The as freeze dried bacterial cellulose and poly vinyl alcohol hydrogel composite was investigated of swelling behavior and gel fraction.. In this study, the gravimetric technique was em[r]
Trang 1Original Article
Dried-state bacterial cellulose (Acetobacter xylinum) and
polyvinyl-alcohol-based hydrogel: An approach to a personal care material
a Materials and Textile Technology, Faculty of Science and Technology, Thammasat University, Patumtani, Thailand
b Laboratory of Organic Synthesis, Chulabhorn Research Institute, Bangkok, Thailand
a r t i c l e i n f o
Article history:
Received 1 May 2018
Received in revised form
15 June 2018
Accepted 23 June 2018
Available online 28 June 2018
Keywords:
Bacterial cellulose
Freeze dried hydrogel
Poly vinyl alcohol
a b s t r a c t Freeze-dried bacterial cellulose and polyvinyl alcohol were successfully prepared The weight ratios of polyvinyl alcohol to bacterial cellulose were set at 3:1, 5:1 and 10:1 With bacterial cellulose present in the polyvinyl alcohol matrix, H-bonds formed along the cross-linked hydrogel network The freeze-dried hydrogel presented good compatibility The hydrogel was thermally stable up to 200 C Scanning electron microscopy showed that the hydrogel presented an interconnected network containing various pore sizes Preliminary experiments on the swelling behavior of the hydrogel were done in DI water, an NaCl solution and a PBS solution The hydrogel showed good swelling characteristics within 30 min Importantly, the freeze-dried hydrogel is an excellent candidate for pharmaceutical and cosmetic materials
© 2018 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
1 Introduction
In recent years, hydrogel has been extremely developed for
significant interest in biomedical fields Utilization of hydrogel
based materials has gained much attraction because of their
distinctive properties and benefit of exhibiting the characteristics
similar to soft biological tissues[1] Due to the viscoelastic
prop-erties and high water content, the hydrogel was employed in
various medical researches, such as bone and cartilage repair, drug
delivery system, and cosmetics, as well as contact lens From the
fundamental point of view, hydrogel can be divided into chemical
gels and physical gels It can be defined that physical gel was formed
by molecular self-assembly through ionic or hydrogen bond, while
chemical gel was formed by covalent bond[2] Up to the present
time, numerous polymers have been extensively investigated of the
feasibility to become hydrogel One of the most interests was
focused on poly(vinyl alcohol) It was considered as a well-known
synthetic polymer ascribed to its desirable characteristics, such as
water-soluble, nontoxic, transparent and biocompatible properties
Our research group has successfully developed poly(vinyl alcohol)
for the drug delivery system [3,4] It was found that poly(vinyl
alcohol) presented the excellent properties such as its chemical
stability and water-uptake capability Moreover, we have extended the scope of work for the gelatin based composite, and found that the utilization of the gelatin based hydrogel also provided good benefits such as cost effectiveness and degradability[5]
However, the use of only neat poly(vinyl alcohol) was still problematic It affected on cell affinity and consequently caused the rejection due to weak adhesion To solve this issue, the design of poly(vinyl alcohol) based composite was considered as an alter-native technique To design such a composite, bacterial cellulose was used as an effective reinforcement From the structural point of view, it was composed of nano-sizedfibril network It was free from wax, lignin and hemicellulose Moreover, it possessed high tensile strength, low co-efficiency of thermal expansion, and high chemi-cal stability The bacterial cellulose was therefore considered as a filler to design the polymer based composites[6e8]
In an attempt to increase the properties of poly(vinyl alcohol) based composites for hydrogel, many scientists found that the bacterial cellulose can be used as a reinforcement material for poly(vinyl alcohol) based hydrogel Wang et al.[9]investigated the preparation and the in vitro characteristics of a bacterial cellulose and poly(vinyl alcohol) hydrogel composite Gao et al.[10]showed that the presence of bacterial cellulose in a hydrogel network had
an effect on the mechanical and rheological properties of the ma-terial This effect was related to the numerical prediction [11] Furthermore, Wang et al.[12]showed the effect of cellulose in the hydrogel network on the self-healing and antibacterial properties
* Corresponding author Fax: þ66 25644458.
E-mail address: sarute.ummartyotin@gmail.com (S Ummartyotin).
Peer review under responsibility of Vietnam National University, Hanoi.
