products development and represent an alternative to materials used today in textile and shoe industries.
53 Chapter 4 Development of BC/PDMS/PEG/AESO composites 2 4.1. Abstract Bacterial cellulose (BC) obtained by static culture was used to produce bio-based composites. A mixture of an amino-polydimethylsiloxane-based (PDMS) softener, polyethyleneglycol (PEG) 400 and acrylated epoxidized soybean oil (AESO), was incorporated into the BC membranes through an exhaustion process. The results show that BC composites with distinct performances can be easily designed by simply varying the polymers percentage contents. This strategy represents a simple approach towards the production of BC-based composites. 2 This chapter is based on the following publication: Silva. F. A. G. S., Fernandes, M., Souto, A. P., Ferreira, C., Dourado, F. and Gama, M. (2019) “Optimization of bacterial nanocellulose fermentation using recycled paper sludge and development of novel composites,” Applied Microbiology and Biotechnology , 103(22), pp. 9143–9154.
Chapter 4 – Development of BC/PDMS/PEG/AESO composites 54 4.2. Introduction Acrylated epoxidized soybean oil (AESO) is obtained from soybean oil, a renewable resource abundantly available, via epoxidation and acryloilation. It contains three highly reactive functionalities, double (C=C) bonds, –OH groups, and epoxy rings. The C=C bonds in AESO is capable of self-polymerizing and copolymerizing with other components via a free-radical initiation, forming a three-dimensional network (Liu et al. , 2018). Bacterial cellulose (BC) membranes were used for the development of nanocomposites, using formulations that includes: (i) a commercial softener based on polydimethylsiloxane (PDMS) (conferring malleability, robustness and softness); (ii) polyethyleneglycol (PEG) 400 (as a plasticizer, allowing to obtain a product with greater elasticity as well as contributing to improve the interfacial adhesion between the BC and the other polymers) and (iii) acrylated epoxidized soybean oil (AESO) (yielding a high biobased content BC composite with hydrophobic character). A simple and effective approach was developed, based on the use of an exhaustion process, aiming to produce BC nanocomposites. 4.3. Materials and methods 4.3.1. Materials BC membranes were offered by Satisfibre S.A. (Portugal). Soybean oil, epoxidized acrylate (Sigma-Aldrich, Steinheim, Germany), Lauryl methacrylate (97%) (Acros Organics, Geel, Belgium), 1,6hexanodiol diacrylate (80%) (Sigma-Aldrich, Steinheim, Germany), Tri (propylene glycol) diacrylate (SigmaAldrich, Steinheim, Germany), tert-Butyl peroxybenzoate (98%) (Sigma-Aldrich, Steinheim, Germany), Polyethylene glycol 400, (Merck Millipore, Darmstadt, Germany), were used as received without further purification. The softener Persoftal MS Conc.01 (Tanatex Chemicals) consists of an non-ionic aqueous dispersion of Siloxanes and Silicones, 3-((2-aminoethyl)amino)propyl Me, diMe, hydroxy-terminated (1020%), with density of 0.99 g·cm-3 (23 °C) and viscosity of 405 mPa·s (23 °C). 4.3.2. Composites production BC membranes were used as a scaffold for the production of composites by the incorporation of a mixture of Persoftal MS Conc.01 (PDMS-based polymer), PEG 400 and the resin AESO. AESO has a low cross-linking density and thus inferior mechanical strength due to the existence of long aliphatic chains
Chapter 4 – Development of BC/PDMS/PEG/AESO composites 55 and low degree of unsaturation in AESO molecules. Also, it has high viscosity at room temperature that restricts its processability (Liu et al. , 2018). To reduce these limitations, a mixture containing different reactive monomers added to AESO (coded “AESO mixture”, Table 17), was prepared as follows (in mass percentages): AESO (50%), lauryl methacrylate (38.5%), 1,6-hexanodiol diacrylate (5%), tri(propylene glycol) diacrylate (5%), and the initiator tert-Butyl peroxybenzoate (1.5%). This mixture was prepared 24 h prior to use where all products were mixed and then placed under magnetic stirring for 1 h at 500 rpm. For the composites’ production, purified wet BC membranes with about 3.0 cm in thickness, with a size of 13.0 × 16.0 cm and weighting 700 g were used. The membranes were first mechanically pressed to remove the excess of adsorbed water to a final wet mass of 135 g, corresponding to 5.5% dry mass in BC and a thickness of around 0.5 cm. The compressed membranes were then treated with the different polymers at different combination, by an exhaustion process, as detailed in Table 17. Table 17. Formulations used in the production of BC composites. Sample Persoftal MS (g) PEG 400 (g) AESO mixture (g) BC - - - BC-S 1 75 0 0 BC-S/PEG400 60 15 0 BC-S/PEG400/AESO 20 20 35 1 S: Softnener For this, the pressed BC membranes were placed inside the stainless-steel cups and the polymers’ mixture was added at a mass ratio of BC:polymer mixture of 1:10. The exhaustion process was then carried out in an Ibelus machine equipped with an infrared heating system, using stainless-steel cups with a capacity of approximately 220 cm3, with a rotation of 50 rpm, for 40 cycles. The desired temperature (60 °C) was achieved using a gradient of 2 °C·min-1. The treatment lasted for 2 days at 60 °C, after which the samples were oven dried (WTC binder oven) at 90 °C for 24 h (until constant mass), followed by a curing step for 3 h at 180 °C.
Chapter 4 – Development of BC/PDMS/PEG/AESO composites 62 4.4.4. Water vapor permeability (WVP) The breathability, expressed in water vapor permeability (WVP), of textile and leather materials is an important property to assure body comfort. As observed in Figure 13, the WVP values of the BC composites decreased when compared to the original dry BC. However, all BC composites were still breathable. In solid polymers, the water vapor permeation mechanism is determined by a sequencial process of adsorption/absorption, diffusion and desorption, first, water molecules adsorb onto the material’s surface, until an equilibrium is established. Then the water molecules diffuse througth the material driven by a concentration gradient and finally desorption occurs from the opposite surface (Lu, Tian et al. 2016). As shown by the results, water vapor could easily permeate through pure BC. Cellulose is strongly hydrophilic and although the molecular chains pack tight together after drying, water molecules can easily interact with the abundant hydroxyl groups on the cellulose molecules through hydrogen-bonds followed by diffusion (Li, Zhou et al. 2019). When modified amino-PDMS was incorporated into the BC matrix, the WVP values decreased noticeably. This composite presents better water resistance when compared with cellulose, affecting the adsorption process. In contrast, the addition of PEG400 to BC-S composite, increased WVP value due to its hydrophilic character. Although AESO has a hydrophobic character, there is an increase WVP. As observed from SEM, BC-S/PEG400/AESO composite possesses an irregular structure along its cross-section. We can speculate that some incompatibility between the polymers leds to the formation of aglomerates, creating more free volume and relative short pathway for water molecules to diffuse. Figure 13. Water vapor permeability of BC and BC composites. 289.56 51.78 83.21 149.78 0 50 100 150 200 250 300 350 BC BC-S BC-S/PEG400 BC-S/PEG400/AESO Water vapor permeability (g·m−2·24 h−1)
Chapter 4 – Development of BC/PDMS/PEG/AESO composites 63 4.4.5. Mechanical properties SEM and FT-IR analysis of the composites suggest that a good interfacial adhesion between the polymers mixture and BC was achieved. Despite the high amounts of the polymers impregnated (Table 18), the behavior of the composite is also governed by the BC matrix. Compared to BC, the mechanical properties of the composites were dramatically reduced, as shown in Figure 14. The biggest obstacle for the practical application of composites is the poor stress transfer between the reinforcement and polymer matrix. Generally, the stress transfer between the two phases is strongly dependent on the degree of interfacial bonding (Wei and Mcdonald, 2016). So, a lower tensile strength than that of neat BC was expected, as PDMS is an amorphous polymer and BC membrane is a highly crystalline material; also, the addition of other polymers to BC membrane detracts the inter-molecular hydrogen bonds between the BC fibers, decreasing the tensile strength of the composite. The introduction of PEG did not significantly improve the tensile strength but the elongation at break increased noticeably. PEG can act as a plasticizer, providing more space between the BC fibers. On the other hand, when the AESO mixture was added, and since it was well dispersed in the matrix and, probably a better fiber-matrix interface bonding was formed, restricting the motion of PDMS molecule chains, which increased the stress transfer, resulting in a composite with higher tensile strength. Figure 14. Stress-strain averaged curves of BC and BC composites obtained up to the rupture point 0 5 10 15 20 25 30 35 40 0 2 4 6 8 10 12 14 16 Stress (MPa) Strain (%) BC 37.5 MPa 3.62% BC-S 4.06 MPa 3.03% BC-S/PEG400 3.48 MPa 11.06% BC-S/PEG400/AESO 6.87 MPa 9.07%
Chapter 4 – Development of BC/PDMS/PEG/AESO composites 64 4.5. Conclusion New BC-based composites with a high degree of sustainability were successful produced through exhaustion with modified amino-PDMS, PEG 400 and AESO. FT-IR and SEM analyses provided evidence of the incorporation of these polymers into the BC membrane, resulting on its hydrophobic performance. Although BC has been used for the reinforcement of composites by several authors, there are very few studies using the intact BC membrane obtained by static fermentation, thus keeping intact the 3D BC network.
65 Chapter 5 Development of BC/emulsified AESO composites 3 5.1. Abstract This research investigated the development of bio-based composites comprising bacterial cellulose (BC), as obtained by static culture, and acrylated epoxidized soybean oil (AESO) as an alternative to leather. AESO was first emulsified; polyethylene glycol (PEG), polydimethylsiloxane (PDMS) and perfluorocarbonbased polymers were also added to the AESO emulsion, with the mixtures being diffused into the BC 3D nanofibrillar matrix by an exhaustion process. Scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy analysis demonstrated that the tested polymers penetrated well and uniformly into the bulk of the BC matrix. The obtained composites were hydrophobic and thermally stable up to 200 °C. Regarding their mechanical properties, the addition of different polymers lead to a decrease in the tensile strength and an increase in the elongation at break, overall presenting satisfactory performance as a potential alternative to leather. 3 This chapter is based on the following publication: Fernandes, M., Souto, A. P., Gama, M. and Dourado, F. (2019) “Bacterial cellulose and emulsified AESO biocomposites as an ecological alternative to leather,” Nanomaterials , 9(12), pp. 1710–1727.
Chapter 5 – Development of BC/emulsified AESO composites 66 5.2. Introduction The tannery industry faces several challenges associated with high environmental impact, scarcity of raw materials and increasing consumer demand for environmentally friendly products. The worldwide production of leather is approximately 20 billion square feet per year (FAO, 2015). To produce 1 ton of leather, 6.7 tons of raw skin (Kanagaraj et al. , 2015), 57,000 liters of water (Wool, 2013), and 3.35 tons of chemicals are required (Black et al. , 2013). Worldwide, for bovine skin, 370 billion liters of water are consumed annually, generating 6.5 million tons of solid waste. This research intends to contribute to the reduction of the animal hide dependency by the development of composites from bacterial cellulose (BC) as structuring material and activated vegetable oils as a flexibilizing, mechanical reinforcing and hydrophobizing agent. BC is a biopolymer produced by bacterial fermentation that consists exclusively of a three-dimensional structure of pure cellulose nanofibers. Chemically, BC is identical to vegetable cellulose but the nano-scale of its fibers offers a significantly higher surface area (Wang, Tavakoli and Tang, 2019). Vegetable oils (VOs) are abundant renewable resources with an increasing number of industrial applications. They offer the advantages of low cost, nontoxicity and biodegradability (Zhu et al. , 2004; Kim et al. , 2010; López and Santiago, 2013; Saithai et al. , 2013). Among the VOs, soybean oil is one of the most attractive due to its low price and abundant availability. To increase their reactivity, double bonds can be replaced by more reactive functional groups such as epoxide, acrylate, hydroxyl or maleate (Grishchuk and Karger-Kocsis, 2011; Saithai et al. , 2013; Senoz et al. , 2013; Gandini and Lacerda, 2015). Most commonly, double bonds are epoxidized and then acrylated, reacting with carboxyl groups of acrylic acids, allowing free radical polymerization (Gandini and Lacerda, 2015; Liu, Madbouly and Kessler, 2015). Acrylated epoxidized soybean oil (AESO) has been studied extensively in the production of composites with high renewable content (Khot et al. , 2001; Akesson, Skrifvars and Walkenström, 2009; Lee et al. , 2013; Senoz et al. , 2013; Ramamoorthy et al. , 2014, 2018; Kocaman et al. , 2017; Liu et al. , 2018; Temmink, Baghaei and Skrifvars, 2018). Regarding leather and analogues, AESO was surface-grafted onto goat leather using UV-radiation (Nunez, Santiago and Lopez, 2008). A recent patent (Wool, 2013) demonstrated the possibility of manufacturing ecological leather analogues by mixing natural fibers with epoxidized and acrylated triglycerides and vinyl monomers, the mixture being chemically polymerized. The composite was then deposited in suitable molds and hot pressed. In another work (Cao et al. , 2013), an environmentally friendly leather substitute was developed by reinforcing a mixture of AESO resin with
Chapter 5 – Development of BC/emulsified AESO composites 67 cotton fabrics. Later, an ecological leather composed of organic cotton fabrics and AESO/MLAU (methacrylated lauric acid) (50/50) resin was tested in footwear (Cao et al. , 2014). Although the authors presented this product as water-resistant and breathable, no tests were performed to support these claims. Composites of BC with modified soybean oil have also been reported, namely in the development of composite foams (Blaker et al. , 2009; Koon-Yang Lee et al. , 2011; Sousa et al. , 2017) and optically transparent composites (Retegi et al. , 2012). From the above, as is the purpose of this work, it is expected that by combining never dried BC membranes, as obtained by microbial fermentation, with a biodegradable polymer such as AESO, it may be possible to produce a truly green nanocomposite with potential applications in the leather industry. BC constitutes a three-dimensional polymeric structure with interconnected fibers, with macroporosity and therefore high aptitude to the anchorage of the AESO emulsified particles. Further, using emulsified VOs as low-cost natural substrates obviates the need to surface-modify BC, thus simplifying the preparation of BC-based composites while not affecting the BC’s native properties. This strategy represents a novel and promising approach towards the development of an environmentally friendly product, exclusively from biological and recyclable materials, at low water and energy production costs.
