Development of Biocomposite Superabsorbent Nanomaterials: Effect of Processing Technique

Depósito de investigación de la Universidad de Sevilla https://idus.us.es/ Esta es la versión aceptada del artículo publicado en: This is a accepted manuscript of a paper published in: Journal of Polymers and the Environment ( 2018): 26, 4013–4018 DOI: https://doi.org/10.1007/s10924-018-1262-z Copyright: © 2025 Springer Nature El acceso a la versión publicada del artículo puede requerir la suscripción de la revista. Access to the published version may require subscription. “This version of the article has been accepted for publication, after peer review (when applicable) and is subject to Springer Nature’s AM terms of use, but is not the Version of Record and does not reflect post-acceptance improvements, or any corrections. The Version of Record is available online at: http://dx.doi.org /10.1007/s10924-018-1262-z” 1 Development of biocomposite superabsorbent nanomaterials: Effect of processing technique M.Felix1, I. Martínez2, J.M. Aguilar1, A. Guerrero1 1 University of Seville, Escuela Politécnica Superior, C/ Virgen de África, 7, Seville (Spain). 2Dpto. Ingeniería Química, Centro de Investigación en Tecnología de Productos y Procesos Químicos (Pro2TecS), Universidad de Huelva-Campus Excelencia CeiA3, Campus El Carmen, 21071, Huelva (Spain). *M. FELIX Departamento de Ingeniería Química, Universidad de Sevilla, Escuela Politécnica Superior, 41011 Sevilla (Spain) E-mail: [email protected] Tel: +34 954557179; fax: +34 954556447. 2 Abstract Nanoclay particles have been usually introduced into protein-based bioplastics to obtain composite materials, showing enhanced mechanical properties. However, the addition of partially exfoliated nanoclay particles in these protein matrices may also involve an increase of others properties such as water absorption capacity, which may lead to the obtention of super absorbent biodegradable materials. Processing technologies exerted a remarkable influence on the technofunctional properties of the soy-based bioplastics studied in this research. On the one hand, extrusion technique led to bioplastics which showed enhanced mechanical properties. On the other hand, injection moulding technique yielded to non-exfoliated nanoclay particles within the protein matrix, which involved improvements of water absorption capacity. The development of superabsorbent protein-based biodegradable materials implied a deep knowledge of physicochemical properties of proteins and processing conditions of bioplastics. Extrusion or injection moulding techniques could be selected to obtain tailored protein-based bioplastics with enhanced properties. Keywords: Biopolymer processing; Mechanical properties; Montmorillonite; Proteins; Water absorption capacity 3 Introduction Society is highly interested in substituting petroleum-based plastics by other alternative materials to diminish human footprint [1]. These alternative materials should have suitable mechanical properties, and their use should reduce environmental damages caused by existing plastic materials [2]. In this sense, plastics made from renewable sources may be considered as an alternative to satisfy the above-mentioned social requirements [3, 4]. Bio-based materials are these ones derived, at least partially, from a renewable source (i.e. biomass). Proteins, polysaccharides and lipids, among others, have been postulated as excellent candidates for developing bio-based plastic materials which may exhibit suitable mechanical properties as well as consumer acceptation [5, 6]. Among these alternatives, soybean protein concentrates are coproducts from the soybean-oil industry since they are obtained during the extraction of oil from soybean seeds. This could be the cause of being the cheapest in global markets. Interestingly, these protein concentrates exhibit excellent functional properties. For instance, they have been previously