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1.
UV-protecting films based on bacterial cellulose, glycerol and polyvinyl alcohol: effect of water activity on barrier, mechanical and optical properties
Manuel Vazquez, Gonzalo Velazquez, Patricia Cazon, 2020, original scientific article

Abstract: Biodegradable films based on bacterial cellulose, glycerol and polyvinyl alcohol are a new alternative to develop food packaging with the capac- ity to retard or inhibit the effect of UV radiation. However, these compounds are sensitive to moisture. Therefore, the purpose of this study was to evaluate the modifications of the mechanical, water vapor permeability and optical properties of these composite films depending on their water activity. Results showed that water molecules acted as a plasticizer agent, modifying the mechanical, water vapor perme- ability and optical properties of the developed films. However, an overplastification process took place at higher activity water, resulting in a weakness of film structure and decreasing drastically the elongation. The transmittance in the UV–VIS light region decreased when the activity water increased. No significant variations were observed in color, trans- parency or opacity properties.
Found in: osebi
Keywords: GAB model, Moisture adsorption isotherms, Plasticization, Bacterial cellulose, Mechanical properties, UV-barrier properties
Published: 09.12.2020; Views: 460; Downloads: 20
.pdf Fulltext (552,03 KB)

2.
Bacterial cellulose films: Evaluation of the water interaction
Manuel Vazquez, Gonzalo Velazquez, Patricia Cazon, 2020, original scientific article

Abstract: Bacterial cellulose is a biopolymer that is gaining attention due to its 3D structure, higher purity, porosity and surface area. However, this material can interact with water molecules from the surrounding environment, resulting in alterations of its properties. Hence, the purpose of this study was to analyze the modifications on the mechanical, water vapor permeability and optical properties of bacterial cellulose films as a function of the water activity. Results indicated that water acted as a plasticizer, mainly affecting mechanical and water vapor permeability properties. The moisture adsorption isotherms allowed predicting the moisture content of the bacterial cellulose films at several relative humidity conditions. Values for tensile strength and burst strength ranged from 15.50 to 22.28 MPa and from 145.03–338.10 g, respectively. The elongation and the distance to burst ranged from 1.36 to 3.71 % and from 0.39 to 1.86 mm, respectively. These values increased due to the plasticizing effect of the water molecules. Water vapor permeability values ranged from 1.35·10−12 to 3.13·10-11 g/ m s Pa, showing a significant increase up to 0.48 of water activity. Bacterial cellulose films showed excellent UV-barrier properties in the different water activities evaluated.
Found in: osebi
Keywords: GAB model, Moisture adsorption isotherms, Bacterial cellulose, Mechanical properties, UV-barrier properties
Published: 09.12.2020; Views: 415; Downloads: 0
.pdf Fulltext (1,02 MB)

3.
Regenerated cellulose films with chitosan and polyvinyl alcohol: Effect of the moisture content on the barrier, mechanical and optical properties
Gonzalo Velazquez, Manuel Vazquez, Patricia Cazon, 2020, original scientific article

Abstract: The aim of this research was to evaluate the effect of moisture content on the mechanical, barrier and optical properties of films obtained from regenerated cellulose with chitosan and polyvinyl alcohol equilibrated at several relative humidity conditions. The experimental moisture adsorption isotherms were fitted using the Guggenheim-Anderson-DeBoer model. The adsorption isotherm showed a typical type II sigmoidal shape. The highest moisture content (27.53 %) was obtained at a water activity of 0.9. The water vapour permeability values increased up to 6.34·10−11 g/ m s Pa as the moisture content of the films increased. Tensile strength, percentage of elongation, Young’s modulus, burst strength and distance to burst showed a significant plasticizing effect of the water molecules. Results suggest that interactions between film components and water molecules decrease the transmittance in the UV region and the transparency. Consequently, water molecules improve the UV-barrier properties of the films and increasing the opacity.
Found in: osebi
Keywords: Adsorption isotherms, Plasticization, Regenerated cellulose, Chitosan, Polyvinyl alcohol, Water vapour permeability, Moisture content
Published: 09.12.2020; Views: 472; Downloads: 0
.pdf Fulltext (588,35 KB)

4.
Regenerated cellulose films combined with glycerol and polyvinyl alcohol: Effect of moisture content on the physical properties
Manuel Vazquez, Gonzalo Velazquez, Patricia Cazon, 2020, original scientific article