Chapter 5 – Development of BC/emulsified AESO composites 68 5.3. Materials and methods 5.3.1. Materials Bacterial cellulose membranes were offered by Satisfibre S.A. (Braga, Portugal). Soybean oil, epoxidized acrylate (Sigma-Aldrich, Steinheim, Germany), lauryl methacrylate (97%) (Acros Organics, Geel, Belgium), 1,6-hexanodiol diacrylate (80%) (Sigma-Aldrich, Steinheim, Germany), tri(propylene glycol) diacrylate (Sigma-Aldrich, Steinheim, Germany), Triton X-100 (Sigma-Aldrich, Steinheim, Germany), Span 80 (Sigma-Aldrich, Steinheim, Germany), isobutanol (Merck Millipore, Darmstadt, Germany), cumene hydroperoxide (80%) (Sigma-Aldrich, Steinheim, Germany), cobalt naphthenate (6%) (Sigma-Aldrich, Steinheim, Germany), and polyethylene glycol 400 (Merck Millipore, Darmstadt, Germany), were used as received. Persoftal MS Conc.01 and Baygard EFN (Tanatex Chemicals) were offered by ADI Center (Santo Tirso, Portugal). 5.3.2. Preparation of the acrylated epoxidized soybean oil (AESO) mixture AESO was used in this work to produce a hydrophobic composite with high bio-based content. AESO is synthesized from soybean oil (renewable resource abundantly available) via epoxidation and acryloilation. It contains three highly reactive functionalities, double (C=C) bonds, –OH groups, and epoxy rings. The C=C bond in AESO is capable of self-polymerizing and copolymerizing with other components via a freeradical initiation, forming a three-dimensional network. However, it has a low crosslinking density and thus inferior mechanical strength due to the existence of long aliphatic chains and low degree of unsaturation in AESO molecules. Also, it has high viscosity at room temperature that restricts its processability (Liu et al. , 2018). To reduce these limitations, a mixture was prepared by adding different reactive monomers to AESO at room temperature. This mixture was composed of acrylated epoxidized soybean oil (50% m/m); lauryl methacrylate (40% m/m)-a fatty acid‑based reactive diluent, potentially bio-based, which reduces the viscosity of the mixture (Cousinet et al. , 2015); 1,6-hexanodiol diacrylate (5% m/m); and tri(propylene glycol m/m) diacrylate (5% m/m)-bifunctional monomers which can enhance the crosslinking (Wei et al. , 2019).
Chapter 5 – Development of BC/emulsified AESO composites 69 5.3.3. Determination of the required hydrophilic–lipophilic balance (HLB) and AESO emulsion stability evaluation The Hydrophilic–Lipophilic Balance (HLB) values are generally considered vital for the stabilization of surfactant-based emulsions. Tritons and Spans are a range of non-ionic surfactants stable in mild alkalis, acids and electrolytes and have no reaction with ionic ingredients or actives. To prepare stable AESO emulsions, the effect of HLB was first studied by preparing different combinations of two non-ionic surfactants (Triton X-100 and Span 80) and a co-surfactant (Butanol) in a ratio of 2:1, as presented in Table 19. The HLB values of the mixed surfactants were calculated by Equation (4) (ICI Americas Inc., 1980): 𝐻𝐿𝐵𝑚𝑖𝑥 = (𝐻𝐿𝐵𝐴𝑋𝐴)+ (𝐻𝐿𝐵𝐵𝑋𝐵)+ (𝐻𝐿𝐵𝐶𝑋𝐶) , (4) where HLBmix , HLBA , HLBB , and HLBC are the HLB values of the mixture, Triton X-100, Span 80, and Butanol, respectively, and XA, XB and XC are the weight percentages of every surfactant in the mixture. HLB values from 5.20 (more lipophilic or oil soluble) up to 11.33 (more hydrophilic or water soluble) were obtained. The oil-in-water (O/W) emulsions were prepared with a mass ratio of 20:2:78 (AESO mixture/surfactant combination/water), as follows: 2 g of the surfactant combination (Table 19) were added to 20 g of the AESO mixture, followed by the addition of 78 g of deionized water. The mixture was emulsified using a homogenizer (Unidrive X 1000 D, CAT, Staufen, Germany) at a speed of 30,000 rpm, for 1, 5 and 10 min. This process was carried out in an ice bath to avoid temperature rise during emulsification. After this, the emulsions were stored in test tubes at room temperature to investigate their stability over time (up to 10 days) under conditions of varied HLB and stirring time. The stability was evaluated by visually recording signs of phase separation and creaming; the droplet morphology of the emulsions was investigated by optical microscopy using a Leica DM750 M microscope (Leica Microsystems, Wetzlar, Germany) with a Leica MC 170HD camera, using a 10× eyepiece lens and 100× objective lens.
Chapter 5 – Development of BC/emulsified AESO composites 70 Table 19. Combinations of surfactants used to study the effect of HLB on the AESO emulsion stability. Surfactant Combination Triton X-100 (%) (HLB = 13.5) 1 Span 80 (%) (HLB = 4.3) 1 Butanol (%) (HLB = 7.0) (ICI Americas Inc., 1980) HLBmix A 0.00 66.67 33.33 5.20 B 19.57 47.10 33.33 7.00 C 41.31 25.36 33.33 9.00 D 66.67 0.00 33.33 11.33 1 Values taken from the technical specification sheets 5.3.4. Exhaustion of BC membranes with emulsified AESO To test the incorporation of AESO in BC membranes, an emulsion was prepared by adding the initiator cumene hydroperoxide (CHP) (3% m/m) and the catalyst cobalt naphthenate (CONP) (0.8% m/m) to the AESO mixture. This initiator permits the polymerization of AESO at low temperatures (Dweib et al. , 2006), which prevents the aggregation or coalescence of the emulsified AESO particles. An emulsion with HLB of 11.3 (Table 19-D), which provided the best results obtained in the storage stability studies, was prepared using the same procedure described in section 5.3.3. BC membranes (with about 3.0 cm in thickness, with a size of 12.0 × 2.5 cm and weighting 90 g) were each treated by exhaustion with 100 g of emulsified AESO mixture for 9 days at 40 °C (Sample 1) followed by a 3 h curing step at 90 °C (Sample 2), to accelerate the cross-link of the emulsified AESO mixture. The composites were then dried at 40 °C in an oven (WTC series, Binder GmbH, Tuttlingen, Germany) for 5 days. To avoid shrinkage of the samples during drying, the composites were attached to a zincplated wire support. Regarding the exhaustion process, it was carried out in an Ibelus machine (IL-720, Labelus, Braga, Portugal) equipped with an infrared heating system, using stainless-steel cups with a capacity of approximately 220 cm3, with a rotation of 50 rpm, 40 cycles, and a temperature gradient of 2 °C·min−1. Samples were collected after the exhaustion process and before drying, for analysis by scanning electron cryomicroscopy (described below). 5.3.5. Production of composites with different polymers Several composites were also produced by adding other polymers to the pre-emulsified AESO mixture. These were PEG 400, Persoftal MS Conc.01 (PDMS-based softener (S)) and Baygard EFN (perfluoroarbonbased hydrophobizer (H)). Softeners (Persoftal) and hydrophobizers (Baygard) used in the textile industry
Chapter 5 – Development of BC/emulsified AESO composites 71 are usually liquid dispersions or emulsions that, in addition to active agents (polysiloxanes or fluorocarbons), contain emulsifiers (e.g. ethoxylated fatty alcohols), dispersants, defoamers. Details on the characteristics of Persoftal and Baygard are presented in Table 13 (section 3.3.1). PEG is a polymer with functionalities such as steric stabilization, which can be used to prevent particle agglomeration (Lima, Souza and Rosa, 2018); it is a nonionic surfactant able to form long chain structures in aqueous solution; it is also a plasticizer agent with the ability to increase molecular spacing, thus offering flexibility (Khalaf et al. , 2019). To produce the composites, BC membranes (with about 3.0 cm in thickness, with a size of 12.0 × 13.0 cm and weighting 450 g) were first squeezed to a final wet mass of 100 g. Then the compressed membranes were each treated by exhaustion with 100 g of an aqueous mixture as shown in Table 20, adding water to complete the 100 g. Table 20. Proportions of the polymers in the aqueous mixture used in the production of BC composites. Sample AESO Emulsion (g) PEG 400 (g) Persoftal MS (g) Baygard EFN (g) BC/AESO 75 - - - BC/AESO/PEG 75 4.5 - - BC/AESO/S 75 - 18 - BC/AESO/PEG/S 75 4.5 18 - BC/AESO/H 75 - - 18 BC/AESO/PEG/H 75 4.5 - 18 BC/AESO/PEG/S/H 75 4.5 9 9 For the preparation of these mixtures, the AESO mixture emulsion was first prepared as described on sections 5.3.3 and 5.3.4. Then PEG, Persoftal or Baygard were added and the mixture was stirred at 500 rpm for 1 min. The exhaustion treatment lasted for 5 days at 30 °C, in the same equipment above described, after which the samples were oven dried for 5 days at 40 °C, followed by a curing step for 3 h at 90 °C. As before, to avoid shrinkage of the samples during drying and curing, the composites were attached to a zinc-plated wire support. The polymer content in the final composites was calculated through the Equation (5):
Chapter 5 – Development of BC/emulsified AESO composites 78 BC impregnated with AESO mixture, both the added softener (S, Persoftal) and hydrophobizer (H, Baygard) presented lower impregnation. However, the opposite effect is observed adding PEG to either S, H or both mixtures, suggesting that PEG promoted a higher BC impregnation content. In the case of the mixtures of AESO, S and/or H, it is not possible to determine whether these were incorporated into BC in the same proportions as that of the emulsified AESO. Table 21. Thickness, mass per unit area and polymer content of the composites. Sample Thickness (mm) Mass Per Unit Area (g·m−2) Polymers content (%) BC 0.48 238.0 - BC/AESO 0.78 686.4 65.3 BC/AESO/PEG 0.55 576.0 58.7 BC/AESO/S 0.51 552.0 56.9 BC/AESO/PEG/S 0.79 921.6 74.2 BC/AESO/H 0.48 478.4 50.3 BC/AESO/PEG/H 0.72 886.4 73.1 BC/AESO/PEG/S/H 0.95 1032.5 76.9 5.4.3. Fourier transform infrared (FT-IR) Fourier transform infrared (FT-IR) spectroscopy was used to characterize the functional groups on the dried BC and BC composites’ surfaces (Figure 18). BC spectrum exhibited the characteristic cellulose vibration peaks, namely, –OH stretching peak at 3344 cm−1, C–H stretching at 2919 cm−1, –OH bending at 1650 cm−1, –CH2– bending at 1426 cm−1, C–O–C deformation modes and stretching vibrations at 1159–1107 cm−1, C–O–C and C–OH stretching vibration of the sugar ring at 1054–1029 cm−1, and C– OH out-of-plane bending mode at 665 cm−1 (Alonso et al. , 2018; He et al. , 2018; Sun et al. , 2018). The spectrum of the BC/AESO composite showed a peak at 3343 cm−1 corresponding to the stretching vibrations of –OH groups. The peaks at 2922–2855 cm−1 and at 1457–1406 cm−1 are attributed to the asymmetric stretching vibrations and deformation of C–H in the –CH2– and –CH3 bonds, respectively, assigned to the inherent aliphatic sequences of AESO. Another significant peak at 1721 cm−1 is attributed to the stretching vibration of C=O in esters and the one at 1637 cm−1 is ascribed to the double-bond signals of acrylate functionalities (–CH=CH2). The peaks at 1295 cm−1 and 1163–1053 cm−1 correspond to C–O groups and C–O–C stretching vibration of ester, respectively. Finally, the peak at 811 cm−1
Chapter 5 – Development of BC/emulsified AESO composites 79 corresponds to the bending vibration of =C–H, the double bonds on AESO characteristic of the epoxide group (Lu et al. , 2014; W. Liu et al. , 2017; Mandal and Maji, 2017). In the BC/AESO/PEG composite, the increase of some absorption bands can be attributed to PEG400, although they overlap with signals from cellulose and AESO mixture. These bands are located at 3345 cm−1 (–OH stretching), 2918–2854 cm−1 (CH2 stretching), 1644 cm−1 (–OH bending), 1456 cm−1 (asymmetric CH2 deformation), 1351 cm−1 (CH2 wagging), 1095–1029 cm−1 (CH2 symmetric deformation, C–O–C and C–OH stretching), 950 cm−1 (CH2 rocking), and 664 cm−1 (C–OH out-of-plane bending) (Araki and Mishima, 2015; Lima, Souza and Rosa, 2018). In the composite BC/AESO/S, the appearance of new peaks was observed, namely, at 1258 cm−1 (CH vibration in Si–CH3) and at 791 cm−1 (NH2 and Si–CH3), confirming the incorporation of modified aminoPDMS into the BC composite (Mohd et al. , 2016; Wu et al. , 2018; Zhang et al. , 2018). When PEG 400 was used in the polymer mixture, it was also observed at the peak at 1575 cm−1 that is attributed to the vibration modes of NH2 groups (Zargar, Nourmohammadi and Amosbediny, 2015). The vibration bands of Si–O–C and Si–O–Si bridges at around 1165–1011 cm−1 are difficult to analyze as they overlap with the C–O–C vibrations from BC and PEG (Saini et al. , 2016; Shao et al. , 2017). In the composites with perfluorcarbon (for BC/AESO/PEG/H), it was possible to identify the bands associated with CF2 groups (asymmetric and symmetric CF2 stretching at 1234 and 1141 cm−1 respectively and ‘amorphous’ CF2 deformations at 702 cm−1) (Mukherjee et al. , 2013). While in the composite BC/AESO/PEG/S/H, perfluorocarbon peaks are difficult to identify as they overlap with the characteristic peaks of the PDMS-based polymer.