Contents lists available atScienceDirect Journal of Science: Advanced Materials and Devices
j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d
https://doi.org/10.1016/j.jsamd.2018.06.004
2468-2179/© 2018 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license
Journal of Science: Advanced Materials and Devices 3 (2018) 296e302
Trang 2Although the bacterial cellulose and poly(vinyl alcohol) based
composites presented many advantages such as enhanced
me-chanical properties and thermal stability, they were still limited for
the service lifetime of product Water in 3D network of hydrogel
can cause a media for fungal and microbial specie As a
conse-quence, the utilization of hydrogel was limited In order to use
poly(vinyl alcohol) based hydrogel with higher efficiency,
freeze-dried hydrogel was considered as one of the most effective routes
for utilization In 2016, Butylina et al.[13]investigated the
prop-erties of as-prepared and freeze-dried hydrogel made from
poly(-vinyl alcohol) and cellulose With pouring water to freeze-dried
hydrogel, it was swelled and ready to use The utilization of the
dried-state of hydrogel prepared from bacterial cellulose and poly
vinyl alcohol can provide many benefits including lightweight,
packaging design as well as storage One of the most important
applications is focused on personal care cosmetics and treatment
The use of the dried hydrogel has extensively been attractive for
personal care materials, such as cleansing masks and moisturizer
Future application may extend to skincare products, which are
daily employed
In this work, we investigated the physico-chemical properties of
freeze-dried hydrogel prepared from poly(vinyl alcohol) and
bac-terial cellulose based composites Morphological, thermal, and
structural properties of the freeze-dried hydrogel composites were
presented The swelling behavior of the composite was also
studied
2 Experimental
2.1 Materials
Bacterial cellulose was successfully extracted from Nata de coco
product (Chaokoh coconut gel in syrup, Ampol Food Processing
Ltd., Nakornpathom, Thailand) An indigenous dessert of which
main component was reported as bacterial cellulose
Character-izations of bacterial cellulose extracted from Nata de coco were
carried out in our previous work; its characteristics matched those
of bacterial cellulose extracted from the culture of Acetobacter
Xylinum [6e8] On the other hand, poly(vinyl alcohol), sodium
hydroxide were purchased from Ajax Fine-chem, Co LTD Thailand
The average of the molecular weight was estimated to be 10,000 g/
mol Disodium tetraborate with a molecular weight of 381.37 g/
mole was also purchased from Ajax Fine-Chem Co LTD Thailand All
chemical reagents were used as received without further
purification
2.2 Methods
2.2.1 Bacterial cellulose extraction and purification
Bacterial cellulose was extracted from nata de coco, which was
rinsed with distilled water to remove excess sugar and blended in a
laboratory blender to obtain nata de coco pellicles These pellicles
were treated with 0.1 M NaOH at 80C for 2 h to remove any
remaining microorganisms, medium components, and soluble
polysaccharides The purified bacterial cellulose was then
thor-oughly washed with distilled water until a neutral pH was
achieved
2.2.2 Preparation of freeze-dried bacterial cellulose and poly (vinyl
alcohol) composite
Bacterial cellulose and poly (vinyl alcohol) based composite was
prepared as hydrogel form and freeze-dried powder To achieve
this, poly (vinyl alcohol) was completely dissolved in water, and
then a bacterial cellulose suspension was poured into the poly
(vinyl alcohol) solution Borax was employed as a crosslinking
agent The reaction was performed at 70C for 3 h The chemical reaction that occurred between the bacterial cellulose and poly (vinyl alcohol), with 10 wt% of disodium tetraborate, is illustrated in Fig 1 Subsequently, the hydrogel composite was washed with deionized water to remove any unreacted chemicals and stored at
4C In this experiment, neat poly (vinyl alcohol) was also studied for comparison The ratios of the poly (vinyl alcohol) and bacterial cellulose were set as 3:1, 5:1 and 10:1, respectively
