International Journal of
Molecular Sciences
Article
Fabrication of Paper Sheets Coatings Based on
Chitosan/Bacterial Nanocellulose/ZnO with Enhanced
Antibacterial and Mechanical Properties
Joanna Jabło´nska 1,* , Magdalena Onyszko 2, Maciej Konopacki 1, Adrian Augustyniak 1,3 , Rafał Rakoczy 1
and Ewa Mijowska 2
Citation: Jabło´nska, J.; Onyszko, M.;
Konopacki, M.; Augustyniak, A.;
Rakoczy, R.; Mijowska, E. Fabrication
of Paper Sheets Coatings Based on
Chitosan/Bacterial Nanocellulose/
ZnO with Enhanced Antibacterial
and Mechanical Properties. Int. J. Mol.
Sci. 2021,22, 7383. https://doi.org/
10.3390/ijms22147383
Academic Editors: Iolanda Francolini,
Antonella Piozzi, Hitoshi Sashiwa
and Eric Guibal
Received: 17 May 2021
Accepted: 6 July 2021
Published: 9 July 2021
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
published maps and institutional affil-
iations.
Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
1Department of Chemical and Process Engineering, Faculty of Chemical Technology and Engineering,
West Pomeranian University of Technology in Szczecin, Piastow Ave. 42, 71-065 Szczecin, Poland;
2Department of Nanomaterials Physicochemistry, Faculty of Chemical Technology and Engineering,
West Pomeranian University of Technology in Szczecin, Piastow Ave. 49, 71-065 Szczecin, Poland;
3Chair of Building Materials and Construction Chemistry, Technische Universität Berlin,
Gustav-Meyer-Allee 25, 13355 Berlin, Germany
*Correspondence: [email protected]; Tel.: +48-605-393-602
Abstract:
Here, we designed paper sheets coated with chitosan, bacterial cellulose (nanofibers), and
ZnO with boosted antibacterial and mechanical activity. We investigated the compositions, with ZnO
exhibiting two different sizes/shapes: (1) rods and (2) irregular sphere-like particles. The proposed
processing of bacterial cellulose resulted in the formation of nanofibers. Antimicrobial behavior
was tested using E. coli ATCC
®
25922
™
following the ASTM E2149-13a standard. The mechanical
properties of the paper sheets were measured by comparing tearing resistance, tensile strength, and
bursting strength according to the ISO 5270 standard. The results showed an increased antibacterial
response (assigned to the combination of chitosan and ZnO, independent of its shape and size) and
boosted mechanical properties. Therefore, the proposed composition is an interesting multifunctional
mixture for coatings in food packaging applications.
Keywords: biopolymers; paper packaging; antimicrobial activity; nanoparticles
1. Introduction
The food packaging industry is a source of tons of plastic waste every year. It raises
environmental concerns about greenhouse gas emissions, a growing carbon footprint, and
the welfare of sea animals and birds [
1
–
4
]. Therefore, attempts to use more eco-friendly
materials, such as biopolymers, are intensified. Those materials can exhibit good properties
when incorporated into the mass of cellulose used for paper production or can be applied
as coatings of the paper sheets [5,6].
One of the biopolymers used in packaging applications is chitosan—a polysaccharide
that consists of D-glucosamine and N-acetyl-D-glucosamine monomers. It is obtained as a
result of deacetylation of chitin—an ingredient of crustacean shells. Chitosan has gained
much recognition due to its properties such as biodegradability, non-toxicity, filmmaking,
and antimicrobial potential [7].
Bacterial cellulose is a biopolymer obtained from stationary or dynamic bacterial
cultures. One of the most recognized producers belongs to the Komagataeibacter genus
(previously called Acetobacter xylinus or Gluconacetobacter xylinus) [
8
]. Bacterial cellulose is
created at the edge of the liquid–gas phases in the form of hydrogel [
9
]. It is characterized
by significant water retention, the possibility of obtaining different shapes, and good
mechanical properties compared to plant cellulose due to the lack of lignin or hemicellulose
Int. J. Mol. Sci. 2021,22, 7383. https://doi.org/10.3390/ijms22147383 https://www.mdpi.com/journal/ijms
Int. J. Mol. Sci. 2021,22, 7383 2 of 13
in its structure. Moreover, the crystallinity of bacterial cellulose is higher than in plant
cellulose, resulting in good mechanical properties [7].
One of the most promising application areas of bacterial cellulose is the paper and tex-
tile industry, where it can be used as a reinforcing agent in the form of nanocrystals (BCNC)
or nanofibers (BCNF) [
10
]. Bacterial cellulose nanocrystals, also called nanowhiskers, are
characterized by a diameter of 4–25 nm and a length of 100–1000 nm and occur in the shape
of needles. They can also be obtained in the form of nanofibers, which have a length of
around 10–100 nm and are obtained by physical processes such as homogenization, ball
milling, or sonication [11,12].
Moreover, the possibility of incorporating various nanoparticles into different biopoly-
mers provides new opportunities for their application. In addition, nanoparticles, such as
silver, copper, or zinc oxide, are used as one of the components to enhance the antimicrobial
properties of paper packaging. Zinc oxide is widely used in research concerning electronics,
photocatalysis, sensors, construction materials, and medicine [
13
,
14
]. It is considered GRAS
(generally recognized as safe) by the U.S. Food and Drug Administration (FDA) and can
be used as a part of food packaging [
15
,
16
]. Zinc oxide exhibits an efficient antimicrobial
response and is mainly incorporated into the polymer matrix as an additive.
Many studies have utilized the above-mentioned components in the fabrication of
films or paper coatings. Salari et al. [
7
] used BCNC, chitosan, and silver nanoparticles to
fabricate nanocomposites in the form of film. It expressed good barrier and mechanical
properties and exhibited antimicrobial activity. George and Siddaramaiah [
17
] formulated
a composite based on BCNC and gelatin, which resulted in the enhancement of mechanical
properties compared to pristine gelatin film. Moreover, George et al. [
18
] noted higher
thermal stability and better mechanical properties of BCNC-poly(vinyl alcohol) composite
in comparison to the film from the pure polymer. In turn, Viana et al. [
19
] obtained films
based on pectin and bacterial cellulose in the form of BCNF. The films were character-
ized with better mechanical properties and water resistance than pristine pectin films.
Yadav et al. [20]
produced chitosan-based films containing ZnO nanoparticles and gallic
acid that exhibited good antimicrobial and mechanical properties and antioxidant behav-
ior. Some authors prepared coated paper samples. Divsalar et al. [
21
] prepared a paper
coated with chitosan, ZnO, and nisin that showed antibacterial activity. Prasad et al. [
22
]
obtained papers with ZnO and soluble starch. The samples exhibited improved whiteness,
oil absorbency, and excellent antifungal and UV-protecting properties.