Chapter 5 – Development of BC/emulsified AESO composites 80 Figure 18. FT-IR spectra of BC and the composites. 5.4.4. Surface wettability and surface free energy The BC composites are designed for leather (textile and footwear) applications; therefore, it is important to determine their surface hydrophobicity. The wetting properties of the BC and BC-based composites were investigated by measuring the water contact angles (WCAs). The obtained values are shown in Figure 19 and Figure 20. BC has a highly hydrophilic surface, bearing the lowest water droplet angle (63.1°), which increased for the BC composites to values between 79.0° and 138.0°, indicating a significant increase in hydrophobicity. Values of 95.8° and 79.0° were observed for BC/AESO and BC/AESO/PEG, respectively. AESO contains hydrophobic long-chain non-polar fatty acid chains (Li et al. , 2018) and consequently improves the water resistance of the composite. Despite being more hydrophobic, the WCAs over time decreased quickly in these composites, as compared to BC. This can be explained by the closed packed structure of the dried BC that limits the water diffusion through the tight space between the nanofibers, due to the strong and high number of cellulose–cellulose hydrogen bonds (Sun et al. , 2018). 6501 0501 4501 8502 2502 6503 0503 4503 850 Transmitance (u.a.) Wavenumber (cm−1) BC/AESO BC/AESO/PEG BC/AESO/S BC/AESO/H BC/AESO/PEG/S BC/AESO/PEG/H BC/AESO/PEG/S/H 2916 3345 2852 1325 1258 1463 1648 1551 1724 1011 867 794 3312 697 1057 949 810 702 1350 1234 1466 1551 1651 1728 2854 2916 3348 811 1053 1105 1163 1295 1406 1457 1637 1721 2855 2922 3343 866 1011 791 1258 666 1464 1543 2854 2959 1576 1644 1724 3348 2918 664 1295 810 1029 1351 1456 1644 1723 2918 841 1412 1118 1196 1034 2955 1412 1165 2854 949 1095 BC 3344 2919 1650 1054 1159 1426 1107 665 1029 1141
Chapter 5 – Development of BC/emulsified AESO composites 81 As expected, the incorporation of PDMS (S) and perfluorocarbon-based (H) polymers into BC also significantly increased the WCAs. Both polymers have very low surface tension, 19.5–23.6 mN·m−1 (X. Xu et al. , 2016; Tian et al. , 2018) and 6–18 mN·m−1 (Milionis, Bayer and Loth, 2016), respectively, thus decreasing the free energy of the system and reducing the surface wettability. However, in the samples with PEG, this increase was not as substantial, since PEG can interact with the BC membrane by hydrogen bonds. As stated by Kondo et al. (Kondo and Sawatari, 1994), the ether oxygen in the poly(ethylene oxide) skeleton forms hydrogen bonds with the primary OH group at the C6 position of the anhydroglucose unit. Promising results were observed with all H-composites: higher contact angles (Figure 20) and very low absorption rate over time (Figure 19). The increase in hydrophobicity resulted from a decrease in the polar component of the surface tension and consequently in the total surface free energy of the composite, as shown in Figure 20. An exception to this trend was observed for BC/AESO/PEG, where an increase in the surface free energy was recorded. Among the different polymers tested, AESO was the one that offered less hydrophobicity, and the incorporation of the PEG, being hydrophilic as observed above, increased the value of the polar component. Figure 19. Water contact angle over time. 0 30 60 90 120 150 020 40 60 80 100 120 140 160 180 Contact angle (°) Time (seconds) BC BC/AESO BC/AESO/PEG BC/AESO/S BC/AESO/PEG/S BC/AESO/H BC/AESO/PEG/H BC/AESO/PEG/S/H
Chapter 5 – Development of BC/emulsified AESO composites 82 Figure 20. Static water contact angle and surface free energy. 5.4.5. Thermal properties The thermal properties were evaluated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC and TGA curves of BC and its composites obtained under nitrogen atmosphere are depicted in Figure 21a,b, respectively, and the corresponding relevant data are summarized in Table 22. The DSC curve of BC reveals an endothermal degradation peak (Tm) at 362.2 °C, which is attributed to partial pyrolysis with the fragmentation of carbonyl and carboxylic bonds from anhydrous glucose units (Barud et al. , 2011). BC also shows a narrow weight loss at 351.0 °C (Tdmax), indicating fast degradation, involving dehydration, depolymerization of the main polymer network and the decomposition of glucosyl units followed by the formation of a charred residue (Frone et al. , 2018; Hu et al. , 2018). In the case of the composites, an additional endothermic transition below 100 °C is observed in the DSC curves, it corresponds to the first step of weight loss in the temperature range of 30–150 °C observed in Figure 21b, which is ascribed to the loss of absorbed water. From Table 22, it is possible to observe that the composites with PEG 400 lost 5% of their mass at lower temperatures; this occurs because lowmolecular polyethylene glycol contributes to higher hygroscopicity, the water being released by evaporation. These samples also present less charred residue, when compared with the composites without PEG. For most of the composites, a second event, in the range of 100–250 °C, is observed before the main degradation. This degradation stage can be considered the evaporation and 63.1 95.8 79.0 120.7 120.7 133.6 127.7 137.9 0 40 80 120 160 0 15 30 45 60 Water contact angle (°) Surface free energy (mJ·m−2) Total surface free energy Dispersive Polar Water contact angle (b)
Chapter 5 – Development of BC/emulsified AESO composites 83 decomposition of unreacted monomers, catalysts, or other low molecular weight components in the composites (Liu et al. , 2015; Liu, Madbouly and Kessler, 2015; Zhang et al. , 2015; F. Liu et al. , 2017). All DSC curves of the composites display exothermic transitions up to 200 °C, which we hypothesize to correspond to the polymerization of unreacted AESO (Liu, Xie and Qiu, 2017). A redox initiator system (the initiator cumene hydroperoxide (CHP) and the promoter cobalt naphthenate (CONP)) was used to polymerize AESO during the exhaustion process. This was performed at a relatively low temperature (30 °C), as described by other authors (Dweib et al. , 2006), attempting to avoid coalescence of the emulsified AESO (which is favored at a higher temperature due to the reduction of viscosity). However, as stated by Dweib et al. (2006), oxygen and water inhibit the free-radical polymerization reaction and the complete curing of the resins. In this work, emulsified AESO was cured, probably not completely, in aqueous media. Thus, the exothermic peak in DSC curves may be associated with the free-radical polymerization. Indeed, this peak does not appear in the AESO mixture curve tested without the addition of a catalyst on Figure 21a. The increase in temperature promoted the decomposition of the initiator CHP, generating more free radicals to complete the polymerization. Further, the degradation of the composite network structure constitutes the second endothermic transition at higher temperatures. The beginning of the structural disruption is defined as the temperature where 10 wt% of the mass is lost. It was observed that T10wt% for BC (326.4 °C) was higher than T10wt% for all composites. Therefore, it can be inferred that native BC is more thermally stable than the polymeric composites. The composites show less pronounced peaks with the main mass loss step, corresponding to the higher percentage of mass loss, observed in a broader temperature range. The Tdmax decreases in the order BC > BC/AESO > BC/AESO/PEG > BC/AESO/S > BC/AESO/PEG/S > BC/AESO/PEG/S/H > BC/AESO/H > BC/AESO/PEG/H and these results are in accordance with the DSC data. Although the composites are less stable thermally, they are stable up to 200 °C, so they can be applied in common leather applications.
Chapter 5 – Development of BC/emulsified AESO composites 84 Figure 21. (a) DSC thermograms and (b) TGA curves of weight percentage of dried BC and BC composites. Table 22. Thermal degradation data obtained from DSC, TGA and DTG curves of dried BC and BC composites. Sample Tc (°C) a Tm (°C) b T5 wt% a (°C) c T10 wt% b (°C) d Tdmax d (°C) e BC - 362.2 136.1 326.4 351.0 BC/AESO 127.3 365.0 221.9 305.0 364.4 BC/AESO/PEG 153.2 387.2 136.8 236.8 372.7 BC/AESO/S 158.1 387.6 161.9 242.9 375.9 BC/AESO/PEG/S 157.3 389.9 132.5 196.9 374.3 BC/AESO/H 161.8 350.2 161.4 232.9 353.1 BC/AESO/PEG/H 151.9 365.5 109.5 217.4 361.9 BC/AESO/PEG/S/H 150.1 388.4 192.4 263.8 333.8/400.8 a Temperature of the curing exotherm maximum; b Temperature of the degradation endothermal maximum; c Temperature at 5% mass loss; d Temperature at 10% mass loss; and, e Temperature(s) at the maximum mass loss rate. -8 -5 -2 1 4 25 125 225 325 425 Heat flow (mW) >>> EXO Temperature (°C) BC AESO mixture BC/AESO BC/AESO/PEG BC/AESO/S BC/AESO/PEG/S BC/AESO/H BC/AESO/PEG/H BC/AESO/PEG/S/H (a) 0 20 40 60 80 100 0100 200 300 400 500 600 Weight (wt%) Temperature (°C) BC BC/AESO BC/AESO/PEG BC/AESO/S BC/AESO/PEG/S BC/AESO/H BC/AESO/PEG/H BC/AESO/PEG/S/H (b)
Chapter 5 – Development of BC/emulsified AESO composites 85 5.4.6. Mechanical properties The average values and standard deviation of the tensile strength and elongation at break of the BC and BC-based composites are reported in Table 23, and the stress–strain curves are given in Figure 22. As deduced from Figure 22, neat BC displayed a rigid and brittle behavior, because of the extensive interactions between the polymer molecules that result in high tensile strength but low elongation at break. The incorporation of the plasticizers into polymers disrupts the intermolecular attractive forces between the main polymer chains and consequently increases the free volume and chain mobility, leading to an increase in extensibility (Boon, Lim and Gong, 2018; Sun et al. , 2018; Salarbashi, Bazeli and Tafaghodi, 2019). Thus, when compared to the neat BC membrane, the incorporation of emulsified polymer mixtures leads to a reduction in the values of the tensile strength and an increase in the elongation at break. As observed by SEM (Figure 17), the polymers appeared to have completely covered the surface of the BC nanofibers, resulting in an increase in the composites’ thickness (Table 21). As observed by DSC, AESO was not completely polymerized, thus it may have not fully acted as a reinforcing agent but also as a plasticizer, allowing higher mobility between the different layers of the BC membrane. The addition of either S or H, to BC/AESO, improved the mechanical and elongation properties of the composites, as compared to BC/AESO. However, only for this composite (BC/AESO) the addition of PEG allowed increasing the mechanical properties. In general, it was observed that the addition of different polymers leads to a decrease in tensile strength and an increase in elongation at break. The incorporation of PEG resulted in a consistent and significant increase in the elongation at break values due to its plasticizing effect. Overall, taking as reference the technical report ISO/TR20879 (ISO, 2007), with respect to the mechanical properties, most of the composites are suitable to be used in footwear. Regarding tensile strength values, BC/AESO/PEG/S, BC/AESO/PEG/H, and BC/AESO/PEG/S/H samples (more polymer content as shown in Table 21) were below the reference value (casual footwear: >10 N·mm−1) (MPa × Thickness), but in the case of the elongation at break, all samples presented values within the required reference values.