used for the development of emulsions and gels [7, 8]. In addition, they show hydrophilic amino acids which could lead to superabsorbent properties [9]. However, mechanical and techno-functional properties of these bio-based systems may not be enough to substitute petroleum-based polymers [10]. Not only chemical reagents have been used to improve these properties such as sodium sulphite or urea [11–13], but also they could be improved by the use of fillers [14–16]. For instance, sodium montmorillonite (MMT-Na+) is a natural clay which is made up by microcrystalline silicate aggregated in thousand of layers [17, 18]. This phyllosilicate has been one of the most studied nanofillers in plastic industry. Their particles may increase both, mechanical and techno-functional properties of bioplastic obtained since they exhibit a high surface area and they can interact with protein chains. In addition, they are cheap and readily accessible [19, 20]. However, interactions between synthetic polymer chains and nanoclay particles have been proved to be crucial. The exfoliation of nanoclay particles dominates further mechanical and techno-functional properties of bio-based nanocomposite materials [21, 22]. In this sense, the processing technique selected must ensure a homogenous dispersion of nanoclays 4 into biopolymer matrices. Among the different alternatives available in polymer industry, there are two of special industrial interest: injection moulding and extrusion. On the one hand, injection moulding is one of the most versatile and used technique for polymer processing [21], this technique is particularly indicated for polymers that exhibit a typical thermoplastic behaviour. On the other hand, extrusion is widely used to manufacture synthetic polymers on commercial scale. This technique is preferred by plastic industry since it can be operated in continuous mode [23]. This work is devoted to clarify the relationship between processing technique (either injection moulding or extrusion) of soy-based biocomposites materials and techno-functional properties of biocomposites obtained. To achieve this objective, the focus was on: i) nanoclay structure, analysed by means of X-Ray; ii) mechanical features, tested by rheological measurements and iii) techno-functional properties analysed by means of water uptake capacity. Experimental Materials Soy Protein Isolated (SPI) Surpo500E was supplied by Protein Technologies International (Leper, Belgium). Dumas method was used to determine nitrogen content and protein content was expressed as %Nx6.25. Thus, the total protein content reach up to 910 ± 5 g·kg-1; ash and moisture content were 52 ± 1 g·kg-1 and 37 ± 5 g·kg-1, respectively. Glycerol (GL) was the only plasticizer used and it was purchased together with all other chemicals from Sigma-Aldrich (St. Louis, Missouri, USA). The clay (montmorillonite) introduced was Cloisite® Na+ (MMT-Na+), it was supplied by Southern Clay Products, Inc. (USA). Sample preparation Composites obtained by injection moulding (I-M) were formulated by adding 30 g·kg-1 nanoclay to blends containing 500 g·kg-1 SPI and 500 g·kg-1 glycerol. The injection moulding procedure was carried out in two separated stages. Firstly, blends were mixed at 25ºC and 50 rpm in a mixer which allows monitoring torque and temperature values (HaakePolylab QC; ThermoScientific, Germany). After the first mixing stage, bio-based composite materials were obtained using a MiniJet Piston Injection Moulding Systmem (ThermoHaake, Germany). Processing conditions 5 were fixed as follows: cylinder temperature (60 ºC), mould temperature (120 ºC), injection pressure (500 Pa for 20 s) and holding pressure (200 Pa for 300 s). Two different specimens were prepared by using different moulds: (1) 60×10×1 mm rectangular-shaped specimens used for dynamic mechanical analysis (DMA) and water absorption capacity and (2) dumb-bell-type specimens by ISO 527-1:2012 for