To our knowledge, only one research article covered the use of chitosan, bacterial cel-
lulose, and ZnO [
23
]. However, the application and processing of the components differed
from the method applied in this paper. The authors prepared antibacterial dressing by
immersion of oxidized bacterial cellulose hydrogels in chitosan solution and thereafter, syn-
thesized ZnO particles on the surface. Here, we focus on the functionalization of the paper
sheets to provide good antibacterial and mechanical properties; therefore, two well-known
antibacterial components, i.e., chitosan and ZnO particles, were employed. Bacterial cellu-
lose was applied in the form of nanofibers to enhance mechanical properties. In addition,
chitosan is characterized by excellent film-making properties and was applied as the matrix
in which the ZnO-modified bacterial cellulose was incorporated. The proposed method
of fabrication significantly reduces the impact on the environment. The first example is
the use of biopolymers as an alternative to non-degradable ingredients. Secondly, the
concentration of ZnO particles is relatively low to avoid a possible cytotoxic effect, while
the antibacterial potential of the composites is maintained by the use of chitosan. More-
over, bacterial cellulose processing is based on ball milling and sonication instead of acid
hydrolysis, which requires the use of concentrated HCl or H
2
SO
4
. Direct synthesis of ZnO
on the surface of bacterial cellulose fibers reduces the number of performed procedures
and time of experiments.
Here, we focused on the fabrication of paper coating based on chitosan, bacterial
cellulose, and ZnO to induce antimicrobial response and enhance mechanical properties
with respect to pristine paper. The processing of bacterial cellulose sheets was performed
Int. J. Mol. Sci. 2021,22, 7383 3 of 13
via lyophilization, ball milling, sonication, and re-lyophilization. It resulted in the formation
of bacterial cellulose nanofibers (BCNF). These nanostructures were later decorated with
ZnO particles in two different shapes: rods and irregular sphere-like particles. Therefore,
the morphology and their performance when used in paper coatings were efficiently tuned.
2. Results
2.1. Characterization of the Composites and Coatings
SEM analysis allowed the change in bacterial cellulose structure to be observed af-
ter 1-hour sonication. The process resulted in partial separation of the nanofibers. The
comparison of non-sonicated, agglomerated bacterial cellulose and the sonicated sample is
presented in Figure 1. Moreover, SEM enabled the preliminary verification of ZnO synthe-
sis on the bacterial cellulose surface. The micrographs in Figure 2present the modification
of morphology of the nanocomposites affected by different temperatures applied during
metal oxide deposition: room temperature (a) and 80
◦
C (b). Noticeable differences were
observed, such as the size and the shape of the ZnO particles. ZnO synthesized at room
temperature is characterized by nanometric size and non-uniform structure. Moreover,
the particles were agglomerated. However, the shape of ZnO synthesized at 80
◦
C can be
described as elongated rods with a diameter ~200 nm and length 1 µm.
Int. J. Mol. Sci. 2021, 22, x 3 of 14
Here, we focused on the fabrication of paper coating based on chitosan, bacterial
cellulose, and ZnO to induce antimicrobial response and enhance mechanical properties
with respect to pristine paper. The processing of bacterial cellulose sheets was performed
via lyophilization, ball milling, sonication, and re-lyophilization. It resulted in the for-
mation of bacterial cellulose nanofibers (BCNF). These nanostructures were later deco-
rated with ZnO particles in two different shapes: rods and irregular sphere-like particles.
Therefore, the morphology and their performance when used in paper coatings were ef-
ficiently tuned.
2. Results
2.1. Characterization of the Composites and Coatings
SEM analysis allowed the change in bacterial cellulose structure to be observed after
1-hour sonication. The process resulted in partial separation of the nanofibers. The
comparison of non-sonicated, agglomerated bacterial cellulose and the sonicated sample
is presented in Figure 1. Moreover, SEM enabled the preliminary verification of ZnO
synthesis on the bacterial cellulose surface. The micrographs in Figure 2 present the
modification of morphology of the nanocomposites affected by different temperatures
applied during metal oxide deposition: room temperature (a) and 80 °C (b). Noticeable
differences were observed, such as the size and the shape of the ZnO particles. ZnO
synthesized at room temperature is characterized by nanometric size and non-uniform
structure. Moreover, the particles were agglomerated. However, the shape of ZnO syn-
thesized at 80 °C can be described as elongated rods with a diameter ~200 nm and length
1 µm.
Figure 1. SEM micrographs of bacterial cellulose (a) before and (b) after sonication.
Figure 1. SEM micrographs of bacterial cellulose (a) before and (b) after sonication.
Int. J. Mol. Sci. 2021, 22, x 4 of 14
Figure 2. SEM micrographs of bacterial cellulose modified with ZnO (a) at room temperature; (b) at
80 °C.
TEM analysis allowed the successful fabrication of the bacterial cellulose-ZnO
composites to be confirmed and detailed analysis of their morphology. Figure 3 presents
images of all the obtained composites. The BCsonTZnO composite consisted of agglom-
erated ZnO particles in the network of relatively well-separated nanofibers of bacterial
cellulose. On the other hand, the BCson80ZnO composite contained long ZnO rods
placed on the fibers. TEM analysis confirmed that sonication induced the fabrication of
bacterial cellulose nanofibers. Moreover, elemental mapping of the obtained composites
was carried out to assess the location of the elements in the samples. This confirmed the
presence of carbon (C-K), oxygen (O-K), and zinc (Zn-K and Zn-L) (Figure 4).
Figure 3. TEM micrographs of bacterial cellulose-ZnO composites (a) BCsonTZnO; (b)
BCson80ZnO.
Figure 2.
SEM micrographs of bacterial cellulose modified with ZnO (
a
) at room temperature; (
b
) at
80 ◦C.
Int. J. Mol. Sci. 2021,22, 7383 4 of 13
TEM analysis allowed the successful fabrication of the bacterial cellulose-ZnO com-
posites to be confirmed and detailed analysis of their morphology. Figure 3presents images
of all the obtained composites. The BCsonTZnO composite consisted of agglomerated
ZnO particles in the network of relatively well-separated nanofibers of bacterial cellulose.
On the other hand, the BCson80ZnO composite contained long ZnO rods placed on the
fibers. TEM analysis confirmed that sonication induced the fabrication of bacterial cellulose
nanofibers. Moreover, elemental mapping of the obtained composites was carried out to
assess the location of the elements in the samples. This confirmed the presence of carbon
(C-K), oxygen (O-K), and zinc (Zn-K and Zn-L) (Figure 4).
Int. J. Mol. Sci. 2021, 22, x 4 of 14
Figure 2. SEM micrographs of bacterial cellulose modified with ZnO (a) at room temperature; (b) at
80 °C.