To prepare freeze-dried poly (vinyl alcohol) and bacterial cel-lulose composite, the as-prepared hydrogel composite was under-gone a freeze-dry process Drying was performed for 7 hours at a temperature of80C in vacuum of 0.12 mbar After the freeze-dry
process, the sample was kept in a desiccator in order to prevent the moisture adsorption
2.2.3 Investigation of swelling behavior of freeze-dried bacterial cellulose and poly vinyl alcohol based hydrogel composite The as freeze dried bacterial cellulose and poly vinyl alcohol hydrogel composite was investigated of swelling behavior and gel fraction In this study, the gravimetric technique was employed to determine the swelling and equilibrium data of the hydrogel It was immersed in DI water, 0.1 NaCl solution and PBS solution for 3 h After an appropriate time interval, the specimens were removed from the solution, dried with afilter paper to remove excess sol-vent, and were measured Five samples were investigated, and the data were reported as the statistical average and standard devia-tion The swelling ratio was determined as follows (Eq.(1)):
where Wwetis the weight of a swollen hydrogel at a submersion time, and Wdryis the initial weight of the dry hydrogel
2.3 Instruments 2.3.1 Thermogravimetric analysis The thermal degradation behavior of the freeze-dried hydrogel composite was characterized using TGA (TGA Q500, TA In-struments) In total, 20 mg of the sample was heated from room temperature to 700C in N2at a heating rate and aflow rate of 5C/
min and 70 ml/min, respectively
2.3.2 Scanning electron microscopy The freeze dried hydrogel composite was investigated using SEM (SEM, Quanta 250 microscope, Japan) The specimens were gold-coated using a sputtering device (Jeol, JFC-1200) prior to the SEM observation A magnification of 1000 was used
2.3.3 Fourier transform infrared spectroscopy FTIR spectra were recorded using a Fourier transform infrared spectrometer (PerkinElmer, USA) Spectra were measured at room temperature in the spectral range from 4000 to 400 cm1with a resolution of±4 cm1and a scan frequency of 32 times
2.3.4 X-ray diffraction The crystal structure of the freeze dried hydrogel composite was investigated by X-ray diffraction (XRD, Phillips P.W 1830 diffrac-tometer), which was employed using nickel-filtered CuKa radiation The diffraction patterns were recorded over a range of 10e80.
2.3.5 Differential scanning calorimetry DSC of the freeze dried hydrogel composite was performed from room temperature to 400C at a heating rate of 10C/min with a TA-10000 DSC (TA Instruments, DE, USA) The aluminum pan was
N Chunshom et al / Journal of Science: Advanced Materials and Devices 3 (2018) 296e302 297
Trang 3used for the sample holder The glass transition temperature,
melting temperature, and specific heat capacity were determined
from the heatflow curve
3 Results and discussion
3.1 Physico-chemical properties of the freeze-dried hydrogel
composites
Fig 2presents FTIR spectra of the freeze-dried hydrogel
com-posite The characteristic absorption bands at 1100 cm1 and
1750 cm1were attributed to CeO stretching and C]O stretching,
respectively It was referred to poly vinyl alcohol With the
exis-tence of bacterial cellulose, the characteristic cellulose signals of
CeOeC pyranose ring skeletal vibration at 1050 cm1 was
observed This was similar to that reported by Lin et al.[14] It can
be implied that the characteristic peak of poly vinyl alcohol was slightly shifted toward that of cellulose in the composite samples The characteristic peak at 2900 cm1 was attributed to CeH stretching of both bacterial cellulose and poly vinyl alcohol The
OeH stretching was due to the hydrophilic surface
Fig 3shows the crystal structure of the freeze-dried hydrogel composites Without the water, it was important to note that XRD patterns exhibited a crystalline peak at 2q¼ 23corresponding to
the (200) crystal plane, which was coincided with the result re-ported by Yan et al.[15] When bacterial cellulose has been inserted into the freeze-dried poly vinyl alcohol based composite, the in-tensity of the bacterial cellulose peak became stronger It can be suggested that the relative degree of crystallinity of the freeze-dried hydrogel composite was significantly increased The role of
Fig 1 Schematic diagram of as freeze dried poly(vinyl alcohol) and bacterial cellulose hydrogel composite preparation.