Chapter 5 – Development of BC/emulsified AESO composites 86 Table 23. Tensile strength and elongation at break of dried BC and BC composites. Sample Tensile strength (MPa) Elongation at break (%) BC 37.5 ± 0.8 3.6 ± 0.6 BC/AESO 17.3 ± 0.7 9.5 ± 1.0 BC/AESO/PEG 24.6 ± 1.7 13.9 ± 0.8 BC/AESO/S 22.6 ± 3.3 8.4 ± 0.1 BC/AESO/PEG/S 6.3 ± 1.0 9.4 ± 2.3 BC/AESO/H 35.9 ± 3.0 9.5 ± 0.2 BC/AESO/PEG/H 11.8 ± 1.0 12.9 ± 2.0 BC/AESO/PEG/S/H 6.9 ± 0.2 10.0 ± 0.5 Figure 22. Stress strain curves of dried BC and BC composites. 5.5. Conclusion This work provided a straightforward method to prepare BC composites with high potential for applications as a replacement for leather. We have successfully prepared composites based on BC, emulsified AESO resin, PEG, and PDMSand perfluorocarbon-based polymers through a simple strategy to enhance the flexibility and hydrophobicity of the BC. Based on SEM observations and FT-IR analysis, all the tested polymers penetrated well and uniformly into the BC matrix. The obtained composites showed hydrophobicity with the highest values of WCAs obtained for the composites with the perfluorocarbon-based product. Regarding the thermal and mechanical 0 10 20 30 40 0 3 6 9 12 15 Tensile strength (MPa) Elongation (%) BC BC/AESO BC/AESO/PEG BC/AESO/S BC/AESO/PEG/S BC/AESO/H BC/AESO/PEG/H BC/AESO/PEG/S/H
Chapter 5 – Development of BC/emulsified AESO composites 87 properties, it was found that the composites presented lower thermal stability and tensile strength, although they are stable up to 200 °C and most of the composites can be applied in uppers for shoes. Further optimization of the process may improve its performance through improved control of the polymerization reaction. Hence, this work opens new perspectives for potential applications of BC in the footwear industry.
Chapter 6 – Development of BC-based composites polymerized with H2O2/AA, finishing and dyeing 94 6.4. Results and discussion 6.4.1. Properties of the composites The obtained composites were characterized regarding their wettability, water vapor permeability (WVP), mechanical and thermal properties, Table 26, Figure 23 and Figure 24. As observed by the considerable increase in thickness (Table 26), the AESO emulsion mixture (Table 24) penetrated well into the BC membranes. The water contact angles values further confirmed the impregnation of the BC by changing its surface wettability (WCA > 90°), which is slightly higher in the sample with the AESO polymerized after the exhaustion process (Composite B). As observed in Chapter 5, the incorporation of PDMS-based polymer into BC significantly increased the WCA of the composites. The low surface tension of PDMS, which is 19.5–23.6 mN·m−1 (X. Xu et al. , 2016; Tian et al. , 2018), contributes to the decrease in the free energy and the surface wettability of the composite. Furthermore, AESO resin contains hydrophobic long-chain non-polar fatty acid chains (Li et al. , 2018), which improve the hydrophobicity of the composites. Regarding the water vapor permeability, although the BC porosity was not completely obstructed by the incorporation of the polymer’s mixture, the WVP values were much lower than those of pristine BC, which can be also explained by the higher thickness of the composites and their hydrophobic character. As shown in the previous chapters, the increased thickness and water resistance of the composites affected the adsorption process of the water vapor permeation mechanism. Concerning the mechanical properties, as compared to BC, the tensile strength of the composites was lower but the elongation was much higher. These results can be explained by the extensive surface coating of the surface hydroxyl groups of the cellulose nanofibers which prevents their contribution to the mechanical strength through hydrogen bonding (Soykeabkaew et al. , 2009; Gea et al. , 2010; Asgher, Ahmad and Iqbal, 2017). Hence, the mechanical strength and elongation of the composites become dependent on the intermolecular bonding of the matrix polymers. The added polymers also had a plasticizing effect, which increased the free volume and allowed greater mobility between the different layers of the BC membrane (Boon, Lim and Gong, 2018; Sun et al. , 2018; Salarbashi, Bazeli and Tafaghodi, 2019). Composite B showed lower tensile strength value owing to the lower degree of polymerization of the crosslinked AESO, as will be discussed below.
Chapter 6 – Development of BC-based composites polymerized with H2O2/AA, finishing and dyeing 95 Table 26. Properties of the BC and BC composites. Thermogravimetric analysis (TGA) was used to evaluate the thermal properties and kinetics of degradation of the composites. The TGA and the derivative thermograms (DTG) are shown in Figure 23. DTG curve of BC shows a single and narrow weight loss at 351.0 °C, indicating a fast degradation, involving dehydration, depolymerization of the main polymer network and the decomposition of glucosyl units followed by the formation of a charred residue (Frone et al. , 2018; Hu et al. , 2018). In the case of the composites, each of the samples presented two distinct peaks. Composite B (post-polymerization) shows one first event at 182.4 °C before the main degradation. This degradation stage can be considered the evaporation and decomposition of unreacted monomers, catalysts, or other low molecular weight components in the composites (Liu et al. , 2015; Liu, Madbouly and Kessler, 2015; Zhang et al. , 2015; F. Liu et al. , 2017). On the other hand, Composite A (pre-polymerization) had the first degradation peak at 328.3 °C and, hence, it can be inferred that the pre-polymerization using the redox initiator system hydrogen peroxide/L-ascorbic acid was more effective when compared to the post-polymerization. This can explain the lower WVP and tensile strength, higher contact angle and the higher elongation values of Composite B. The main mass loss step of both composites corresponding to the highest percentage of mass loss occurred at higher temperatures for the composites as compared to BC, respectively, at 392.6 °C and 373.1 °C for Composites A and B. This can be attributed to the decomposition of PDMS-based polymer and crosslinked AESO. The temperature corresponding to the maximum rate of weight-loss of the polymers was around 420 °C (Radhakrishnan, 2005; Sousa et al. , 2017). Sample Thickness (mm) WCA (°) WVP (g·m−2·24 h−1) Tensile strength (MPa) Elongation (%) BC 0.48 ± 0.01 63.1 ± 4.7 289.6 37.5 ± 0.8 3.6 ± 0.6 Composite A (pre-polymerization) 1.27 ± 0.01 93.1 ± 5.7 65.1 ± 1.3 12.1 ± 1.8 15.5 ± 0.9 Composite B (post-polymerization) 1.22 ± 0.01 103.6 ± 3.2 28.8 ± 2.7 8.3 ± 0.4 19.1 ± 4.5
Chapter 6 – Development of BC-based composites polymerized with H2O2/AA, finishing and dyeing 96 Figure 23. TGA curves (solid lines) and respective derivative (dashed lines) of BC and BC composites. The storage modulus (E’) obtained by dynamic mechanical analysis (DMA) of pure BC and the composites over a temperature range of 25 °C to 250 °C at a frequency of 1 Hz is presented in Figure 24. The obtained data show that BC has high stiffness with a storage modulus at room temperature of 6.5 GPa due to the strong hydrogen bonds between the nanofibers. However, a considerably lower storage modulus was observed for the BC composites, which can be ascribed to the plasticizing effect of the impregnated polymers resulting in the segmental mobilization of the nanocellulose chains. Among the composites, Composite A showed a higher storage modulus for temperatures up to approximately 100 °C. These results are in good agreement with the tensile strength measurements, which were plausibly associated with a higher crosslinking density. In addition, it was also possible to observe that the storage modulus of Composite B decreased when the temperature rose to 55 °C and then increased when it rose to 130 °C. This could be due to the loss of unreacted material, as was observed in the TGA results, which consequently gave rise to densification of the composite structure during heating, allowing an improved stress transfer behavior at higher temperatures. 0 0.5 1 1.5 2 2.5 0 20 40 60 80 100 0100 200 300 400 500 600 DTG (%/ºC) Weight (%) Temperature (ºC) BC Composite A (pre-polymerization) Composite B (post-polymerization)
Chapter 6 – Development of BC-based composites polymerized with H2O2/AA, finishing and dyeing 97 Figure 24. Evolution of the storage modulus (E’) versus temperature at 1 Hz for BC (inserted graph) and BC composites as obtained by dynamic mechanical analysis Comparing the results of these composites, by using the redox initiator system hydrogen peroxide and Lascorbic acid with the ones from Chapter 5 a substantial improvement in the elongation at break (prepolymerization and post-polymerization) and in the tensile strength (pre-polymerization) was achieved. Overall, the polymerization of the AESO emulsion using biodegradable catalysts was validated and since the polymerization occurred before the exhaustion process, this method was more effective in the preparation of the composites. 6.4.2. Antimicrobial activity The antibacterial activity of the BC composites finished (surface-functionalized) with different concentrations and time of exhaustion of the biocide benzalkonium chloride (BAC), against S. aureus and E. coli , was determined using the zone of inhibition method. S. aureus and E. coli are among the most prevalent species of gram-positive and gram-negative bacteria, respectively. As shown in Figure 25, all samples with the biocide compound produced a zone of inhibition (halo) against the S. aureus (Grampositive), and this area increased with concentration and with the time of treatment. No inhibition was observed against the E. coli , possibly due to the poor antimicrobial capacity of the benzalkonium chloride (cationic) against gram-negative bacteria (Wei, Yang and Hong, 2011). 0 0.05 0.1 0.15 0.2 0.25 0.3 25 50 75 100 125 150 175 200 225 250 E' (GPa) Temperature (°C) Composite A (pre-polymerization) Composite B (post-polymerization) BC
Chapter 6 – Development of BC-based composites polymerized with H2O2/AA, finishing and dyeing 98 Control 1 BAC (2%, 30 min) 2 BAC (2%, 60 min) 3 BAC (4%, 60 min) E. coli S. aureus Figure 25. Antibacterial activity of the BC composites surface-functionalized with benzalkonium chloride-based product against Escherichia coli and Staphylococcus aureus . 6.4.3. Dyeing Figure 26 shows some photos of the dyed composites. All samples showed intense colors, were very flexible and hydrophobic (inserted photo in Figure 26e as an example). For samples dyed during the exhaustion with the AESO mixture, Figure 26a-f, the dye diffused well into the membranes, resulting in more uniform colors. However, in samples dyed after the production of the composites, Figure 26g-h, the dye remained only at the outer layers (inserted photo in Figure 26g) and the color was less uniform. It was also possible to observe that by increasing the temperature during dyeing with the dispersed dye, Figure 26i, more intense colors were obtained and despite the greater shrinkage of the sample, this change contributed to obtaining a material with a texture more similar to that of leather. From the above, incorporating the dye simultaneously with the AESO mixture is a more efficient approach towards dyeing BC composites. These results also allowed to present a simple and potentially low-cost strategy for this process, albeit it will be necessary to carry out color washing and rubbing fastness tests, as well as to optimize the process conditions, taking into account the variables of pH, bath ratio, temperature, dye concentration, auxiliary products and the duration of the process.