analyzing tensile properties of samples. As for extruded biocomposites (Ex), the protein/plasticizer ratio and the amount of nanoclay used for them were exactly the same that those used for the samples obtained by injection moulding. The twin-screw extruder used was the EuroLab 16 (ThermoScientific, Massachusetts, USA). The barrel diameter is 16 mm and the ratio length/diameter (L/D) is 40. All samples were processed at a constant rotational speed of 100 rpm and with a specific set barrel temperature profile (50- 55-50-45-45-45-40-35-30-120ºC from hopper to die). An electrically heated sheet-shaped die was connected to the end of the extruder barrel to form the biocomposite as ribbon and sheets with thickness between 1.0 and 1.2 mm were obtained. The effective temperature of the dye was the same as the one used for the mould (120ºC). Methods Dynamic Mechanical Thermal Analysis (DMTA) Rheology of solid probes was carried out at 30 ºC by means of a RSA3 rheometer (TA Instruments, New Castle, USA) using a dual cantilever tool. Frequency sweep tests were performed from 0.02 to 20 Hz. Strain sweep tests were carried out prior to frequency sweep tests to determine the linear viscoelastic region (LVR). All frequency test were run at a constant strain value of 0.08%. Water uptake capacity Water uptake capacity (WUC) of these biocomposite materials was measured following the standard method ASTM D570 indicated for determining water absorption in synthetic polymers. Rectangular probes (60×10×1 mm) were used. Specimens were dried into an oven at 50 ± 2 ºC over 5-6 h (conditioning) to determine their dry weights. Afterwards, they were introduced into a specific volume of distilled water and weighed after 2 and 48h water immersion. Finally, they 6 were subjected to drying (reconditioning) into an oven containing silica gel at 60 ºC over 24 h and subsequently they were weighed to determine the soluble material loss. Eq. 1 shows the mathematical expression followed to determine water uptake capacity: 𝑊𝑊𝑊𝑊𝑊𝑊 = 𝑊𝑊𝑊𝑊𝑊𝑊 𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊ℎ𝑊𝑊 − 𝐼𝐼𝐼𝐼𝑊𝑊𝑊𝑊𝑊𝑊𝐼𝐼𝐼𝐼 𝐷𝐷𝐷𝐷𝐷𝐷𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊ℎ𝑊𝑊 𝐼𝐼𝐼𝐼𝑊𝑊𝑊𝑊𝑊𝑊𝐼𝐼𝐼𝐼 𝐷𝐷𝐷𝐷𝐷𝐷𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊ℎ𝑊𝑊 (1) X-Ray measurements The crystallinity of samples was studied using a D8 Discover device (BRUKE, Massachusetts, USA). The potential and intensity of the beam in these XRD studies were 40 kV, 30 mA, respectively, where Cu Kα radiation was used (λ=0.1516 nm). The step size selected for these experiments was 0.05º, whereas the scanning range (2θ) used was within 2 to 30°. Fourier Transform Infra-Red (FTIR) Fourier Transform Infra-Red (FTIR) measurements were performed using a Jasco FT4200 infrared spectrometer (JASCO Inc., Tokyo, Japan) equipped with an attenuated total reflectance (ATR) system. Biocomposite samples were loaded onto the ATR crystal area and the respective spectra obtained in the transmission mode over a scanning range of 550-4000 nm at a resolution of 4 nm. Differential Scanning Calorimetry (DSC) A calorimeter DSC Q20 equipped with an auto sampler unit (TA Instruments, USA) was used to perform DSC analysis. Samples were weight (5 - 10 mg) and they were placed into hermetic-sealed aluminium pans. The heating rate was 10 ºC/min, with a continuous flow of nitrogen (50 mL/min) was applied. Statistical analysis All measurements were carried out in representative triplicate. The average from the three replicates were plotted Results and Discussion The complex modulus (E*) and loss tangent (tan δ) as a function of frequency for biocomposites probes processed by injection moulding (I-M) or extrusion (Ex) were plotted in Figure 1. 