N Chunshom et al / Journal of Science: Advanced Materials and Devices 3 (2018) 296e302 298
Trang 4bacterial cellulose in the freeze-dried hydrogel composite was to
provide the good mechanical and thermal properties The
amor-phous region of polyvinyl alcohol was reduced due to the addition
of bacterial cellulose It can be implied that there is an occurrence
reaction between polyvinyl alcohol and bacterial cellulose
Fig 4exhibits the thermal decomposition of the freeze-dried
hydrogel composite Neat polyvinyl alcohol was provided for
com-parison Thermal decomposition of the freeze-dried hydrogel can be
categorized into three different regions From room temperature to
250C, the thermal decomposition was involved in water
evapora-tion approximately 10 %wt of weight loss was observed, suggesting
that the weight loss was ascribed to the loss of free and bound water
It was important to note that freeze-dried hydrogel was easy to
adsorb moisture This is consistent with what was discussed by Qi
et al [16] After that, with the increment on temperature to
250e500C, the weight loss was attributed to decomposition of
polyvinyl alcohol and bacterial cellulose The decomposition curve of
the neat polyvinyl alcohol was shifted toward a slightly higher
temperature This also indicated that with the existence of bacterial cellulose, the composite presented higher thermal stability as also suggested by Saba et al [17] Bacterial cellulose has high melting temperature and it consequently provided high thermal stability for the composite It was notable that both the polyvinyl alcohol and composite exhibited two steps of degradation In the temperature region of 300e400C, the weight loss was due to the elimination of
the residual water trapped in the polyvinyl alcohol and bacterial cellulose Within the temperature region of 400e500 C, it was
involved in the decomposition of both polyvinyl alcohol and bacte-rial cellulose They changed to CO2.The evaporation of water and CO2 has been observed as pathway of the evaporation It presented as a porous structure With the temperature above 500C, the decom-position was terminated 10e20 %wt of yield was observed as a re-sidual It can be also implied that with the existence of bacterial cellulose, higher percent yield of residual was observed, suggesting that bacterial cellulose provided higher thermal stability to the composite From the TGA curves, it can be concluded that there is
no change in thermal stability on the utilization of the freeze-dried hydrogel at room temperature
Fig 5 exhibits the DSC curves of the freeze-dried hydrogel composites It was important to note that the glass transition temperature of neat polyvinyl alcohol was estimated to be 70C, which was very much close to the reported value (about 68 C) [18] With the existence of bacterial cellulose, the glass transition temperature of the polyvinyl alcohol based composite was slightly shifted to a higher value It can be implied that strong interaction between bacterial cellulose and polyvinyl alcohol occurred as suggested by Jipa et al.[19] In addition, the melting temperature
of the freeze-dried hydrogel composite was investigated The endothermic peak was estimated to be 320C This temperature can be used to explain conformational changes within the polymer network It may involve the size of the crystallites and the degree
of crystallinity as suggested by Hassan et al.[20] It was remarkable
to note that as compared with neat poly vinyl alcohol; the melting point of the composite was slightly higher It could be attributed to the dissociation process of inter- and intra-hydrogen bonding
Fig 3 XRD patterns of the freeze-dried hydrogel composites with various PVA to BC
ratios.
N Chunshom et al / Journal of Science: Advanced Materials and Devices 3 (2018) 296e302 299
Trang 5between bacterial cellulose and polyvinyl alcohol The increment
on the melting temperature of the composite indicated that the
incorporation of bacterial cellulose weakened the interaction
be-tween poly vinyl alcohol chain and hindered the crystallization of
poly vinyl alcohol This discussion was fully supported by the XRD
data and analysis
Fig 6 depicts the SEM images revealing the morphological properties of the freeze-dried bacterial cellulose and poly vinyl alcohol based hydrogel composites It was important to note that the hydrogel based composite exhibited an interconnected porous structure with a regular pore distribution The average pore size declined with increment on poly vinyl alcohol content The pore
Fig 5 DSC thermograms of the freeze-dried hydrogel composites.