Chapter 6 – Development of BC-based composites polymerized with H2O2/AA, finishing and dyeing 99 Figure 26. Photos of the dyed BC composites. Letters (a–i) correspond to the experimental conditions described in Section 6.3.3.2. Simultaneous dyeing and production of the BC-based composites (a–f) and dyeing of dry composites (g–i). 6.5. Conclusion After carrying out this work, the possibility of producing BC composites by incorporating, through the exhaustion process, products based on AESO, PDMS, and PEG 400, using biodegradable catalysts was validated. The polymerization of the AESO emulsion before the exhaustion process proved to be more effective in terms of WVP, tensile strength and thermal stability. However more work is needed to optimize the process. Composites finished with biocides showed antimicrobial activity against S. aureus and incorporating the dye simultaneously with the AESO mixture was the most efficient approach towards composites with intense colors. (a) (b) (c) (d) (e) (f) (g) (h) (i) 60 °C 80 °C 100 °C 120 °C
100 Chapter 7 Conclusions and suggestions for future work 7.1. Main conclusion This project aimed at using bacterial cellulose (BC) as a structuring material, for the development of a new leather analogue from alternative biological products, specifically with modified vegetable oils and other hydrophobic polymers. In this concept, BC, a highly porous nanofibrillar natural material, was submitted to an exhaustion process, allowing the bulk impregnation of hydrophobic polymers, namely commercial nano/microparticles, Persoftal MS Con.01 (polydimethylsiloxane (PDMS)-based) and Baygard EFN (perfluorocarbon (PFC)-based), and acrylated epoxidized soybean oil (AESO). In a first approach, BC-based nanocomposites were developed by impregnating BC membranes with PDMSor PFC-based products, each, at different concentrations, and with both polymers in a sequential process. Both hydrophobic products penetrated well in the BC membranes, adsorbing tightly onto the surface of the nanofibers, across the entire depth of the material, as observed by scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR). The incorporation of increasing amounts of PDMSor PFC-based products increased the thickness and the mass per unit area of the composites, while decreasing the water vapor permeability (WVP). After incorporation of the polymers, higher contact angles (CAs) were obtained, indicative of more hydrophobic surfaces, and the use of PFC-based product seems to provide more hydrophobicity. The mechanical properties of the composites improved with the incorporation of the polymers, although, as the concentration of the added products increased, the tensile strength and Young’s modulus decreased. It was also observed that samples with higher amounts of incorporated polymers, had higher elongation. Overall, the resulting composites were malleable, mechanically resistant, hydrophobic, and breathable. Then, aiming at increasing the bio-based content of the composite, BC membranes were impregnated with activated vegetable oils, AESO, in a mixture containing also the PDMS-based polymer and
Chapter 7 – Conclusions and suggestions for future work 101 polyethylene glycol (PEG) 400. FT-IR and SEM analyses provided evidence of the incorporation of these polymers into the BC membrane, resulting in its hydrophobic performance. The incorporation of the AESO resin in the PDMS/PEG mixture contributed to an increase in the values of tensile strength and a decrease in the elongation, while the addition of the plasticizer PEG 400 increased the elongation and decreased the tensile strength. Using a new approach, AESO resin was previously emulsified to allow better diffusion into the BC membranes and applied in mixtures containing also PEG 400, and PDMSand PFC-based products. All the tested polymer mixtures penetrated well and uniformly into the BC matrix, as shown on SEM observations and FT-IR analysis. The obtained composites were hydrophobic and the highest values of CAs were obtained for the composites with the PFC-based product (CAs of 128-138°). Regarding the thermal properties, it was found that the composites presented lower thermal stability than the BC, although they were stable up to 200 °C. From differential scanning calorimetry (DSC) analysis, it was observed that AESO resin was not fully cured. Further optimization of the polymerization may improve its performance. When compared to BC/AESO composite, the addition of either PDMSor PFC-based product, improved the mechanical and elongation properties of the composites and, in general, the incorporation of PEG resulted in a consistent and significant increase in the elongation at break values due to its plasticizing effect. Finally, it was demonstrated that AESO emulsion can be polymerized using the redox initiator system H2O2/AA. When the composites were developed with the mixture containing the previously polymerized AESO emulsion, greater WVP, tensile strength and thermal stability were obtained, while the composites polymerized after the exhaustion presented higher hydrophobicity and elongation. It was also shown that the composites finished with an antimicrobial agent, had antimicrobial action against S. aureus bacterium. Also, composites with intense colors were obtained by incorporating the dye simultaneously with the polymer’s mixture, resulting in a more uniform distribution of the color, as compared to post-dyed composites. Summing up, this work demonstrated new approaches to develop composites based on bacterial cellulose and hydrophobic polymers, including modified soybean oil, opening new perspectives for the potential applications of BC and thus offer a high value-added differentiation and sustainable consumer products, such as textiles and leather. The exhaustion process here used, is already available at large scale and represents a simple and cost-effective approach towards the production of these composites.
Chapter 7 – Conclusions and suggestions for future work 102 7.2. Suggestions for future work Based on the results obtained in this work, the following suggestions can be made for future work: - The results showed that BC composites with distinct performances can be designed by simply varying the polymers percentage contents. Optimization of the polymer’s mixture regarding the percentage of each component, may allow to improve the final properties of the composites, considering their applications in leather products. - There were technical difficulties in the polymerization process, which should have been done under controlled temperature and inert atmosphere conditions. Full optimization of the AESO polymerization may allow better results in terms of the composite’s final properties. - Test the composites freeze-drying. Although it is an expensive process, it may be possible to increase the water vapor permeability. - Optimization of the dyeing process, considering the variables of pH, bath ratio, temperature, dye concentration, auxiliary products, and the duration of the process. - Finishing of the composites by spray-coating and/or by imprint a pattern to make its appearance more appealing. - Evaluation of the properties of the composites considering the requirements for its application as an alternative to leather. - Determination of the biodegradability of the composites. - Study of the environmental impact (life cycle).
103 Chapter 8 References Abeer, M. M., Mohd, M. C. I. and Martin, C. (2014) “A review of bacterial cellulose-based drug delivery systems: their biochemistry, current approaches and future prospects,” Journal of Pharmacy and Pharmacology , 66, pp. 1047–1061. doi: 10.1111/jphp.12234. Akesson, D., Skrifvars, M. and Walkenström, P. (2009) “Preparation of thermoset composites from natural fibres and acrylate modified soybean oil resins,” Journal of Applied Polymer Science , 114, pp. 2502–2508. doi: 10.1002/app. Alonso, E., Faria, M., Faranak, M., Resnik, M., Ferreira, A. and Cordeiro, N. (2018) “Conductive bacterial cellulose-polyaniline blends: influence of the matrix and synthesis conditions,” Carbohydrate Polymers , 183, pp. 254–262. doi: 10.1016/j.carbpol.2017.12.025. Ananas-anam (2017) Introducing piñatex TM - ananas anam , Ananas-anam . Available at: http://www.ananas-anam.com/pinatex/ (Accessed: November 10, 2017). Andrade, F. K., Pertile, R. A. N., Dourado, F. and Gama, F. M. (2010) “Bacterial cellulose: properties, production and applications.,” in Lejeune, A. and Deprez, T. (eds.) Cellulose: Structure and Properties, Derivatives and Industrial Uses . New York: Nova Science Publishers, Inc, pp. 427–458. Araki, J. and Mishima, S. (2015) “Steric stabilization of ‘charge-free’ cellulose nanowhiskers by grafting of poly(ethylene glycol),” Molecules , 20, pp. 169–184. doi: 10.3390/molecules20010169. Araújo, I. M. S., Silva, R. R., Pacheco, G., Lustri, W. R., Tercjak, A., Gutierrez, J., Júnior, J. R. S., Azevedo, F. H. C., Figuêredo, G. S., Vega, M. L., Ribeiro, S. J. L. and Barud, H. S. (2018) “Hydrothermal synthesis of bacterial cellulose – copper oxide nanocomposites and evaluation of their antimicrobial activity,” Carbohydrate Polymers , 179, pp. 341–349. doi: 10.1016/j.carbpol.2017.09.081. Araújo, S., Silva, F. M. da and Gouveia, I. C. (2015) “The role of technology towards a new bacterialcellulose-based material for fashion design,” Journal of Industrial and Intelligent Information , 3(2), pp. 168–172. doi: 10.12720/jiii.3.2.168-172. Asgher, M., Ahmad, Z. and Iqbal, H. M. N. (2017) “Bacterial cellulose-assisted de-lignified wheat strawPVA based bio-composites with novel characteristics,” Carbohydrate Polymers , 161, pp. 244–252. doi: 10.1016/j.carbpol.2017.01.032. Barud, H. S., Souza, J. L., Santos, D. B., Crespi, M. S., Ribeiro, C. A., Messaddeq, Y. and Ribeiro, S. J. L. (2011) “Bacterial cellulose/poly (3-hydroxybutyrate) composite membranes,” Carbohydrate Polymers , 83, pp. 1279–1284. doi: 10.1016/j.carbpol.2010.09.049. Basil-Jones, M. M., Edmonds, R. L., Allsop, T. F., Cooper, S. M., Holmes, G., Norris, G. E., Cookson, D. J., Kirby, N. and Haverkamp, R. G. (2010) “Leather structure determination by small-angle X-ray
Chapter 8 – References 110 Kuraray (2018) ClarinoTM , Kuraray America . Available at: http://www.clarino-am.com/science.php (Accessed: March 16, 2018). Laurenti, R., Redwood, M., Puig, R. and Frostell, B. (2016) “Measuring the environmental footprint of leather processing technologies,” Journal of Industrial Ecology , 21(5), pp. 1180–1187. doi: 10.1111/jiec.12504. Leber, J. (2016) Real leather grown in a lab is moving closer to your closet , Fast Company . Available at: https://www.fastcompany.com/3061337/real-leather-grown-in-a-lab-is-moving-closer-to-you-closet (Accessed: October 19, 2017). Lee, K.-Y., Blaker, J. J. and Bismarck, A. (2009) “Surface functionalisation of bacterial cellulose as the route to produce green polylactide nanocomposites with improved properties,” Composites Science and Technology , 69(15–16), pp. 2724–2733. doi: 10.1016/j.compscitech.2009.08.016. Lee, K.-Y., Buldum, G., Mantalaris, A. and Bismarck, A. (2014) “More than meets the eye in bacterial cellulose: Biosynthesis, bioprocessing, and applications in advanced fiber composites,” Macromolecular Bioscience , 14, pp. 10–32. doi: 10.1002/mabi.201300298. Lee, K.-Y., Quero, F., Blaker, J. J., Hill, C. A. S., Eichhorn, S. J. and Bismarck, A. (2011) “Surface only modification of bacterial cellulose nanofibres with organic acids,” Cellulose , 18(3), pp. 595–605. doi: 10.1007/s10570-011-9525-z. Lee, K.-Y., Wong, L. L. C., Blaker, J. J., Hodgkinson, J. M. and Bismarck, A. (2011) “Bio-based macroporous polymer nanocomposites made by mechanical frothing of acrylated epoxidised soybean oil,” Green Chemistry , 13(11), pp. 3117–3123. doi: 10.1039/c1gc15655a. Lee, S. (2011) Grow your own clothes , TED Talk . Available at: https://www.ted.com/talks/suzanne_lee_grow_your_own_clothes/transcript (Accessed: November 2, 2016). Lee, T. S., Choi, H. Y., Choi, H. N., Lee, K.-Y., Kim, S.-H., Lee, S. G. and Yong, D. K. (2013) “Effect of surface treatment of ramie fiber on the interfacial adhesion of ramie/acetylated epoxidized soybean oil (AESO) green composite,” Journal of Adhesion Science and Technology , 27(12), pp. 1335–1347. doi: 10.1080/01694243.2012.697326. Lee, Y.-A., Li, R. and Nam, C. (2016) “Consumers’ acceptance of sustainable apparel products made of bacterial cellulose materials,” in International Textile and Apparel Association (ITAA) Annual Conference Proceedings . Vancouver, pp. 1–3. Available at: https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1488&context=itaa_proceedings. Lee, Y.-A., Xiang, C., Ghalachyan, A., Ramasubramanian, G., Li, R., Madbouly, S. and Farr, C. (2014) “Exploring optimal solutions for sustainable product development using renewable bacteria cellulose fiber and biopolymer composites,” in 2014 ITAA Proceedings #71 . Charlotte, pp. 8–9. Lee, Y. A. (2016) “Case study of renewable bacteria cellulose fiber and biopolymer composites in sustainable design practices,” in Muthu, S. S. and Gardetti, M. A. (eds.) Sustainable Fibres for Fashion Industry . Singapore: Springer. doi: 10.1007/978-981-10-0522-0. Lemal, D. M. (2004) “Perspective on Fluorocarbon Chemistry,” Journal of Organic Chemistry , 69(1), pp. 1–11. doi: 10.1021/jo0302556. Li, C., Xiao, H., Wang, X. and Zhao, T. (2018) “Development of green waterborne UV-curable vegetable oil-based urethane acrylate pigment prints adhesive: Preparation and application,” Journal of Cleaner Production , 180, pp. 272–279. doi: 10.1016/j.jclepro.2018.01.193.