TEM analysis allowed the successful fabrication of the bacterial cellulose-ZnO
composites to be confirmed and detailed analysis of their morphology. Figure 3 presents
images of all the obtained composites. The BCsonTZnO composite consisted of agglom-
erated ZnO particles in the network of relatively well-separated nanofibers of bacterial
cellulose. On the other hand, the BCson80ZnO composite contained long ZnO rods
placed on the fibers. TEM analysis confirmed that sonication induced the fabrication of
bacterial cellulose nanofibers. Moreover, elemental mapping of the obtained composites
was carried out to assess the location of the elements in the samples. This confirmed the
presence of carbon (C-K), oxygen (O-K), and zinc (Zn-K and Zn-L) (Figure 4).
Figure 3. TEM micrographs of bacterial cellulose-ZnO composites (a) BCsonTZnO; (b)
BCson80ZnO.
Figure 3.
TEM micrographs of bacterial cellulose-ZnO composites (
a
) BCsonTZnO; (
b
) BCson80ZnO.
Int. J. Mol. Sci. 2021, 22, x 5 of 14
Figure 4. Elemental analysis of BCson80ZnO composite (the red square indicates the analyzed re-
gion of the sample).
Figure 5 presents the X-ray diffraction patterns taken for the bacterial cellulose
composites. The patterns revealed that the obtained samples exhibit a typical crystalline
form of cellulose I. For each sample, major diffraction peaks at 14.6°, 16.7°, and 22.6°
corresponding to the crystallographic planes of (110), (110), and (200), respectively, could
be recognized. However, several additional peaks in all nanocomposite samples can be
observed. Sharp and intense Bragg reflections are positioned at 31.05°, 34.58°, 36.48°,
47.68°, 56.78°, 63.07°, 66.53°, 68.11°, and 69.29°. These reflections are well-matched with
the usually reported signals of ZnO wurtzite hexagonal structure attributed to (100),
(002), (101), (102), (110), (103), (200), (112), and (201), respectively (following standard
PDF card no. 01-079-0207). The obtained XRD pattern of BCsonTZnO displays a few ad-
ditional diffraction peaks in the range of 20–65°. These comparatively weak signals are
assigned to zinc hydroxide, which is an intermediate product during the formation of
ZnO in alkaline solution. Zn(OH)
2
can only be found in the sample prepared at room
temperature.
Figure 4.
Elemental analysis of BCson80ZnO composite (the red square indicates the analyzed region
of the sample).
Int. J. Mol. Sci. 2021,22, 7383 5 of 13
Figure 5presents the X-ray diffraction patterns taken for the bacterial cellulose com-
posites. The patterns revealed that the obtained samples exhibit a typical crystalline form of
cellulose I. For each sample, major diffraction peaks at 14.6
◦
, 16.7
◦
, and 22.6
◦
corresponding
to the crystallographic planes of (110), (110), and (200), respectively, could be recognized.
However, several additional peaks in all nanocomposite samples can be observed. Sharp
and intense Bragg reflections are positioned at 31.05
◦
, 34.58
◦
, 36.48
◦
, 47.68
◦
, 56.78
◦
, 63.07
◦
,
66.53
◦
, 68.11
◦
, and 69.29
◦
. These reflections are well-matched with the usually reported
signals of ZnO wurtzite hexagonal structure attributed to (100), (002), (101), (102), (110),
(103), (200), (112), and (201), respectively (following standard PDF card no. 01-079-0207).
The obtained XRD pattern of BCsonTZnO displays a few additional diffraction peaks in the
range of 20–65
◦
. These comparatively weak signals are assigned to zinc hydroxide, which
is an intermediate product during the formation of ZnO in alkaline solution. Zn(OH)
2
can
only be found in the sample prepared at room temperature.
Int. J. Mol. Sci. 2021, 22, x 6 of 14
Figure 5. XRD analyses of the obtained bacterial cellulose-ZnO. * ZnO, BC—bacterial cellulose, ^
Zn(OH)2 (a.u.–arbitrary unit).
Figure 6 shows FT-IR spectra of two representatives of bacterial cellulose in respect
to the pristine bacterial cellulose sample. All spectra contain the main bands: at 3432 cm−1
attributed to the O-H stretching, 2921 cm−1 and 2853 cm−1 characteristic of C-H stretching
of the CH2 and CH3 groups, 1165 cm−1 assigned to C–O–C antisymmetric bridge
stretching of 1,4-β-d-glucoside and 1053 cm−1 corresponding to bending of the C–O–H
bond of carbohydrate. The band centered around 1626 cm−1 is due to the O-H bending of
adsorbed water. It is present in all samples, and its intensity is the highest for the pure BC
sample, indicating the hydrophilic character of the material. There are some differences
between BC and all obtained composites. Subtle changes can be observed in the
low-wavenumber region, where the bands characteristic of Zn-containing groups have
been observed (400–500 cm−1). The results may be related to the strong chemical interac-
tion between cellulose and ZnO phases. Spectra obtained for the composites show
broadening of the bands in the region 3200–3600 cm−1, probably due to the rearrangement
and increase in the hydroxyl group content. Moreover, the signals in the 2850–2950 cm−1
region have become more distinctive but less intense after the functionalization process.
Figure 5.
XRD analyses of the obtained bacterial cellulose-ZnO. * ZnO, BC—bacterial cellulose,
ˆ Zn(OH)2(a.u.–arbitrary unit).
Figure 6shows FT-IR spectra of two representatives of bacterial cellulose in respect to
the pristine bacterial cellulose sample. All spectra contain the main bands: at
3432 cm−1
attributed to the O-H stretching, 2921 cm
−1
and 2853 cm
−1
characteristic of C-H stretch-
ing of the CH2 and CH3 groups, 1165 cm
−1
assigned to C–O–C antisymmetric bridge
stretching of 1,4-
β
-d-glucoside and 1053 cm
−1
corresponding to bending of the C–O–H
bond of carbohydrate. The band centered around 1626 cm
−1
is due to the O-H bending
of adsorbed water. It is present in all samples, and its intensity is the highest for the
pure BC sample, indicating the hydrophilic character of the material. There are some
differences between BC and all obtained composites. Subtle changes can be observed
in the low-wavenumber region, where the bands characteristic of Zn-containing groups
have been observed (
400–500 cm−1
). The results may be related to the strong chemical
interaction between cellulose and ZnO phases. Spectra obtained for the composites show
broadening of the bands in the region 3200–3600 cm
−1
, probably due to the rearrangement
and increase in the hydroxyl group content. Moreover, the signals in the 2850–2950 cm
−1
region have become more distinctive but less intense after the functionalization process.