Fig 6 SEM micrographs of the freeze-dried hydrogel composites: (A) neat poly vinyl alcohol, (B) 3:1 ratio of poly vinyl alcohol and bacterial cellulose, (C) 5:1 ratio of poly vinyl
N Chunshom et al / Journal of Science: Advanced Materials and Devices 3 (2018) 296e302 300
Trang 6size was therefore ranging from 10mm to 100 nm Various pore
sizes provided a better explanation for the swelling capacity and
water evaporation characteristics of the freeze-dried hydrogel
composites With the existence of bacterial cellulose, the physical
crosslinking density of the hydrogel composite increased, causing
the water content in the hydrogel composite to decrease
How-ever, from the fundamental point of view, in a freeze dry process,
free water was frozen into larger ice crystals which were
eventually represented by larger pores This discussion was in
agreement with that of Dinu et al [21] These results are
considered an important relationship in tuning of the size
dis-tribution, which can facilitate permeation of cellular growth
factors when the freeze-dried hydrogel composite is employed as
a medical material
3.2 Swelling properties of the freeze-dried hydrogel composites Fig 7 presents the swelling behavior of the as freeze-dried bacterial cellulose and poly vinyl alcohol based hydrogel com-posites The experiment was set up based on swelling behavior on
DI water, 0.1 NaCl solution and PBS solution, respectively From the fundamental point of view, lesser cross-linked hydrogel exhibited higher water uptake ability, due to the highly cross-linked structure that could not sustain much water within a hydrogel structure In our experiment, the neat poly vinyl alcohol was provided for comparison It was remarkable that poly vinyl alcohol was easy to dissolve in three different media With the existence of bacterial cellulose, the swelling behavior of the as freeze dried hydrogel was determined This phenomenon was attributed to the hydrophilic nature of bacterial cellulose and poly vinyl alcohol[22] However, with the increment on the fraction of bacterial cellulose, the decrease on the swelling behavior of the as freeze dried hydrogel probably occurred due to the reinforcing effect of the bacterial cellulose It was considered as a nano-reinforcing element in the poly vinyl alcohol matrix, restraining the swelling mechanically, resulting in a decrease of water and solvent adsorption at higher bacterial cellulose addition levels This discussion was fully consistent with that of Naizi et al.[23] Compared to different solutions, the swelling behaviors of the as freeze dried bacterial cellulose and poly vinyl alcohol hydrogel were lesser This was due to less amount of free ion in the solu-tions The hypothesis of swelling behavior in different solutions was set up based on ionic strength of the medium that had a vital
influence on the swelling capabilities of the as freeze dried bac-terial cellulose and poly vinyl alcohol hydrogel It may involve in interaction either through surface adsorption or hydrogen bonding between bacterial cellulose and poly vinyl alcohol as suggested by Mandal et al.[24] It was important to note that only
in DI water, the swelling behavior was significantly less DI water
is in neutral pH and there is no ion to adhere on the functional group of bacterial cellulose and poly vinyl alcohol based hydrogel Compared to 0.1 NaCl and PBS solution, there were positive and negative free ions in the solutions, they were consequently dis-solved and adhered on the functional group of bacterial cellulose and poly vinyl alcohol based hydrogel Higher swelling ratios were therefore observed
4 Conclusion The physico-chemical properties of the as-freeze dried bac-terial cellulose and poly vinyl alcohol composites were investi-gated It was found that the properties of the as-freeze dried hydrogel could be modified by adding bacterial cellulose into the poly vinyl alcohol network The 3:1 ratio of the poly vinyl alcohol and bacterial cellulose presented the outstanding swelling behavior The freeze dry technique was used to remove water from hydrogel network It resulted in shrinkage of the hydrogel composite The presence of bacterial cellulose had an important effect on pore size as observed by scanning electron microscope The high amount of bacterial cellulose in the hydrogel composite could form the interaction between poly vinyl alcohol networks, suggesting that the high gel fraction could be obtained No obvious change in the crystallinity of hydrogel was found after the addition of bacterial cellulose For potential biomedical applications of hydrogel, it presented the excellent characteristic in high water absorption The utilization
of the freeze-dried hydrogel can be beneficial for the design and point of care product for patients It should be further employed and developed for pharmaceutical technology and cosmetic products
Fig 7 Swelling behaviors of (A) DI water, (B) 0.1 M NaCl solution, (C) PBS solution of
N Chunshom et al / Journal of Science: Advanced Materials and Devices 3 (2018) 296e302 301
Trang 7The authors would like to acknowledge thefinancial support
provided by Thammasat University (2018) We are grateful for the
space and research facilities supported by the Chulabhorn Research
Institute Special thank was extended to Plastic Institute of
Thailand
References
[1] K Varaprasad, et al., A mini review on hydrogels classification and recent
developments in miscellaneous applications, Mater Sci Eng C 79
(Supple-ment C) (2017) 958e971
[2] M.F Akhtar, M Hanif, N.M Ranjha, Methods of synthesis of hydrogels … A
review, Saudi Pharmaceut J 24 (5) (2016) 554e559
[3] T Thanyacharoen, et al., The chemical composition and antioxidant and
release properties of a black rice (Oryza sativa L.)-loaded chitosan and
poly-vinyl alcohol composite, J Mol Liq 248 (2017) 1065e1070
[4] T Thanyacharoen, et al., Development of a gallic acid-loaded chitosan and
polyvinyl alcohol hydrogel composite: release characteristics and antioxidant
activity, Int J Biol Macromol 107 (Part A) (2018) 363e370
[5] W Treesuppharat, et al., Synthesis and characterization of bacterial cellulose
and gelatin-based hydrogel composites for drug-delivery systems, Biotechnol.