Abstract: Regenerated cellulose-based films combined with glycerol and polyvinyl alcohol (PVOH) show interesting UV- light barrier properties, with potential application in food packaging to prevent oxidative deterioration. How- ever, these materials are sensitive to moisture, and their properties could be modified as a function of the relative humidity. Hence, the objective of the present work was to evaluate the changes in the main properties of re- generated cellulose-glycerol-PVOH films depending on the relative humidity. Using the GAB adsorption iso- therms, the moisture content was related with the water activity of the films at several relative humidity conditions. According to the obtained results, water molecules manifested a plasticizing effect modifying the mechanical, water vapour permeability and optical properties of the developed films. Tensile strength and Young’s modulus values ranged from 92.65 to 17.57 MPa and from 3639.09 to 227.89 MPa, respectively. Both of them decreased when the moisture content increased. The mechanical resistance to deformation of films enhanced at high moisture content, changing from 5.88 to 15.97% and from 0.59 to 2.97 mm in the tensile and puncture test, respectively. This effect was also observed for the burst strength. Water vapour permeability increased from 5.15⋅10?10 to 5.44⋅10?9 g/ms Pa when the moisture content increased, being more significative at higher values. No significant variations were observed in the UV-VIS transmittance at different moisture contents. The obtained results allow expanding the knowledge of the behavior of films based on regenerated cellulose.
Found in: osebi
Keywords: Adsorption isotherms, Plasticization, Regenerated cellulose, Water vapour permeability, Moisture content
Published: 09.12.2020; Views: 450; Downloads: 0
.pdf Fulltext (522,58 KB)

5.
Environmentally Friendly Films Combining Bacterial Cellulose, Chitosan, and Polyvinyl Alcohol: Effect of Water Activity on Barrier, Mechanical, and Optical Properties
Gonzalo Velazquez, Manuel Vazquez, Patricia Cazon, 2019, original scientific article

Abstract: The interest in developing new materials intended for food packaging based on bacterial cellulose is growing in the recent years. Flexible and transparent films from bacterial cellulose-chitosan-polyvinyl alcohol have shown excellent UV-barrier properties. However, this composite material interacts with ambient moisture modifying its water activity due to its hydrophilic nature. In this work, an extensive study was carried out to evaluate the changes in the properties of these films as a function of water activity. Moisture adsorption isotherm were described by the GAB method. Results showed the plasticizing effect of water molecules increasing the water vapour permeability of the samples from 1.86·10-12 to 1.17·10-11 g/m·s·Pa, the percentage of elongation from 3.25 to 36.55% and the distance to burst from 0.64 to 5.12 mm. The increase of the water activity dropped the tensile strength values from 74.76 to 38.56 MPa, Young’s modulus values from 3133.46 to 30.71 MPa and burst strength to 703.87 g. The values of the UV-barrier were maintained at the wide range of water activity. Consequently, water molecules do not affect the UV-barrier properties of the films.
Found in: osebi
Keywords: GAB model, moisture adsorption isotherms, plasticization, bacterial cellulose, mechanical properties, UV-barrier properties, moisture content
Published: 09.12.2020; Views: 410; Downloads: 0
.pdf Fulltext (483,23 KB)

6.
Characterization of mechanical and barrier properties of bacterial cellulose, glycerol and polyvinyl alcohol (PVOH) composite films with eco-friendly UV-protective properties
Manuel Vazquez, Gonzalo Velazquez, Patricia Cazon, 2020, original scientific article

Abstract: Highly flexible composite films based on bacterial cellulose, glycerol and polyvinyl alcohol (PVOH) with UV barrier properties were developed. The open nanoscale network of bacterial cellulose allowed to combine it with glycerol and polyvinyl alcohol by immersion. This procedure kept intact the bacterial cellulose structure. The interactions among bacterial cellulose, glycerol and PVOH were analyzed using scanning electron microscopy, infrared spectroscopy, thermogravimetry and differential scanning calorimetry. In general, the addition of PVOH reinforced the bacterial cellulose matrix, meanwhile glycerol showed a significant plasticizing effect. Formulations with PVOH and glycerol reached a maximum value of 49.89% of elongation and a good resistance to rupture of 13.78 MPa. The water vapour permeability ranged from 1.87·10−11 to 2.04·10−10 g/m s Pa. The UV-VIS spectral analysis showed that glycerol decreased the transmittance in the UV area and polyvinyl alcohol enhanced the transparency values of the samples in the VIS region. The transmittance in the UV-A, UV-B and UV- C areas for films based on bacterial cellulose with glycerol reached up to 5.59, 2.4 and 0.57%, respectively.
Found in: osebi
Keywords: Acetobacter xylinum, Tensile strength, Percentage of elongation at break, Young's modulus, Eco-friendly film
Published: 14.12.2020; Views: 349; Downloads: 0
.pdf Fulltext (2,12 MB)
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7.
Composite films with UV-barrier properties of bacterial cellulose with glycerol and polyvinyl alcohol: puncture properties, solubility and swelling degree
Gonzalo Velazquez, Manuel Vazquez, Patricia Cazon, 2019, original scientific article