Int. J. Mol. Sci. 2021,22, 7383 6 of 13
Int. J. Mol. Sci. 2021, 22, x 7 of 14
Figure 6. FT-IR analyses of the obtained bacterial cellulose-ZnO composites (a.u.–arbitrary unit)
2.2. Antibacterial Properties
The results for antibacterial properties are presented in Figure 7. The antimicrobial
assay showed a 96.36% reduction in E. coli titer after incubation with chitosan-coated
paper and a 100% reduction with both papers coated with fabricated chitosan-bacterial
cellulose-ZnO composites. In the case of pristine paper, the titer of bacteria was increased
by 70%. In this study, it is crucial to point out that there is no shape/size effect of ZnO on
antimicrobial response.
Figure 7. Antibacterial properties assay according to ASTM E2149-13a standard (chitosan—paper
coated with chitosan, ChBCsonTZnO—paper coated with chitosan, sonicated bacterial cellulose
Figure 6. FT-IR analyses of the obtained bacterial cellulose-ZnO composites (a.u.–arbitrary unit).
2.2. Antibacterial Properties
The results for antibacterial properties are presented in Figure 7. The antimicrobial
assay showed a 96.36% reduction in E. coli titer after incubation with chitosan-coated
paper and a 100% reduction with both papers coated with fabricated chitosan-bacterial
cellulose-ZnO composites. In the case of pristine paper, the titer of bacteria was increased
by 70%. In this study, it is crucial to point out that there is no shape/size effect of ZnO on
antimicrobial response.
Int. J. Mol. Sci. 2021, 22, x 7 of 14
Figure 6. FT-IR analyses of the obtained bacterial cellulose-ZnO composites (a.u.–arbitrary unit)
2.2. Antibacterial Properties
The results for antibacterial properties are presented in Figure 7. The antimicrobial
assay showed a 96.36% reduction in E. coli titer after incubation with chitosan-coated
paper and a 100% reduction with both papers coated with fabricated chitosan-bacterial
cellulose-ZnO composites. In the case of pristine paper, the titer of bacteria was increased
by 70%. In this study, it is crucial to point out that there is no shape/size effect of ZnO on
antimicrobial response.
Figure 7. Antibacterial properties assay according to ASTM E2149-13a standard (chitosan—paper
coated with chitosan, ChBCsonTZnO—paper coated with chitosan, sonicated bacterial cellulose
Figure 7.
Antibacterial properties assay according to ASTM E2149-13a standard (chitosan—paper
coated with chitosan, ChBCsonTZnO—paper coated with chitosan, sonicated bacterial cellulose
and ZnO synthesized at the room temperature, ChBCson80ZnO—paper coated with chitosan with
sonicated bacterial cellulose and ZnO synthesized at 80 ◦C).
Int. J. Mol. Sci. 2021,22, 7383 7 of 13
2.3. Mechanical Properties
To verify the effect of the various coatings on the mechanical properties of the non-
coated and coated paper, sheets were subjected to mechanical tests. The tests evaluated
the tensile strength, tearing strength, and bursting strength. For each test, eight different
paper sheet samples were measured and the average values were calculated. The standard
deviation of measured values was also indicated. Because of the slight changes in weight of
the coated paper sheets, all the collected data are presented as a strength index, which is a
preferable factor to compare the samples with different grammages. Table 1summarizes the
obtained results, indicating enhancement of mechanical parameters of the coated samples
in respect to the pristine paper. The tensile strength value of the coated paper sheets was
increased by (on average) ~8.5% as compared to the reference sample. Tearing strength
value was improved (on average) by 14.5% in the machine direction and even more in the
cross-machine direction—18%. The bursting strength value of the coated paper sheets also
increased by 16.5% on average. Interestingly, both composite-coated samples have shown
similar mechanical performance concerning tear index, indicating that the shape of ZnO did
not affect it. However, tensile strength and burst index differed in the samples and sample
ChBCson80ZnO exhibited better mechanical properties than sample ChBCsonTZnO. The
tensile index shows that both samples containing bacterial cellulose and ZnO exhibited
higher values than pristine chitosan and pristine paper. It is also worth underlining that
paper sheets coated with pristine chitosan presented the best tear index (CD) value from all
of the analyzed samples. Conducted research confirms that all coated samples had better
mechanical properties than uncoated paper, which can be mostly assigned to chitosan.
Only the tensile index was significantly improved in the case of composites (in comparison
with chitosan coating and non-coated paper).
Table 1. The effect of the different coatings on the mechanical properties of paper.
Pristine Paper Chitosan ChBCsonTZnO ChBCson80ZnO
Tensile index a b c d
[N m/g] 40.47 ±0.35 43.20 ±0.2 44.12 ±0.21 44.52 ±0.33
Tear index (MD *) a b b b
[mN m2/g] 5.66 ±0.28 6.49 ±0.28 6.44 ±0.21 6.52 ±0.26
Tear index (CD *) a b c c
[mN m2/g] 5.86 ±0.28 7.32 ±0.11 6.69 ±0.36 6.77 ±0.46
Burst index a bc b c
[kPa m2/g] 1.32 ±0.08 1.55 ±0.06 1.48 ±0.04 1.60 ±0.05
* MD: machine direction, * CD: cross direction, values marked with different letters (a, b, c, d) are significantly
different (p< 0.05, ANOVA, Tukey test).
3. Discussion
Our study indicated that fabricated paper coated with composites based on chitosan,
bacterial cellulose, and ZnO exhibited enhanced antibacterial activity and mechanical
performance. The antibacterial effect may be explained by the analysis of the antimicrobial
properties of chitosan and ZnO. In the case of chitosan, its properties are associated with
many factors, e.g., pH of the solution, molecular weight and degree of acetylation, or the
surface of contact with the cells [
24
,
25
]. There are several mechanisms of the antimicrobial
activity of chitosan described in the literature [
26
]: (1) The first one is explained as an
electrostatic attraction of positively charged chitosan and negatively charged components
on the surface of bacterial cells. (2) Another proposed mechanism is based on the ability of
chitosan to penetrate the cell, bind with DNA and disturb the transcription and translation
processes. An effect of such action is the disorganization of protein synthesis crucial for
sustaining cells’ homeostasis. The last (3) mechanism relies on the chelation of metal ions
by amino groups of chitosan. Such effects are observed in pH above six, since amino groups
Int. J. Mol. Sci. 2021,22, 7383 8 of 13
become unprotonated and the pair of electrons are donated to metal. This results in the
creation of metal complexes.