7 As can be observed, complex modulus values range from 2·106 to 1·108 Pa. Moreover, they are not strongly frequency-dependent, supporting solid-like materials remains unaltered within the overall frequency interval studied. These values are in accordance with others obtained from other bio-based composite materials [11]. It is worth mentioning that G* values are affected by the processing technique used. Thus, values obtained by injection moulding are one order of magnitude lower than those obtained by extrusion processing. This different behaviour may be related to the fact that extrusion involves a higher shear in the initial dough-like material what would allow a higher protein crosslinking during the thermomechanical processing, as well as it would increase the exfoliation of nanoclay particles introduced [24]. As it is shown in Fig. 1, tan δ exhibit a low dependence on frequency and low values that is characteristic of solid materials. It may be also noticed that biocomposites processed by injection moulding show a soft minimum value for tan δ, related to the lower planarity of G” for this system. In this sense, the higher planarity found for biocomposites processed by extrusion suggests that these systems have higher structuration. Thus, this figure puts forward the improvements of mechanical properties of bioplastics obtained by extrusion compared to those obtained by I-M. Results obtained from water uptake capacity tests for soy-based biocomposites materials processed by injection moulding (I-M) or by extrusion (Ex) are plotted in Figure 2. These results are expressed as grams of water absorbed per kg of bioplatic after immersion in water for 2 or 24 hours. Soluble matter loss values for all the samples under study were also plotted in this figure. As may be observed, the WUC is remarkable high in all cases studied, regardless of the processing technique used. These results may be related to the presence of many hydrophilic groups in soy proteins [25]. However, the maximum value of WUC achieved strongly depends on the processing technique used. To understand the behaviour of these composites, we should describe three different assumptions for the nanoclay exfoliation, which depends on polymer/MMT-Na+ interactions [26]: 8 - If interactions are very weak, tactoids remain unaltered inside of polymer matrix. As a result, mechanical properties of the final material are not markedly different to those of the original polymer, and nanoclay particles act as a filler. - When there are moderate interactions, the clay interlayer expands its interstitial distance and protein chains can penetrate into the gaps between different layers. In this case, an intercalated structure is formed. - If there are strong interactions, the initial structure of the nanoclay is lost and nanoclay particles have been exfoliated. Among them, only the last assumption has been the one related to the overall improvements of mechanical properties of synthetic polymers [27]. According to mechanical properties showed in Figure 1, and the different relationship observed between soy protein and nanoclay particles, it could be concluded that when extrusion is used as processing technique a complete exfoliation of nanoclay particles take place, which may justify the remarkable increase in the complex modulus observed in Figure 1. The high values of water uptake capacity of obtained for composites processed by injection moulding, coupled with the fact that rheological properties showed in Figure 1 are not as high as those obtained from the extruded composites may suggest that nanoclay particles are not completely exfoliated in the biocomposites obtained by injection moulding technique (I-M). Thus, to elucidate whether or not nanoclay particles are completely exfoliated, X-Ray measurements were carried out to clarify the different crystalline phases present in these biocomposites. XRD diagrams for soy protein concentrate, MMT-Na+ dust, and probes obtained from injection moulding (I-M) or extrusion (Ex) processing were plotted in Figure 3. As may be observed, the diffractogram obtained for MMT-Na+ dust exhibits a strong peak at 7.24º, which corresponds