Chapter 8 – References 111 Li, L., Zhou, Z., Yang, B., Ji, X., Huang, H., Zhong, G. and Xu, L. (2019) “Robust cellulose nanocomposite films based on covalently cross-linked network with effective resistance to water permeability,” Carbohydrate Polymers journal , 211, pp. 237–248. doi: 10.1016/j.carbpol.2019.01.084. Life Materials (2017) MuSkin – samples and small production amounts . Available at: https://lifematerials.eu/en/shop/muskin/ (Accessed: November 10, 2017). Lima, G. F. De, Souza, A. G. De and Rosa, D. S. (2018) “Effect of adsorption of polyethylene glycol (PEG), in aqueous media, to improve cellulose nanostructures stability,” Journal of Molecular Liquids , 268, pp. 415–424. doi: 10.1016/j.molliq.2018.07.080. Liu, C., Liu, Z., Tisserat, B. H., Wang, R., Schuman, T. P., Zhou, Y. and Hu, L. (2015) “Microwave-assisted maleation of tung oil for bio-based products with versatile applications,” Industrial Crops & Products , 71, pp. 185–196. doi: 10.1016/j.indcrop.2015.02.066. Liu, F., Miao, L., Wang, Y., Xue, X. and Yang, H. (2017) “Progress in organic coatings green fabrication of ultraviolet curable epoxy acrylate-silica hybrid coatings,” Progress in Organic Coatings , 109, pp. 38– 44. doi: 10.1016/j.porgcoat.2017.04.015. Liu, K., Madbouly, S. A. and Kessler, M. R. (2015) “Biorenewable thermosetting copolymer based on soybean oil and eugenol,” European Polymer Journal , 69, pp. 16–28. doi: 10.1016/j.eurpolymj.2015.05.021. Liu, W., Fei, M., Ban, Y., Jia, A. and Qiu, R. (2017) “Preparation and evaluation of green composites from microcrystalline cellulose and a soybean-oil derivative,” Polymers , 9(10), p. 541. doi: 10.3390/polym9100541. Liu, W., Fei, M. en, Ban, Y., Jia, A., Qiu, R. and Qiu, J. (2018) “Concurrent improvements in crosslinking degree and interfacial adhesion of hemp fibers reinforced acrylated epoxidized soybean oil composites,” Composites Science and Technology , 160, pp. 60–68. doi: 10.1016/j.compscitech.2018.03.019. Liu, W., Xie, T. and Qiu, R. (2017) “Biobased thermosets prepared from rigid isosorbide and flexible soybean oil derivatives,” ACS Sustainable Chemistry and Engineering , 5(1), pp. 774–783. doi: 10.1021/acssuschemeng.6b02117. Live kindly (2018) Fashion designer creates vegan leather softer than real cow hide , Live kindly . Available at: https://www.livekindly.co/vegan-lino-linoleum-leather-softer-than-cow-hide/ (Accessed: September 1, 2020). López, S. H. and Santiago, E. V. (2013) “Acrylated-epoxidized soybean oil-based polymers and their use in the generation of electrically conductive polymer composites,” in El-Shemy, H. A. (ed.) Soybean - BioActive Compounds . London: IntechOpen Limited, pp. 231–263. doi: 10.5772/52992. Lu, J. and Wool, R. P. (2004) “Development of new green SMC resins and nanocomposites from plant oils,” in 4th Anual SPE Automotive Composites Conference, Troy, MI, USA, 14-15 September 2004 . Lu, P., Xiao, H., Zhang, W. and Gong, G. (2014) “Reactive coating of soybean oil-based polymer on nanofibrillated cellulose film for water vapor barrier packaging,” Carbohydrate Polymers , 111, pp. 524– 529. doi: 10.1016/j.carbpol.2014.04.071. Ludwicka, K., Jedrzejczak-Krzepkowska, M., Kubiak, K., Kolodziejczyk, M., Pankiewicz, T. and Bielecki, S. (2016) “Medical and cosmetic applications of bacterial nanocellulose,” in Gama, M., Dourado, F., and Bielecki, S. (eds.) Bacterial Nanocellulose: From Biotechnology to Bio-Economy . Amsterdam: Elsevier B.V, p. 262. doi: http://dx.doi.org/10.1016/B978-0-444-63458-0.00007-X. Mandal, M. and Maji, T. K. (2017) “Comparative study on the properties of wood polymer composites
Chapter 8 – References 112 based on different modified soybean oils,” Journal of Wood Chemistry and Technology , 37(2), pp. 124– 135. doi: 10.1080/02773813.2016.1253099. Material District (2019) Leather-free handbag made of bacterial cellulose , Material District . Available at: https://materialdistrict.com/article/handbag-bacterial-cellulose/ (Accessed: August 25, 2020). Materials District (2019) Furniture made from apple leather , Materials District . Available at: https://materialdistrict.com/article/furniture-apple-leather/ (Accessed: August 28, 2020). Mautner, A., Lee, K.-Y., Tammelin, T., Mathew, A. P., Nedoma, A. J., Li, K. and Bismarck, A. (2015) “Cellulose nanopapers as tight aqueous ultra-filtration membranes,” Reactive and Functional Polymers , 86, pp. 209–214. doi: 10.1016/j.reactfunctpolym.2014.09.014. Milionis, A., Bayer, I. S. and Loth, E. (2016) “Recent advances in oil-repellent surfaces,” International Materials Reviews , 61(2), pp. 101–106. doi: 10.1080/09506608.2015.1116492. Mishra, R. K., Sabu, A. and Tiwari, S. K. (2018) “Materials chemistry and the futurist eco-friendly applications of nanocellulose: Status and prospect,” Journal of Saudi Chemical Society . doi: 10.1016/j.jscs.2018.02.005. Miyamoto, H., Tsuduki, M., Ago, M., Yamane, C., Ueda, M. and Okajima, K. (2014) “Influence of dyestuffs on the crystallinity of a bacterial cellulose and a regenerated cellulose,” Textile Research Journal , 84(11), pp. 1147–1158. doi: 10.1177/0040517513517960. Mizuno, M., Kamiya, Y., Katsuta, T., Oshima, N., Nozaki, K. and Amano, Y. (2012) “Creation of bacterial cellulose-fabric complexed material,” SEN’I GAKKAISHI , 68(2), pp. 42–47. Modern Meadow (2020) Technology - Modern Meadow , Modern Meadow . Available at: https://www.modernmeadow.com/technology (Accessed: September 2, 2020). Mohd, N. H., Farahein, N., Ismail, H., Zahari, J. I., Farahhanim, W., Kargarzadeh, H., Ramli, S., Ahmad, I., Yarmo, M. A. and Othaman, R. (2016) “Effect of aminosilane modification on nanocrystalline cellulose properties,” Journal of Nanomaterials , 2016. Mondal, S., Pal, S., Bal, R. and Maity, J. (2018) “Fabrication of two sites hydrophobicity on cotton surface – a fluoropolymerization approach,” Journal of Adhesion Science and Technology , 4243, pp. 1–10. doi: 10.1080/01694243.2018.1458407. Mukherjee, T., Rimal, S., Koskey, S., Chyan, O., Singh, K. J. and Myers, A. M. (2013) “Bonding structure of model fluorocarbon polymer residue determined by functional group specific chemical derivatization,” ECS Solid State Letters , 2(3), pp. 11–14. doi: 10.1149/2.008303ssl. Mukhopadhyay, A., Preet, A. and Midha, V. (2018) “Moisture transmission behaviour of individual component and multi-layered fabric with sweat and pure water,” Journal of the Textile Institute , 109(3), pp. 383–392. doi: 10.1080/00405000.2017.1348435. Naeem, M. A., Alfred, M., Saba, H., Siddiqui, Q., Naveed, T. and Shahbaz, U. (2019) “A preliminary study on the preparation of seamless tubular bacterial nanocomposite fabrics,” Journal of Composite Materials , 53(26–27). doi: 10.1177/0021998319842295. Nam, C. and Lee, Y.-A. (2016) “RETHINK II. Kombucha Shoes for Scarlett and Rhett,” in International Textile and Apparel Association (ITAA) Annual Conference Proceedings , pp. 1–2. Nasr, A. I. (2017) “Influence of some mechanical finishing processes on manufactured leather properties,” Majalah Kulit, Karet, dan Plastik , 33(2), pp. 99–107. doi: 10.20543/mkkp.v33i2.3139. Ng, A. (2017) “Grown microbial 3D fiber art, Ava: Fusion of traditional art with technology,” in
Chapter 8 – References 113 International Symposium on Wearable Computers, ISWC . Maui, pp. 209–214. doi: 10.1145/3123021.3123069. Ng, F. M. C. and Wang, P. W. (2016) “Natural self-grown fashion from bacterial cellulose: A paradigm shift design approach in fashion creation,” The Design Journal , 19(6), pp. 837–855. doi: 10.1080/14606925.2016.1208388. Ng, M. C. F. and Wang, W. (2015) “A study of the receptivity to bacterial cellulosic pellicle for fashion,” Research Journal of Textile and Apparel , 19(4), pp. 65–69. doi: 10.1108/RJTA-19-04-2015-B007. Nisoa, M. and Wanichapichart, P. (2010) “Surface hydrophobic modification of cellulose membranes by plasma-assisted deposition of hydrocarbon films,” Songklanakarin Journal of Science and Technology , 32(1), pp. 97–101. doi: 10.1016/j.surfcoat.2004.10.013. Nogi, M. and Yano, H. (2008) “Transparent nanocomposites based on cellulose produced by bacteria offer potential innovation in the electronics device industry,” Advanced Materials , 20, pp. 1849–1852. doi: 10.1002/adma.200702559. Nunez, F. U., Santiago, E. V. and Lopez, S. H. (2008) “Structural, thermal and morphological characterization of UV-graft polymerization of acrylated-epoxidized soybean oil onto goat leather,” Chemistry & Chemical Technology , 2(3), pp. 191–197. Oliveira, F. R., Fernandes, M., Carneiro, N. and Pedro Souto, A. (2013) “Functionalization of wool fabric with phase-change materials microcapsules after plasma surface modification,” Journal of Applied Polymer Science , 128(5). doi: 10.1002/app.38325. Padrão, J., Gonçalves, S., Silva, J. P., Sencadas, V., Lanceros-Méndez, S., Pinheiro, A. C., Vicente, A. A., Rodrigues, L. R. and Dourado, F. (2016) “Bacterial cellulose-lactoferrin as an antimicrobial edible packaging,” Food Hydrocolloids , 58, pp. 126–140. doi: 10.1016/j.foodhyd.2016.02.019. Palmleather (2017) Palmleather - Our story , Palmleather . Available at: http://palmleather.nl/?page_id=1028 (Accessed: June 1, 2017). Paquien, J. N., Galy, J., Gérard, J. F. and Pouchelon, A. (2005) “Rheological studies of fumed silicapolydimethylsiloxane suspensions,” Colloids and Surfaces A: Physicochemical and Engineering Aspects , 260(1–3), pp. 165–172. doi: 10.1016/j.colsurfa.2005.03.003. Peters, A. (2016) This beautiful carbon-neutral “Leather” is grown from mushrooms , Fast Company . Available at: https://www.fastcompany.com/3062236/this-beautiful-carbon-neutral-leather-is-grownfrom-mushrooms (Accessed: October 11, 2017). Pinto, E. R. P., Barud, H. S., Silva, R. R., Palmieri, M., Polito, W. L., Calil, V. L., Cremona, M., Ribeiro, S. J. L. and Messaddeq, Y. (2015) “Transparent composites prepared from bacterial cellulose and castor oil based polyurethane as substrates for flexible OLEDs,” Journal of Materials Chemistry C , 3(44), pp. 11581–11588. doi: 10.1039/c5tc02359a. Pleumphon, C., Thiangtham, S., Pechyen, C., Manuspiya, H. and Ummartyotin, S. (2017) “Development of conductive bacterial cellulose composites: An approach to bio-based substrates for solar cells,” Journal of Biobased Materials and Bioenergy , 11(4), pp. 321–329. doi: 10.1166/jbmb.2017.1686. Pommet, M., Juntaro, J., Heng, J. Y. Y., Mantalaris, A., Lee, A. F., Wilson, K., Kalinka, G., Shaffer, M. S. P. and Bismarck, A. (2008) “Surface modification of natural fibers using bacteria: Depositing bacterial cellulose onto natural fibers to create hierarchical fiber reinforced nanocomposites,” Biomacromolecules , 9(6), pp. 1643–1651. doi: 10.1021/bm800169g. Portela, R., Leal, C. R., Almeida, P. L. and Sobral, R. G. (2019) “Bacterial cellulose: a versatile biopolymer