The bactericidal properties of zinc oxide were described by many authors and are
a well-known phenomenon [
27
,
28
]. The antimicrobial activity of zinc oxide nanoparti-
cles is hypothesized to be based on three main mechanisms: (1) the release of Zn
2+
ions,
(2) interaction
of nanoparticles with bacteria, which may result in cell disruption, (3) pro-
duction of reactive oxygen species (ROS) [
29
,
30
]. In the presented research, the size/shape
of the particles was assessed by transmission electron microscopy. The size of ZnO particles
was estimated as nanometric in the case of ZnO synthesized at room temperature, while
ZnO synthesized at 80
◦
C was characterized by micrometric dimensions. On that basis, we
hypothesize that the most probable antimicrobial mechanism of the fabricated coatings
was acting through zinc ions released to the buffer used in the conducted assay. Such a
process is connected to the amphoteric nature of ZnO in water solutions. The ions bind
with the thiol groups of the enzymes involved in cell respiration, which disorganizes their
functions and leads to cell death [
29
,
30
]. Therefore, ZnO particles are frequently used
in the fabrication of antimicrobial films or paper. However, the cytotoxic effect of high
concentrations of ZnO particles was frequently reported in the literature [
31
,
32
]. There-
fore, we decided to apply a relatively small amount of ZnO in the prepared composites
by employing another ingredient—chitosan. Chitosan is also known as an antimicrobial
agent and is recognized as a non-toxic, biodegradable polysaccharide. It is the second
most abundant natural polymer, after plant cellulose [
33
]. Moreover, it exhibits excellent
coating properties and therefore, it played a dual role in the prepared composites—the
film-forming matrix in which ZnO-modified bacterial cellulose is incorporated and the
antimicrobial agent. However, the antimicrobial activity of chitosan is limited and depends
on many factors [
7
,
34
,
35
]. Therefore, two antimicrobial factors were chosen to fabricate
the paper coating to obtain the additive effect. Other published papers employ the same
strategy, i.e., the use of two antimicrobial agents [
23
,
36
]. The assay of antimicrobial activity
of the composites revealed that the combination of chitosan and ZnO was more effective
than chitosan alone and led to a 100% reduction in bacterial titer, while paper coated with
pristine chitosan exhibited a 96.36% reduction.
The benefits of using nanocellulose in the improvement of mechanical properties
have already been addressed in the literature [
37
]. The addition of cellulose nanostruc-
tures having a high surface-to-volume ratio improves the formation of hydrogen bonding
within cellulose pulp, which increases density, boosting the mechanical performance of
paper. Tanpichai et al. [
38
] reported a significant enhancement of mechanical properties
of paper composed of 50 wt% nanofibrillated cellulose (NFC). Tensile strength and strain
were 10-fold and 3-fold higher than those of the paper without NFC, respectively. Jin
and his coworkers [
39
] have designed paper coating using nanofibrillated cellulose as a
coating agent. The results of their studies revealed that increased NFC addition led to the
enhancement of tensile strength, which was achieved as a function of the NFC addition in
the paper coating system. They demonstrated that 0.03% addition of NFC improved the
tensile strength of coated paper by approximately 2.5%.
Recent studies have also found the viability of chitosan as a paper coating not only for
the implementation of antibacterial features but also to improve its mechanical properties.
This enhancement of mechanical properties might be due to the fact that pores within the
paper can be filled with polymer molecules. Zakaria et al. [
40
] have coated A4 paper with
2 wt% of chitosan solution and reported some changes in paper strength and toughness
in comparison to uncoated samples. The burst and tensile strength values for the coated
paper have increased by 9% and 6%, respectively. Moreover, it has been reported that
chitosan adheres well to the fiber surfaces, causing the formation of bridges between
inter-fiber distances [
41
]. Thus, coating paper with a mixture of chitosan and nanocellulose
can benefit from the formation of bonds between cellulose fibers and nanocellulose fibrils.
Therefore, exploiting the additive effect of bacterial cellulose nanofibers and chitosan for
the reinforcement of mechanical properties is possible.
Int. J. Mol. Sci. 2021,22, 7383 9 of 13
It is worth underlining that, in our studies, the improvement of mechanical properties
of the coated paper sheets can mostly be assigned to chitosan. Overall, the ChBCson80ZnO
sample exhibited the best mechanical properties, excluding tear index (CD).
4. Materials and Methods
Zinc acetate dihydrate (Zn(CH3COO)2×2H2O), acetic acid, and medium molecular
weight chitosan (190,000–310,000 Da, 75–85% deacetylated) were purchased from Mili-
poreSigma (Darmstadt, Germany). Sodium hydroxide (NaOH) was supplied by Chempur
(Piekary ´
Sl ˛askie, Poland).
4.1. Bacterial Cellulose Growth, Processing and Functionalization with ZnO
Bacterial cellulose was produced by Komagataeibacter xylinus ATCC
®
53524
™
. The
culture was conducted for seven days at 30
◦
C in S&H 1717 ATCC medium (bactopeptone
5 g/L
, yeast extract 5 g/L, Na
2
HPO
4
2.7 g/L, citric acid 1 hydrate 1.15 g/L). After steril-
ization, the aqueous solution of mannitol (20% w/w) was added at the amount of
20 g/L
,
and the medium was buffered to pH = 5. Based on the literature [
42
], mannitol is one of
the best carbon sources for selected bacteria strains—it results in high BC yield in a short
time and the highest crystallinity index. Next, the inoculum (20 mL) was transferred to
the new portion of the sterile medium and cultivated in a stationary culture (1.2 L) on
polypropylene trays for the next eight days at 30
◦
C. After the incubation time, the sheet of
bacterial cellulose was harvested, rinsed thoroughly with distilled water, and incubated in
0.1 M NaOH solution at 80
◦
C for 30 min to remove the residual cells. After that, the sheet
was rinsed again with distilled water to remove the residue of NaOH.
Bacterial cellulose processing was based on the lyophilization of the whole sheet,
ball milling (1 h), sonication for 1 h, and re-lyophilization. This approach resulted in the
formation of bacterial cellulose nanofibers (BCNF) due to mechanical processing.
The synthesis of the zinc oxide particles was conducted directly on bacterial cellulose
samples according to the modified method by Ali et al. [
43
]. The calculated ratio of the
bacterial cellulose:ZnO was 1:2. Briefly, 750 mg of the bacterial cellulose was inserted into
250 mL of distilled water and stirred with a magnetic stirrer (300 rpm, 30 min) to obtain
homogenous dispersion. Next, Zn(CH
3
COO)
2×
2H
2
O was added to the flask and stirred
for the next 0.5 h. After that, 0.1M NaOH was introduced using a vacuum pump with the
flow 3 mL/minute (Programmable Microfluidics Syringe Pump NE-1002X, Ala Scientific,
Farmingdale, NY, USA). After this step, the obtained pellet was washed with ethanol, and
the residues were rinsed with distilled water and filtered on a Whatman filter (0.2
µ
m)
until pH = 7 was reached. Then, the samples were dried at 60 ◦C.