Rep 15 (2017) 84e91
[6] J Juntaro, et al., Bacterial cellulose reinforced polyurethane-based resin
nanocomposite: a study of how ethanol and processing pressure affect
physical, mechanical and dielectric properties, Carbohydr Polym 87 (4)
(2012) 2464e2469
[7] S Ummartyotin, et al., Development of transparent bacterial cellulose
nano-composite film as substrate for flexible organic light emitting diode (OLED)
display, Ind Crop Prod 35 (2012) 92e97
[8] K O-Rak, et al., Development of bacterial cellulose and poly(vinylidene
fluo-ride) binary blend system: structure and properties, Chem Eng J 237 (2014)
396e402
[9] J Wang, et al., Preparation and in vitro characterization of BC/PVA hydrogel
composite for its potential use as artificial cornea biomaterial, Mater Sci Eng.
C 30 (1) (2010) 214e218
[10] X Gao, et al., Time-dependent rheological behaviour of bacterial cellulose
hydrogel, Mater Sci Eng C 58 (Supplement C) (2016) 153e159
[11] X Gao, et al., Assessing stiffness of nanofibres in bacterial cellulose hydrogels: numerical-experimental framework, Mater Sci Eng C 77 (Supplement C) (2017) 9e18
[12] Y Wang, et al., Synthesis of cellulose-based double-network hydrogels demonstrating high strength, self-healing, and antibacterial properties, Car-bohydr Polym 168 (Supplement C) (2017) 112e120
[13] S Butylina, S Geng, K Oksman, Properties of as-prepared and freeze-dried hydrogels made from poly(vinyl alcohol) and cellulose nano-crystals using freeze-thaw technique, Eur Polym J 81 (Supplement C) (2016) 386e396
[14] N Lin, et al., Surface acetylation of cellulose nanocrystal and its reinforcing function in poly(lactic acid), Carbohydr Polym 83 (4) (2011) 1834e1842 [15] H Yan, et al., Synthesis of bacterial cellulose and bacterial cellulose nano-crystals for their applications in the stabilization of olive oil pickering emul-sion, Food Hydrocoll 72 (Supplement C) (2017) 127e135
[16] X Qi, et al., Investigation of Salecan/poly(vinyl alcohol) hydrogels prepared
by freeze/thaw method, Carbohydr Polym 118 (Supplement C) (2015) 60e69
[17] N Saba, et al., Thermal and dynamic mechanical properties of cellulose nanofibers reinforced epoxy composites, Int J Biol Macromol 102 (Supple-ment C) (2017) 822e828
[18] M.G Cascone, et al., Effect of chitosan and dextran on the properties of poly(vinyl alcohol) hydrogels, J Mater Sci Mater Med 10 (7) (1999) 431e435
[19] I Mihaela Jipa, et al., Preparation and characterization of bacterial cellulose-poly(vinyl alcohol) films with antimicrobial properties, Mater Lett 66 (1) (2012) 125e127
[20] C.M Hassan, N.A Peppas, Structure and morphology of freeze/thawed PVA hydrogels, Macromolecules 33 (2000) 2472e2479
[21] M.V Dinu, et al., Morphological and swelling properties of porous hydrogels based on poly(hydroxyethyl methacrylate) and chitosan modulated by ice-templating process and porogen leaching, J Polym Res 20 (2013) 11 [22] J.A Sirvi €o, et al., Composite films of poly(vinyl alcohol) and bifunctional cross-linking cellulose nanocrystals, ACS Appl Mater Interfaces 7 (35) (2015) 19691e19699
[23] M.B.K Niazi, et al., Mechanical, thermal and swelling properties of phos-phorylated nanocellulose fibrils/PVA nanocomposite membranes, Carbohydr Polym 177 (2017) 258e268
[24] A Mandal, D Chakrabarty, Characterization of nanocellulose reinforced semi-interpenetrating polymer network of poly(vinyl alcohol) & polyacrylamide composite films, Carbohydr Polym 134 (2015) 240e250
N Chunshom et al / Journal of Science: Advanced Materials and Devices 3 (2018) 296e302 302