to the interplanar spacing of MMT-Na+ tactoids. Moreover, soy protein exhibits two notable peaks which corresponds to the 7S and 11S subunits [28]. First of all, note that the peak numbered as 1 is present only in the composite obtained by injection moulding (I-M). Its low intensity is related to the fact that there is only 30 g·kg-1 of nanoclay in 15 soy protein isolate (SPI)-based adhesives. Ind Crops Prod 74:577–584 . doi: https://doi.org/10.1016/j.indcrop.2015.05.043 34. Wang L, Mogami S, Karasawa H, et al (2014) Preventive effect of rikkunshito on gastric motor function inhibited by l-dopa in rats. Peptides 55:136–144 . doi: https://doi.org/10.1016/j.peptides.2014.02.011 35. A Bunaciu A, Fleschin S, Y Aboul-Enein H (2014) Infrared Microspectroscopy Applications-Review. Curr Anal Chem 10:132–139 36. Fan F, Roos YH (2017) Glass Transition-Associated Structural Relaxations and Applications of Relaxation Times in Amorphous Food Solids: a Review. Food Eng Rev 9:257–270 . doi: 10.1007/s12393-017-9166-6 16 1. Blanke MM (2014) Reducing ethylene levels along the food supply chain: a key to reducing food waste? J Sci Food Agric 94:2357–2361 . 2. Stanzione J, La Scala J (2016) Sustainable polymers and polymer science: Dedicated to the life and work of Richard P. Wool. J Appl Polym Sci 133:n/a--n/a . 3. Plastics-Europe (2008) Safeguarding the Planet by, Reaching Out. http://www.plasticseurope.org/cust/documentrequest.aspx?DocID=493 4. Verbeek CJR, van den Berg LE (2011) Development of Proteinous Bioplastics Using Bloodmeal. J Polym Environ 19:1–10 . 5. Álvarez-Chávez CR, Edwards S, Moure-Eraso R, Geiser K (2012) Sustainability of biobased plastics: general comparative analysis and recommendations for improvement. J Clean Prod 23:47–56 . 6. Felix M, Perez-Puyana V, Romero A, Guerrero A (2016) Production and Characterization of Bioplastics Obtained by Injection Moulding of Various Protein Systems. J Polym Environ 1–10 . 7. Chove BE, Grandison AS, Lewis MJ (2002) Emulsifying properties of soy protein isolates obtained by microfiltration. J Sci Food Agric 82:267–272 . 8. Creusot N, Wierenga PA, Laus MC, et al (2011) Rheological properties of patatin gels compared with β-lactoglobulin, ovalbumin, and glycinin. J Sci Food Agric 91:253–261 . 9. Tian H, Wang Y, Zhang L, et al (2010) Improved flexibility and water resistance of soy protein thermoplastics containing waterborne polyurethane. Ind Crops Prod 32:13–20 . 10. Low A, Verbeek CJR, Lay MC (2014) Treating Bloodmeal with Peracetic Acid to Produce a Bioplastic Feedstock. Macromol Mater Eng 299:75–84 . 11. Felix M, Romero A, Cordobes F, Guerrero A (2015) Development of crayfish bio-based plastic materials processed by small-scale injection moulding. J Sci Food Agric 95:679– 687 . 17 12. Ture H, Gallstedt M, Kuktaite R, et al (2011) Protein network structure and properties of wheat gluten extrudates using a novel solvent-free approach with urea as a combined denaturant and plasticiser. Soft Matter 7:9416–9423 . 13. Jerez A, Partal P, Martinez I, et al (2005) Rheology and processing of gluten based bioplastics. Biochem Eng J 26:131–138 . 14. Günister E, Pestreli D, Ünlü CH, et al (2007) Synthesis and characterization of chitosan- MMT biocomposite systems. Carbohydr Polym 67:358–365 . 15. Strawhecker KE, Manias E (2000) Structure and properties of poly(vinyl alcohol)/Na+ montmorillonite nanocomposites. Chem Mater 12:2943–2949 . 16. Felix M, Martinez I, Romero A, et al (2018) Effect of pH and nanoclay content on the morphology and physicochemical properties of soy protein/montmorillonite nanocomposite obtained by extrusion. Compos Part B Eng 140:197–203 . 17. Chen Z, Feng R (2009) Preparation and characterization of poly(styrene-b-butadiene-b- styrene)/montmorillonite nanocomposites. Polym Compos 30:281–287 . 18. Türe H, Blomfeldt TOJ, Gällstedt M, Hedenqvist MS (2012) Properties of Wheat- Gluten/Montmorillonite Nanocomposite Films Obtained by a Solvent-Free Extrusion Process. J Polym Environ 20:1038–1045 . 