4.2. Preparation of Chitosan Composites
The chosen concentration of the chitosan solution was 1.5% w/vin 1% v/vwater
solution of the acetic acid based on preliminary attempts to coat a sheet of paper. The
solution was placed on the magnetic stirrer (300 rpm) and sonicated for 15 min until a
homogeneous suspension was obtained. The final composites were prepared by adding
10% w/w(in relation to the dry mass of chitosan) of bacterial cellulose modified with
ZnO into the chitosan solution. The composites were stirred with a magnetic stirrer for
30 min and sonicated (15 min) to obtain homogenous dispersion of the modified bacterial
cellulose particles. The final concentrations of bacterial cellulose and chitosan equaled
6.77% and 3.33%, respectively. Coating of the kraft paper sheets (grammage 90 g/m
2
,
Arctic Paper S.A., Poznan, Poland) was conducted with a coating machine (RK K Control
Coater, Royston, UK) by distribution of the nanocomposite on the surface of the paper
sheet with a squeegee with a coating thickness of 12
µ
m. Afterward, the coated papers
were air-dried. All the samples are listed in Table 2.
Int. J. Mol. Sci. 2021,22, 7383 10 of 13
Table 2. The list of the tested samples.
Sample Abbreviation Description of the Sample
P Non-coated paper
Ch Paper coated with chitosan solution
ChBCsonTZnO Paper coated with chitosan solution with the addition of the
BCNF modified with ZnO synthesized at room temperature
ChBCson80ZnO Paper coated with chitosan solution with the addition of the
BCNF modified with ZnO synthesized at 80 °C
4.3. Characterization
SEM analysis was conducted to assess the morphology of the bacterial cellulose and
obtained ZnO particles. The samples were prepared on carbon tape and sputtered with
chromium. The voltage of the electron beam equaled 20 kV (VEGA3, TESCAN, Brno, Czech
Republic). TEM analysis was carried out to precisely assess the size of the obtained ZnO
particles and the efficiency of the sonication of the bacterial cellulose. The samples were
sonicated and placed on a copper grid and incubated at 60
◦
C to remove the water. The
electron beam voltage used was 200 kV (Tecnai F30, Thermo Fisher Scientific, Waltham, MA,
USA). Additional elemental analysis was run to identify the elements of the composites.
XRD allowed the confirmation of the presence of the bacterial cellulose and ZnO particles
in the samples before insertion into the chitosan solution. The powdered sample was
placed on the rack, and the measurements were conducted in the range of 10–75
◦
, with the
copper lamp as a radiation source (K
α
1 = 1.54056 Å) (Aeris Research, Malvern Panalytical,
Malvern, UK). The FT-IR method (Nicolet 6700 FT-IR, Thermo Fisher Scientific, Waltham,
MA, USA) was used to identify the characteristic groups of the used components. The
samples were prepared by forming tablets with KBr. The measurements were conducted in
the range of 4000–400 cm−1.
4.4. Antibacterial Properties
The assessment of the antimicrobial properties of the coated paper was conducted
according to ASTM E2149-13a standard (Standard Test Method for Determining the An-
timicrobial Activity of Antimicrobial Agents Under Dynamic Contact Conditions). The
bacteria were kept at
−
20
◦
C in a trypticase soy broth (TSB) medium containing 10%
glycerol. Before the study, the microorganisms were revived on trypticase soy agar (TSA)
and incubated at 37
◦
C for 24 h. For experiments, bacteria were inoculated into falcon-type
tubes (50 mL) containing 30 mL of TSB and incubated overnight at 37
◦
C on a rotary shaker
for 18 h. Then, the cultures were diluted in phosphate buffer (0.3 mM KH
2
PO
4
), and the
obtained inoculum was used for the experiments. One gram of each paper sample was
weighed on the analytical balance and inserted into sterile Erlenmeyer flasks. Next, 50 mL
of the inoculum was added, the solution was mixed by hand, and 100
µ
L of each sample
was collected for the plating. All the samples were incubated at room temperature for 1 h
with shaking (150 rpm). Afterward, 100
µ
L of the cultures were collected for plating on
plate count agar (PCA) in two repetitions. The plates were incubated at 37
◦
C for 24 h. After
the incubation, the colonies were counted, and the reduction percentage was calculated in
comparison to the control.
4.5. Mechanical Properties
The mechanical properties of the functionalized and non-functionalized paper samples
were investigated. For comparative purposes, non-coated paper sheets were also tested
and used as a reference sample. The mechanical tests were carried out at the Arctic Paper
company in an air-conditioned room (23
◦
C, 50% of the humidity level). Tearing resistance
was determined using an Elmendorf apparatus (Lorentzen & Wettre, Zurich, Switzerland)
according to ISO 1924-2. The width and length of the tested paper strips were 15 and
100 mm
, accordingly. The tensile strength measurements were conducted on the automatic
Int. J. Mol. Sci. 2021,22, 7383 11 of 13
tensile tester (Messmer Büchel, K465, Veenendaal, The Netherlands), according to ISO 1974
on samples consisting of 4 paper sheets. The bursting strength was tested on the bursting
strength tester (Messmer Büchel, Veenendaal, The Netherlands) according to ISO 2758 on
paper samples with dimensions of more than 70 mm ×70 mm.
5. Conclusions
In summary, paper sheets coated with composites based on chitosan, bacterial cellu-
lose (nanofibers), and ZnO were fabricated. They exhibited enhanced antibacterial and
mechanical properties. The experimental conditions allowed obtaining ZnO in the shape
of rods and irregular sphere-like particles. However, no size/shape effect on antimicrobial
response was detected. The boosting of the mechanical properties has been assigned
mostly to chitosan; however, the tensile index was significantly improved in composites
in comparison to chitosan-coated paper sheets. In addition, excellent antimicrobial ac-
tivity was observed thanks to the co-application of chitosan and ZnO. Overall, the best
antibacterial (100% of bacterial titer reduction) and mechanical properties (excluding tear
index (MD)) were obtained for composites consisting of chitosan, bacterial cellulose and
ZnO synthesized at 80
◦
C. Therefore, we assume that the designed paper coated with
chitosan-bacterial cellulose-ZnO composites may be a promising eco-friendly composition
in food packaging applications.
Author Contributions:
Conceptualization, J.J., M.O. and E.M.; formal analysis, M.K., A.A., R.R. and
E.M.; funding acquisition, R.R. and E.M.; investigation, J.J., M.O., M.K. and A.A.; methodology,
J.J., M.O., M.K., A.A. and E.M.; project administration, R.R. and E.M.; resources, R.R. and E.M.;
supervision, R.R. and E.M.; visualization, J.J. and M.O.; writing—original draft, J.J., M.O., M.K., A.A.,
R.R. and E.M.; writing—review and editing, J.J., M.O., M.K., A.A., R.R. and E.M. All authors have
read and agreed to the published version of the manuscript.