Chapter 8 – References 114 for wound dressing applications,” Microbial Biotechnology , 12(4), pp. 586–610. doi: 10.1111/17517915.13392. Potivara, K. and Phisalaphong, M. (2019) “Development and characterization of bacterial cellulose reinforced with natural rubber,” Materials , 12(14). doi: 10.3390/ma12142323. Pradipasena, P., Chollakup, R. and Tantratian, S. (2018) “Formation and characterization of BC and BCpaper pulp films for packaging application,” Journal of Thermoplastic Composite Materials , 31(4), pp. 500–513. doi: 10.1177/0892705717712633. Radhakrishnan, T. S. (2005) “Thermal degradation of poly(dimethylsilylene) and poly(tetramethyldisilylene-co-styrene),” Journal of Applied Polymer Science , 99, pp. 2679–2686. doi: 10.1002/app.22813. Rajwade, J. M., Paknikar, K. M. and Kumbhar, J. V. (2015) “Applications of bacterial cellulose and its composites in biomedicine,” Applied Microbiology and Biotechnology , 99(6), pp. 2491–2511. doi: 10.1007/s00253-015-6426-3. Ramamoorthy, S. K., Kundu, C. K., Adekunle, K., Bashir, T. and Skrifvars, M. (2014) “Properties of green composites with regenerated cellulose fiber and soybean-based thermoset for technical applications,” Journal of Reinforced Plastics and Composites , 33(2), pp. 193–201. doi: 10.1177/0731684413504325. Ramamoorthy, S. K., Skrifvars, M., Alagar, R. and Akhtar, N. (2018) “End-of-life textiles as reinforcements in biocomposites,” Journal of Polymers and the Environment , 26, pp. 487–498. doi: 10.1007/s10924017-0965-x. Rathinamoorthy, R., Aarthi, T., Aksaya Shree, C. A., Haridharani, P., Shruthi, V. and Vaishnikka, R. L. (2019) “Development and characterization of self-assembled bacterial cellulose nonwoven film,” Journal of Natural Fibers . doi: 10.1080/15440478.2019.1701609. Raut, A. (2019) Malai: A sustainable, vegan alternative to leather , Architectural Digest . Available at: https://www.architecturaldigest.in/content/malai-a-sustainable-vegan-alternative-to-leather/ (Accessed: September 2, 2020). Retegi, A., Algar, I., Martin, L., Altuna, F., Stefani, P., Zuluaga, R., Gañán, P. and Mondragon, I. (2012) “Sustainable optically transparent composites based on epoxidized soy-bean oil (ESO) matrix and high contents of bacterial cellulose (BC),” Cellulose , 19(1), pp. 103–109. doi: 10.1007/s10570-011-9598-8. Riccio, C. (2017) Muskin, the vegetable leather made from mushrooms , LifeGate . Available at: http://www.lifegate.com/people/lifestyle/muskin-leather-mushrooms (Accessed: November 10, 2017). Rixtel, R. van (2019) Lino leather , Dutch Design Daily . Available at: dutchdesigndaily.com/completeoverview/lino-leather/ (Accessed: September 1, 2020). Robinson, M. (2016) Everything you own could one day be made from mushrooms , Business Insider . Available at: http://www.businessinsider.com/mycoworks-2016-7 (Accessed: November 10, 2017). Rojas-Downing, M. M., Nejadhashemi, A. P., Harrigan, T. and Woznicki, S. A. (2017) “Climate change and livestock: Impacts, adaptation, and mitigation,” Climate Risk Management , 16, pp. 145–163. doi: 10.1016/j.crm.2017.02.001. Rotor, A. V (2017) The making of nata de coco shoes , avrotor . Available at: http://avrotor.blogspot.com/2017/12/the-making-of-nata-de-coco-shoes.html (Accessed: November 6, 2017). Ruan, C., Zhu, Y., Zhou, X., Abidi, N., Hu, Y. and Catchmark, J. M. (2016) “Effect of cellulose crystallinity
Chapter 8 – References 115 on bacterial cellulose assembly,” Cellulose , 23(6), pp. 3417–3427. doi: 10.1007/s10570-016-1065-0. Sá, C. A. M. P. de (2011) “WO 2011149370 A1 - Cork fabric and process for the production thereof.” Available at: http://www.google.com/patents/WO2011149370A1?cl=en. Sai, H., Fu, R., Xing, L., Xiang, J., Li, Z., Li, F. and Zhang, T. (2015) “Surface modification of bacterial cellulose aerogels’ web-like skeleton for oil/water separation,” ACS Applied Materials and Interfaces , 7(13), pp. 7373–7381. doi: 10.1021/acsami.5b00846. Sai, H., Xing, L., Xiang, J., Cui, L., Jiao, J., Zhao, C., Li, Z., Li, F. and Zhang, T. (2014) “Flexible aerogels with interpenetrating network structure of bacterial cellulose-silica composite from sodium silicate precursor via freeze drying process,” RSC Advances , 4(57), pp. 30453–30461. doi: 10.1039/C4RA02752C. Saini, S., Belgacem, M. N., Salon, M.-C. B. and Bras, J. (2016) “Non leaching biomimetic antimicrobial surfaces via surface functionalisation of cellulose nanofibers with aminosilane,” Cellulose , 23(1), pp. 795–810. doi: 10.1007/s10570-015-0854-1. Saithai, P., Lecomte, J., Dubreucq, E. and Tanrattanakul, V. (2013) “Effects of different epoxidation methods of soybean oil on the characteristics of acrylated epoxidized soybean oil-co-poly(methyl methacrylate) copolymer,” Express Polymer Letters , 7(11), pp. 910–924. doi: 10.3144/expresspolymlett.2013.89. Salarbashi, D., Bazeli, J. and Tafaghodi, M. (2019) “Environment-friendly green composites based on soluble soybean polysaccharide: A review,” International Journal of Biological Macromolecules , 122, pp. 216–223. doi: 10.1016/j.ijbiomac.2018.10.110. Santos, S. M., Carbajo, J. M., Gómez, N., Quintana, E., Ladero, M., Sanchez, A., Chinga-Carrasco, G. and Villar, J. C. (2016) “Use of bacterial cellulose in degraded paper restoration. Part II: application on real samples,” Journal of Materials Chemistry , 51, pp. 1553–1561. doi: 10.1007/s10853-015-9477-z. Sathish, M., Madhan, B., Sreeram, K. J., Rao, J. R. and Nair, B. U. (2016) “Alternative carrier medium for sustainable leather manufacturing - a review and perspective,” Journal of Cleaner Production , 112, pp. 49–58. doi: 10.1016/j.jclepro.2015.06.118. Schenk, A. K. (2014) Study of the impact of the nonwoven substrate formation on artificial leather . North Carolina State University. Scherner, M., Reutter, S., Klemm, D., Sterner-Kock, A., Guschlbauer, M., Richter, T., Langebartels, G., Madershahian, N., Wahlers, T. and Wippermann, J. (2014) “In vivo application of tissue-engineered blood vessels of bacterial cellulose as small arterial substitutes: Proof of concept?,” Journal of Surgical Research , 189(2), pp. 340–347. doi: 10.1016/j.jss.2014.02.011. Schorn & Groh (2020) NUO. Real wood as soft as leather. , Schorn & Groh GmbH . Available at: https://en.sg-veneers.com/products/nuo-real-smooth-wood.html%0AThe (Accessed: September 15, 2020). Senoz, E., Stanzione, J. F., Reno, K. H., Wool, R. P. and Miller, M. E. N. (2013) “Pyrolyzed chicken feather fibers for biobased composite reinforcement,” Journal of Applied Polymer Science , 128(2), pp. 983–989. doi: 10.1002/app.38163. Shah, N., Ul-Islam, M., Khattak, W. A. and Park, J. K. (2013) “Overview of bacterial cellulose composites: A multipurpose advanced material,” Carbohydrate Polymers , 98(2), pp. 1585–1598. doi: 10.1016/j.carbpol.2013.08.018. Shao, W., Wu, J., Liu, H., Ye, S., Jiang, L. and Liu, X. (2017) “Novel bioactive surface functionalization of
Chapter 8 – References 116 bacterial cellulose membrane,” Carbohydrate Polymers , 178, pp. 270–276. doi: 10.1016/j.carbpol.2017.09.045. Shim, E. and Kim, H. R. (2019) “Coloration of bacterial cellulose using in situ and ex situ methods,” Textile Research Journal , 89(7), pp. 1297–1310. doi: 10.1177/0040517518770673. Sick-Leitner, M. (2015) SOYA C(O)U(L)TURE – Useful Things arise out of Waste , Ars Electronica Blog . Available at: https://ars.electronica.art/aeblog/en/2015/09/30/soya-coulture/ (Accessed: September 14, 2020). Silva, S. P., Sabino, M. A., Fernandes, E. M., Correlo, V. M., Boesel, L. F. and Reis, R. L. (2005) “Cork: properties, capabilities and applications,” International Materials Reviews , 50(6), pp. 345–365. doi: 10.1179/174328005X41168. Song, J. E., Cavaco-Paulo, A., Silva, C. and Kim, H. R. (2020) “Improvement of bacterial cellulose nonwoven fabrics by physical entrapment of lauryl gallate oligomers,” Textile Research Journal , 90(2), pp. 166–178. doi: 10.1177/0040517519862886. Song, J. E., Silva, C., Cavaco-Paulo, A. M. and Kim, H. R. (2019) “Functionalization of bacterial cellulose nonwoven by poly(Fluorophenol) to improve its hydrophobicity and durability,” Frontiers in Bioengineering and Biotechnology , 7, pp. 1–10. doi: 10.3389/fbioe.2019.00332. Song, J. E., Su, J., Noro, J., Cavaco-Paulo, A., Silva, C. and Kim, H. R. (2018) “Bio-coloration of bacterial cellulose assisted by immobilized laccase,” AMB Express , 8(19). doi: 10.1186/s13568-018-0552-0. Sousa, A. F., Ferreira, S., Lopez, A., Borges, I., Pinto, R. J. B., Silvestre, A. J. D. and Freire, C. S. R. (2017) “Thermosetting AESO-bacterial cellulose nanocomposite foams with tailored mechanical properties obtained by Pickering emulsion templating,” Polymer , 118, pp. 127–134. doi: 10.1016/j.polymer.2017.04.073. Soykeabkaew, N., Sian, C., Gea, S., Nishino, T. and Peijs, T. (2009) “All-cellulose nanocomposites by surface selective dissolution of bacterial cellulose,” Cellulose , 16(3), pp. 435–444. doi: 10.1007/s10570-009-9285-1. Stewart, J. (2020) Two men created “leather” from cactus to save animals and the environment , My Modern Met . Available at: https://mymodernmet.com/vegan-cactus-leather-desserto/ (Accessed: August 25, 2020). Sudha, T. B., Thanikaivelan, P., Aaron, K. P., Krishnaraj, K. and Chandrasekaran, B. (2009) “Comfort, chemical, mechanical, and structural properties of natural and synthetic leathers used for apparel,” Journal of Applied Polymer Science , 114, pp. 1761–1767. doi: 10.1002/app. Sun, Y., Meng, C., Zheng, Y., Wang, Y., Qiao, K., Yue, L., Xie, Y. and He, W. (2018) “The effects of two biocompatible plasticizers on the performance of dry bacterial cellulose membrane: a comparative study,” Cellulose , 25, pp. 5893–5908. doi: 10.1007/s10570-018-1968-z. Sureshkumar, P. S., Thanikaivelan, P., Phebe, K., Krishnaraj, K., Jagadeeswaran, R. and Chandrasekaran, B. (2012) “Investigations on structural, mechanical, and thermal properties of pineapple leaf fiber-based fabrics and cow softy leathers: An approach toward making amalgamated leather products,” Journal of Natural Fibers , 9(1), pp. 37–50. doi: 10.1080/15440478.2012.652834. Tamilselvi, A., Jayakumar, G. C., Sri Charan, K., Sahu, B., Deepa, P. R., Kanth, S. V. and Kanagaraj, J. (2019) “Extraction of cellulose from renewable resources and its application in leather finishing,” Journal of Cleaner Production , 230, pp. 694–699. doi: 10.1016/j.jclepro.2019.04.401. Tang, K. P. M., Kan, C. W. and Fan, J. T. (2014) “Evaluation of water absorption and transport property