19. Amin A, Ahmed EH, Sabaa MW, et al (2016) Preparation and evaluation of hyperbranched p-chloromethyl styrene polymers/montmorillonite clay nanocomposites as dielectric materials. Polym Bull 73:147–162 . 20. Hua J, Liu J, Wang X, et al (2017) Structure and Properties of a cis-1,4- Polybutadiene/Organic Montmorillonite Nanocomposite Prepared via In Situ Polymerization. J Macromol Sci Part B 56:451–461 . 21. B L, L J, J Z (2010) Development of Soy Protein/Poly (Lactic Acid) Bioplastics. In: GEPC (ed) Society of Plastic Engineers – Global Plastics Environmental Conference 18 22. Quigley JP, Baird DG (2015) Improved mechanical properties of organoclay/nylon 6 nanocomposites prepared via a supercritical carbon dioxide-aided, melt blending method. Polym Compos 36:527–537 . 23. Hietala M, Mathew AP, Oksman K (2013) Bionanocomposites of thermoplastic starch and cellulose nanofibers manufactured using twin-screw extrusion. Eur Polym J 49:950–956 . 24. Fu X, Qutubuddin S (2001) Polymer–clay nanocomposites: exfoliation of organophilic montmorillonite nanolayers in polystyrene. Polymer (Guildf) 42:807–813 . doi: 25. Jovanovich G, Puppo MC, Giner SA, Añón MC (2003) Water uptake by dehydrated soy protein isolates: Comparison of equilibrium vapour sorption and water imbibing methods. J Food Eng 56:331–338 . 26. Essawy HA, El-Sabbagh SH, Tawfik ME (2015) Novel interpenetrating amphiphilic Conetworks based on compatibilized NBR/SBR-montmorillonite composites: A study on the oil absorption characteristics. Polym Compos 36:1494–1501 . 27. Chivrac F, Pollett E, Schmutz M, Averous L (2008) New approach to elaborate exfoliated starch-based nanobiocomposites. Biomacromolecules 9:896–900 . 28. Peng IC, Quass DW, Dayton WR, Allen CE (1984) The physicochemical and functionalproperties of soybean 11s globulin - a Review. Cereal Chem 61:480–490 29. Cuadri AA, Romero A, Bengoechea C, Guerrero A (2017) Natural superabsorbent plastic materials based on a functionalized soy protein. Polym Test 58:126–134 . 30. Ulrichs T, Drotleff AM, Ternes W (2015) Determination of heat-induced changes in the protein secondary structure of reconstituted livetins (water-soluble proteins from hen’s egg yolk) by FTIR. Food Chem 172:909–920 . 31. Zohdi V, Whelan DR, Wood BR, et al (2015) Importance of Tissue Preparation Methods in FTIR Micro-Spectroscopical Analysis of Biological Tissues: “Traps for New Users.” PLoS One 10:1–11 . 19 32. Spada JC, Marczak LDF, Tessaro IC, Cardozo NSM (2015) Interactions between soy protein from water-soluble soy extract and polysaccharides in solutions with polydextrose. Carbohydr Polym 134:119–127 . 33. Liu H, Li C, Sun XS (2015) Improved water resistance in undecylenic acid (UA)-modified soy protein isolate (SPI)-based adhesives. Ind Crops Prod 74:577–584 . 34. Wang L, Mogami S, Karasawa H, et al (2014) Preventive effect of rikkunshito on gastric motor function inhibited by l-dopa in rats. Peptides 55:136–144 . 35. A Bunaciu A, Fleschin S, Y Aboul-Enein H (2014) Infrared Microspectroscopy Applications-Review. Curr Anal Chem 10:132–139 36. Fan F, Roos YH (2017) Glass Transition-Associated Structural Relaxations and Applications of Relaxation Times in Amorphous Food Solids: a Review. Food Eng Rev 9:257–270 . 20 Figure captions Figure 1. E* and tan δ for composites materials processed by injection moulding (I-M) or by extrusion (Ex) as a function of frequency Figure 2. Water uptake capacity and loss of soluble matter of samples, immersed in water at room temperature, after 2 and 48h Figure 3. XRD diagrams for soy protein concentrate, MMT-Na+ dust, and probes processed by injection moulding (I-M) or extrusion (Ex) Figure 4. FTIR spectra for probes processed by injection moulding (I-M) or extrusion (Ex) Figure 5. DSD measurements for probes processed by injection moulding (I–M) or extrusion (Ex) 21 Figure 1 22 Figure 2 23 Figure 3 24 Figure 4