Funding:
This research was funded by the National Centre for Research and Development, grant
number POWR.03.05.00-00-Z205/17.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Acknowledgments:
The authors are grateful for the financial support of the National Centre for
Research and Development within the POWER Program (Grant No. POWR.03.05.00-00-Z205/17).
The obtained research was carried out in the Fabrication Laboratory (Fab-LAB) supported by the
National Centre for Research and Development. Adrian Augustyniak was supported by the German
Research Foundation (DFG) as part of the Research Training Group on Urban Water Interfaces
(GRK 2032).
Conflicts of Interest: Authors declare that they have no conflict of interest.
References
1.
Kumar, N.; Kaur, P.; Bhatia, S. Advances in bio-nanocomposite materials for food packaging: A review. Nutr. Food Sci.
2017
,47,
591–606. [CrossRef]
2.
Molina-Besch, K.; Wikström, F.; Williams, H. The environmental impact of packaging in food supply chains—does life cycle
assessment of food provide the full picture? Int. J. Life Cycle Assess. 2019,24, 37–50. [CrossRef]
3.
Bala, A.; Laso, J.; Abejón, R.; Margallo, M.; Fullana-i-Palmer, P.; Aldaco, R. Environmental assessment of the food packaging waste
management system in Spain: Understanding the present to improve the future. Sci. Total Environ.
2020
,702, 134603. [CrossRef]
4.
Ncube, L.K.; Ude, A.U.; Ogunmuyiwa, E.N.; Zulkifli, R.; Beas, I.N. Environmental impact of food packaging materials: A review
of contemporary development from conventional plastics to polylactic acid based materials. Materials
2020
,13, 4994. [CrossRef]
[PubMed]
5.
Gruji´c, R.; Vujadinovi´c, D.; Savanovi´c, D. Biopolymers as food packaging materials. In Advances in Applications of Industrial
Biomaterials; Pellicer, E., Nikolic, D., Sort, J., Baró, M., Zivic, F., Grujovic, N., Grujic, R., Pelemis, S., Eds.; Springer International
Publishing: Cham, Switzerland, 2017; pp. 139–160. ISBN 978-3-319-62767-0.
6.
Porta, R.; Sabbah, M.; Di Pierro, P. Biopolymers as food packaging materials. Int. J. Mol. Sci.
2020
,21, 4942. [CrossRef] [PubMed]
Int. J. Mol. Sci. 2021,22, 7383 12 of 13
7.
Salari, M.; Sowti Khiabani, M.; Rezaei Mokarram, R.; Ghanbarzadeh, B.; Samadi Kafil, H. Development and evaluation of chitosan
based active nanocomposite films containing bacterial cellulose nanocrystals and silver nanoparticles. Food Hydrocoll.
2018
,84,
414–423. [CrossRef]
8.
Gorgieva, S.; Trˇcek, J. Bacterial cellulose: Production, modification and perspectives in biomedical applications. Nanomaterials
2019,9, 1352. [CrossRef] [PubMed]
9.
Ol˛edzki, R.; Walaszczyk, E. Bionanocellulose—Properties, acquisition and perspectives of application in the food industry. Post˛epy
Mikrobiol. Adv. Microbiol. 2020,59, 87–102. [CrossRef]
10.
Rahimi Kord Sofla, M.; Brown, R.J.; Tsuzuki, T.; Rainey, T.J. A comparison of cellulose nanocrystals and cellulose nanofibres
extracted from bagasse using acid and ball milling methods. Adv. Nat. Sci. Nanosci. Nanotechnol. 2016,7. [CrossRef]
11.
Azeredo, H.M.C.; Rosa, M.F.; Mattoso, L.H.C. Nanocellulose in bio-based food packaging applications. Ind. Crop. Prod.
2017
,97,
664–671. [CrossRef]
12.
Abral, H.; Lawrensius, V.; Handayani, D.; Sugiarti, E. Preparation of nano-sized particles from bacterial cellulose using ultrasoni-
cation and their characterization. Carbohydr. Polym. 2018,191, 161–167. [CrossRef]
13. Sikora, P.; Augustyniak, A.; Cendrowski, K.; Nawrotek, P.; Mijowska, E. Antimicrobial activity of Al2O3, CuO, Fe3O4, and ZnO
nanoparticles in scope of their further application in cement-based building materials. Nanomaterials 2018,8, 212. [CrossRef]
14.
Augustyniak, A.; Jablonska, J.; Cendrowski, K.; Głowacka, A.; Stephan, D.; Mijowska, E.; Sikora, P. Investigating the release of
ZnO nanoparticles from cement mortars on microbiological models. Appl. Nanosci. 2021. [CrossRef]
15. Pal, M. Nanotechnology: A new approach in food packaging. J. Food Microbiol. Saf. Hyg. 2017,2, 8–9. [CrossRef]
16.
Kim, I.; Viswanathan, K.; Kasi, G.; Thanakkasaranee, S.; Sadeghi, K.; Seo, J. ZnO Nanostructures in active antibacterial food
packaging: Preparation methods, antimicrobial mechanisms, safety issues, future prospects, and challenges. Food Rev. Int.
2020
,
1–29. [CrossRef]
17.
George, J.; Siddaramaiah. High performance edible nanocomposite films containing bacterial cellulose nanocrystals. Carbohydr.
Polym. 2012,87, 2031–2037. [CrossRef]
18.
George, J.; Ramana, K.V.; Bawa, A.S.; Siddaramaiah. Bacterial cellulose nanocrystals exhibiting high thermal stability and their
polymer nanocomposites. Int. J. Biol. Macromol. 2011,48, 50–57. [CrossRef]
19.
Viana, R.M.; Sá, N.M.S.M.; Barros, M.O.; Borges, M.d.F.; Azeredo, H.M.C. Nanofibrillated bacterial cellulose and pectin edible
films added with fruit purees. Carbohydr. Polym. 2018,196, 27–32. [CrossRef] [PubMed]
20.
Yadav, S.; Mehrotra, G.K.; Dutta, P.K. Chitosan based ZnO nanoparticles loaded gallic-acid films for active food packaging. Food
Chem. 2021,334, 127605. [CrossRef] [PubMed]
21.
Divsalar, E.; Tajik, H.; Moradi, M.; Forough, M.; Lotfi, M.; Kuswandi, B. Characterization of cellulosic paper coated with
chitosan-zinc oxide nanocomposite containing nisin and its application in packaging of UF cheese. Int. J. Biol. Macromol.
2018
,
109, 1311–1318. [CrossRef] [PubMed]
22.