Chapter 8 – References 117 of fabrics,” Textile Progress , 46(1), pp. 1–132. doi: 10.1080/00405167.2014.942582. Tang, L., Han, J., Jiang, Z., Chen, S. and Wang, H. (2015) “Flexible conductive polypyrrole nanocomposite membranes based on bacterial cellulose with amphiphobicity,” Carbohydrate Polymers , 117, pp. 230– 235. doi: 10.1016/j.carbpol.2014.09.049. Temmink, R., Baghaei, B. and Skrifvars, M. (2018) “Development of biocomposites from denim waste and thermoset bio-resins for structural applications,” Composites Part A: Applied Science and Manufacturing , 106, pp. 59–69. doi: 10.1016/j.compositesa.2017.12.011. Tian, Y., Ina, M., Cao, Z., Sheiko, S. S. and Dobrynin, A. V (2018) “How to measure work of adhesion and surface tension of soft polymeric materials,” Macromolecules , 51(11), pp. 4059–4067. doi: 10.1021/acs.macromol.8b00738. Tomé, L. C., Brandão, L., Mendes, A. M., Silvestre, A. J. D., Pascoal, C., Alessandro, N., Freire, C. S. R. and Marrucho, I. M. (2010) “Preparation and characterization of bacterial cellulose membranes with tailored surface and barrier properties,” Cellulose , 17(6), pp. 1203–1211. doi: 10.1007/s10570-0109457-z. Tomita, Y., Tsuji, T. and Kondo, T. (2009) “Fabrication of microbial cellulose nanofiber network sheets hydrophobically enhanced by introduction of a heat-printed surface,” Sen-I Gakkaishi , 65(2), pp. 73–79. Tu, C. (2016) The fungi in your future , Science Friday . Available at: https://www.sciencefriday.com/articles/the-fungi-in-your-future/ (Accessed: October 11, 2017). Tyurin, I., Getmantseva, V., Andreeva, E. and Kashcheev, O. (2019) “The study of the molding capabilities of bacterial cellulose,” in AUTEX 2019 - 19th World Textile Conference on Textiles at the Crossrorads . Ghent. Available at: https://ojs.ugent.be/autex/article/view/11745/11183. Ugbaja, M. I., Ejila, A., Mamza, P. A. and Mbada, I. N. (2016) “Water vapour permeability and wet rub fastness of finished leathers - Effect of acrylic polymer dispersion formulations,” Science Journal of Chemistry , 4(2), pp. 14–18. doi: 10.11648/j.sjc.20160402.11. United Nations (2015) Transforming our world: the 2030 Agenda for Sustainable Development . New York. Available at: https://www.un.org/ga/search/view_doc.asp?symbol=A/RES/70/1&Lang=E. Vegea (2017) VEGEA® - Innovative biomaterials created from wine , Vegea . Available at: http://www.vegeacompany.com/en/ (Accessed: November 10, 2017). Wahid, F., Hu, X., Chu, L., Jia, S., Xie, Y. and Zhong, C. (2019) “Development of bacterial cellulose/chitosan based semi-interpenetrating hydrogels with improved mechanical and antibacterial properties,” International Journal of Biological Macromolecules , 122, pp. 380–387. doi: 10.1016/j.ijbiomac.2018.10.105. Wan, Y. Z., Luo, H., He, F., Liang, H., Huang, Y. and Li, X. L. (2009) “Mechanical, moisture absorption, and biodegradation behaviours of bacterial cellulose fibre-reinforced starch biocomposites,” Composites Science and Technology , 69(7–8), pp. 1212–1217. doi: 10.1016/j.compscitech.2009.02.024. Wan, Z., Wang, L., Ma, L., Sun, Y. and Yang, X. (2017) “Controlled hydrophobic biosurface of bacterial cellulose nanofibers through self-assembly of natural zein protein,” ACS Biomaterials Science & Engineering , 3(8), pp. 1595–1694. doi: 10.1021/acsbiomaterials.7b00116. Wang, J., Tavakoli, J. and Tang, Y. (2019) “Bacterial cellulose production, properties and applications with different culture methods – A review,” Carbohydrate Polymers , 219, pp. 63–76. doi: 10.1016/j.carbpol.2019.05.008. Wang, S. (2013) Redox-initiated adiabatic emulsion polymerization . Lehigh University.
Chapter 8 – References 118 Wang, S., Jiang, F., Xu, X., Kuang, Y., Fu, K., Hitz, E. and Hu, L. (2017) “Super-strong, super-stiff macrofibers with aligned, long bacterial cellulose nanofibers,” Advanced Materials , 29(35), pp. 1–8. doi: 10.1002/adma.201702498. Wei, B., Yang, G. and Hong, F. (2011) “Preparation and evaluation of a kind of bacterial cellulose dry films with antibacterial properties,” Carbohydrate Polymers , 84, pp. 533–538. doi: 10.1016/j.carbpol.2010.12.017. Wei, G., Xu, H., Chen, L., Li, Z. and Liu, R. (2019) “Isosorbide-based high performance UV-curable reactive diluents,” Progress in Organic Coatings , 126, pp. 162–167. doi: 10.1016/j.porgcoat.2018.10.028. Wei, L. and Mcdonald, A. G. (2016) “A review on grafting of biofibers for biocomposites,” Materials , 9(303). doi: 10.3390/ma9040303. Wiśniewska, M., Chibowski, S., Urban, T. and Terpiłowski, K. (2019) “Investigations of chromium(III) oxide removal from the aqueous suspension using the mixed flocculant composed of anionic and cationic polyacrylamides,” Journal of Hazardous Materials , 368, pp. 378–385. doi: 10.1016/j.jhazmat.2019.01.068. Wood, D., Hang, L. and Salusso, C. J. (2015) “Production and characterization of bacterial cellulose fabrics,” in International Textile and Apparel Association (ITAA) Annual Conference Proceedings . Santa Fe, pp. 11–13. Wool, R. (2013) “US 2013/0337711 A1 - Composites having leather-like characteristics.” Wu, S. (1971) “Calculation of interfacial tension in polymer systems,” Journal of Polymer Science Part C: Polymer Symposia , 34(1), pp. 19–30. doi: 10.1002/polc.5070340105. Wu, X., Li, J., Li, G., Ling, L., Zhang, G., Sun, R. and Wong, C.-P. (2018) “Heat-triggered poly(siloxaneurethane)s based on disulfide bonds for self-healing application,” Journal of Applied Polymer Science , 46532, pp. 1–9. doi: 10.1002/app.46532. Wu, Z., Chen, S., Wu, R., Sheng, N., Zhang, M., Ji, P. and Wang, H. (2020) “Top-down peeling bacterial cellulose to high strength ultrathin films and multifunctional fibers,” Chemical Engineering Journal , 391, p. 123527. doi: 10.1016/j.cej.2019.123527. Wu, Z. Y., Liang, H. W., Chen, L. F., Hu, B. C. and Yu, S. H. (2016) “Bacterial cellulose: A robust platform for design of three dimensional carbon-based functional nanomaterials,” Accounts of Chemical Research , 49(1), pp. 96–105. doi: 10.1021/acs.accounts.5b00380. Xu, Q., Fan, L., Yuan, Y., Wei, C., Bai, Z. and Xu, J. (2016) “All-solid-state yarn supercapacitors based on hierarchically structured bacterial cellulose nanofiber-coated cotton yarns,” Cellulose , 23(6), pp. 3987– 3997. doi: 10.1007/s10570-016-1086-8. Xu, X., Jagota, A., Paretkar, D. and Hui, C. (2016) “Surface tension measurement from the indentation of clamped thin films,” Soft Matter , 12, pp. 5121–5126. doi: 10.1039/c6sm00584e. Yang, Q., Ma, H., Dai, Z., Wang, J., Dong, S., Shen, J. and Dong, J. (2017) “Improved thermal and mechanical properties of bacterial cellulose with the introduction of collagen,” Cellulose , 24(9), pp. 3777– 3787. doi: 10.1007/s10570-017-1366-y. Yao, J., Chen, S., Chen, Y., Wang, B., Pei, Q. and Wang, H. (2017) “Macrofibers with high mechanical performance based on aligned bacterial cellulose nanofibers,” ACS Applied Materials & Interfaces , 9(24), pp. 20330–20339. doi: 10.1021/acsami.6b14650. Yim, S. M., Song, J. E. and Kim, H. R. (2017) “Production and characterization of bacterial cellulose
Chapter 8 – References 119 fabrics by nitrogen sources of tea and carbon sources of sugar,” Process Biochemistry , 59, pp. 26–36. doi: 10.1016/j.procbio.2016.07.001. Yorgancioglu, A., Başaran, B. and Sancakli, A. (2020) Value addition to leather industry wastes and byproducts: Hydrolyzed collagen and collagen peptides , IntechOpen . doi: 10.5772/intechopen.92699. Yousefi, B., Gharehaghaji, A. A., Asghar, A. and Jeddi, A. (2018) “The combined effect of wrinkles and noncircular shape of fibers on wetting behavior of electrospun cellulose acetate membranes,” Journal of Polymer Science Part B: Polymer Physics , 56, pp. 1012–1020. doi: 10.1002/polb.24617. Yu, B., Cheng, H., Zhuang, W., Zhu, C., Wu, J., Niu, H., Liu, D., Chen, Y. and Ying, H. (2018) “Stability and repeatability improvement of horseradish peroxidase by immobilization on amino-functionalized bacterial cellulose,” Process Biochemistry , 79, pp. 40–48. doi: 10.1016/j.procbio.2018.12.024. Zahid, M., Heredia-Guerrero, J. A., Athanassiou, A. and Bayer, I. S. (2017) “Robust water repellent treatment for woven cotton fabrics with eco-friendly polymers,” Chemical Engineering Journal , 319, pp. 321–332. doi: 10.1016/j.cej.2017.03.006. Zargar, R., Nourmohammadi, J. and Amosbediny, G. (2015) “Preparation, characterization, and silanization of 3D microporous PDMS structure with properly sized pores for endothelial cell culture,” International Union of Biochemistry and Molecular Biology , 63(2), pp. 190–199. doi: 10.1002/bab.1371. Zengin, G., Sardroudi, S. P., Bitlisli, B. O. and Zengin, A. C. A. (2016) “Effect of various tanning processes on characteristics of lining leathers,” in ICAMS 2016 - Proceedings of the 6th International Conference on Advanced Materials and Systems . doi: 10.24264/icams-2016.iii.21. Zhang, C., Yan, M., Cochran, E. W. and Kessler, M. R. (2015) “Biorenewable polymers based on acrylated epoxidized soybean oil and methacrylated vanillin,” Materials Today Communications , 5, pp. 18–22. doi: 10.1016/j.mtcomm.2015.09.003. Zhang, W., Kalulu, M., Wang, X.-H., Xia, X.-K., Han, X.-L. and Jiang, Y. (2018) “Reverse hydrophobic PDMS surface to hydrophilic by 1-step hydrolysis reaction,” Polymers for Advanced Technologies , 29(7), pp. 2103–2109. doi: 10.1002/pat.4319. Zhao, W., Zhang, X., Tian, C. and Gao, Z. (2015) “Analysis of wetting characteristics on microstructured hydrophobic surfaces for the passive containment cooling system,” Science and Technology of Nuclear Installations , 2015, p. 6. doi: 10.1155/2015/652731. Zhong, C. (2020) “Industrial-scale production and applications of bacterial cellulose,” Frontiers in Bioengineering and Biotechnology , 8, pp. 1–19. doi: 10.3389/fbioe.2020.605374. Zhu, J., Chandrashekhara, K., Flanigan, V. and Kapila, S. (2004) “Curing and mechanical characterization of a soy-based epoxy resin system,” Journal of Applied Polymer Science , 91, pp. 3513–3518. doi: 10.1002/app.13571. Zürbig, C., Kruse, H.-H. and Buchkremer, K. (2015) “Leather imitates,” ULLMANN’S , p. 13. doi: 10.1002/14356007.a15_283.pub2.