Prasad, V.; Shaikh, A.J.; Kathe, A.A.; Bisoyi, D.K.; Verma, A.K.; Vigneshwaran, N. Functional behaviour of paper coated with zinc
oxide-soluble starch nanocomposites. J. Mater. Process. Technol. 2010,210, 1962–1967. [CrossRef]
23.
Kai, J.; Xuesong, Z. Preparation, characterization, and cytotoxicity evaluation of zinc oxide–bacterial cellulose–chitosan hydrogels
for antibacterial dressing. Macromol. Chem. Phys. 2020,221, 2000257. [CrossRef]
24.
Yilmaz Atay, H. Antibacterial activity of chitosan-based systems. In Functional Chitosan: Drug Delivery and Biomedical Applications;
Jana, S., Jana, S., Eds.; Springer Singapore: Singapore, 2019; pp. 457–489. ISBN 978-981-15-0263-7.
25.
Ke, C.L.; Deng, F.S.; Chuang, C.Y.; Lin, C.H. Antimicrobial actions and applications of chitosan. Polymers
2021
,13, 904. [CrossRef]
[PubMed]
26.
Sahariah, P.; Másson, M. Antimicrobial chitosan and chitosan derivatives: A review of the structure-activity relationship.
Biomacromolecules 2017,18, 3846–3868. [CrossRef] [PubMed]
27.
Gudkov, S.V.; Burmistrov, D.E.; Serov, D.A.; Rebezov, M.B.; Semenova, A.A.; Lisitsyn, A.B. A mini review of antibacterial
properties of ZnO nanoparticles. Front. Phys. 2021,9, 49. [CrossRef]
28.
Tiwari, V.; Mishra, N.; Gadani, K.; Solanki, P.S.; Shah, N.A.; Tiwari, M. Mechanism of antibacterial activity of zinc oxide
nanoparticle against carbapenem-resistant Acinetobacter baumannii.Front. Microbiol. 2018,9, 1218. [CrossRef]
29.
Mishra, P.K.; Mishra, H.; Ekielski, A.; Talegaonkar, S.; Vaidya, B. Zinc oxide nanoparticles: A promising nanomaterial for
biomedical applications. Drug Discov. Today 2017,22, 1825–1834. [CrossRef] [PubMed]
30.
Siddiqi, K.S.; ur Rahman, A.; Tajuddin; Husen, A. Properties of zinc oxide nanoparticles and their activity against microbes.
Nanoscale Res. Lett. 2018,13, 141. [CrossRef] [PubMed]
31.
Ng, C.T.; Yong, L.Q.; Hande, M.P.; Ong, C.N.; Yu, L.E.; Bay, B.H.; Baeg, G.H. Zinc oxide nanoparticles exhibit cytotoxicity and
genotoxicity through oxidative stress responses in human lung fibroblasts and Drosophila melanogaster.Int. J. Nanomed.
2017
,12,
1621–1637. [CrossRef] [PubMed]
32.
Singh, S. Zinc oxide nanoparticles impacts: Cytotoxicity, genotoxicity, developmental toxicity, and neurotoxicity. Toxicol. Mech.
Methods 2019,29, 300–311. [CrossRef]
33.
Kumar, S.; Ye, F.; Mazinani, B.; Dobretsov, S.; Dutta, J. Chitosan nanocomposite coatings containing chemically resistant ZnO–SnOx
core–shell nanoparticles for photocatalytic antifouling. Int. J. Mol. Sci. 2021,22, 4513. [CrossRef]
Int. J. Mol. Sci. 2021,22, 7383 13 of 13
34.
Rodrigues, C.; de Mello, J.M.M.; Dalcanton, F.; Macuvele, D.L.P.; Padoin, N.; Fiori, M.A.; Soares, C.; Riella, H.G. Mechanical,
thermal and antimicrobial properties of chitosan-based-nanocomposite with potential applications for food packaging. J. Polym.
Environ. 2020,28, 1216–1236. [CrossRef]
35.
Zhang, X.; Zhang, Z.; Wu, W.; Yang, J.; Yang, Q. Preparation and characterization of chitosan/Nano-ZnO composite film with
antimicrobial activity. Bioprocess. Biosyst. Eng. 2021,44, 1193–1199. [CrossRef] [PubMed]
36.
Mocanu, A.; Isopencu, G.; Busuioc, C.; Popa, O.M.; Dietrich, P.; Socaciu-Siebert, L. Bacterial cellulose films with ZnO nanoparticles
and propolis extracts: Synergistic antimicrobial effect. Sci. Rep. 2019,9, 17687. [CrossRef]
37.
Fischer, W.J.; Mayr, M.; Spirk, S.; Reishofer, D.; Jagiello, L.A.; Schmiedt, R.; Colson, J.; Zankel, A.; Bauer, W. Pulp fines-
characterization, sheet formation, and comparison to microfibrillated cellulose. Polymers (Basel) 2017,9, 366. [CrossRef]
38.
Tanpichai, S.; Witayakran, S.; Srimarut, Y.; Woraprayote, W.; Malila, Y. Porosity, density and mechanical properties of the paper of
steam exploded bamboo microfibers controlled by nanofibrillated cellulose. J. Mater. Res. Technol.
2019
,8, 3612–3622. [CrossRef]
39.
Jin, K.; Tang, Y.; Liu, J.; Wang, J.; Ye, C. Nanofibrillated cellulose as coating agent for food packaging paper. Int. J. Biol. Macromol.
2021,168, 331–338. [CrossRef] [PubMed]
40.
Zakaria, S.; Chia, C.H.; Wan Ahmad, W.H.; Kaco, H.; Chook, S.W.; Chan, C.H. Mechanical and antibacterial properties of paper
coated with chitosan. Sains Malays. 2015,44, 905–911. [CrossRef]
41.
Rahman Bhuiyan, M.A.; Hossain, M.A.; Zakaria, M.; Islam, M.N.; Zulhash Uddin, M. Chitosan coated cotton fiber: Physical and
antimicrobial properties for apparel use. J. Polym. Environ. 2017,25, 334–342. [CrossRef]
42.
Mikkelsen, D.; Flanagan, B.M.; Dykes, G.A.; Gidley, M.J. Influence of different carbon sources on bacterial cellulose production by
Gluconacetobacter xylinus strain ATCC 53524. J. Appl. Microbiol. 2009,107, 576–583. [CrossRef]
43.
Ali, A.; Ambreen, S.; Maqbool, Q.; Naz, S.; Shams, M.F.; Ahmad, M.; Phull, A.R.; Zia, M. Zinc impregnated cellulose nanocompos-
ites: Synthesis, characterization and applications. J. Phys. Chem. Solids 2016,98, 174–182. [CrossRef]