Abstract: The aim of this study was to develop composite films based on bacterial cellulose, glycerol, and poly(vinyl alcohol) with improved optical and mechanical properties and good UV-barrier property. The interaction among the compounds was analyzed using Fourier transform infrared spectroscopy, scanning electron microscopy, ther- mogravimetry, and differential scanning calorimetry. The mechanical properties (toughness, burst strength, and distance to burst), solubility, water adsorption, and light barrier properties of the composite films were evaluated. Polynomial models obtained allowed us to predict the behavior of these properties. Poly(vinyl alcohol) showed a reinforcing effect on the bacterial cellulose matrix, while glycerol showed a noticeable plasticizing behavior. The bacterial cellulose-based composites showed toughness values ranging from 0.22 to 2.60 MJ/m3. The burst strength values obtained ranged between 43.74 and 2105.52 g. The distance to burst ranged from 0.39 to 4.94 mm. The film solubility on water ranged from 9.37 to 31.65%, and the water retention ranged from 78.26 to 364.78%. Glycerol decreased the transmittance in the UV region, improving the UV- barrier properties of the films, while poly(vinyl alcohol) improved the transparency and opacity values of the samples. The transmittance in the UV regions (A, B, and C) ranged from 1 to 48.51%, increasing with the poly(vinyl alcohol) concentration.
Found in: osebi
Keywords: DSC, FT-IR, SEM, UV protection
Published: 14.12.2020; Views: 319; Downloads: 0
.pdf Fulltext (2,12 MB)
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8.
Characterization of bacterial cellulose films combined with chitosan and polyvinyl alcohol: Evaluation of mechanical and barrier properties
Manuel Vazquez, Gonzalo Velazquez, Patricia Cazon, 2019, original scientific article

Abstract: Bacterial cellulose (BC) produced by Komagataeibacter xylinus is a biomaterial with a unique three-dimensional structure. To improve the mechanical properties and reinforce the BC films, they were immersed in polyvinyl alcohol (0–4%) and chitosan (0–1%) baths. Moisture content, mechanical properties and water vapour perme- ability were measured to assess the effect of polyvinyl alcohol and chitosan. The morphology, optical, structural and thermal properties were evaluated by scanning electron microscopy, spectral analysis, thermogravimetry and differential scanning calorimetry. Results showed that moisture content was significantly affected by the chitosan presence. Tensile strength values in the 20.76–41.65 MPa range were similar to those of synthetic polymer films. Percentage of elongation ranged from 2.28 to 21.82% and Young's modulus ranged from 1043.88 to 2247.82 MPa. The water vapour permeability (1.47×10−11–3.40×10−11 g/m s Pa) decreased with the addition of polyvinyl alcohol. The developed films own UV light barrier properties and optimal visual appearance.
Found in: osebi
Keywords: Films, Bacterial cellulose, Water vapor permeability, Chitosan, Polyvinyl alcohol, UV protection
Published: 14.12.2020; Views: 372; Downloads: 0
.pdf Fulltext (1,78 MB)
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9.
Novel composite films from regenerated cellulose-glycerol-polyvinyl alcohol: Mechanical and barrier properties
Manuel Vazquez, Gonzalo Velazquez, Patricia Cazon, 2019, original scientific article

Abstract: Cellulose is considered as an alternative for the demand of biocompatible and environmentally friendly food packaging. The aim of this study was to evaluate a composite film from regenerated cellulose combined with polyvinyl alcohol. Glycerol was used as a plasticizer. Mathematical models were used to describe the effect of the film structure on the mechanical (tensile strength, percentage of elongation at break) and barrier properties (water vapour permeability, light-barrier properties and transparency). The morphology, structural and thermal properties were evaluated by spectral analysis (FT-IR and UV-VIS-NIR), scanning electron microscopy and dif- ferential scanning calorimetry. Models predict cellulose-glycerol-polyvinyl alcohol films with tensile strength values from 25.9 to 369 MPa, similar to that of synthetic polymer films. The elongation at break of the developed films (0.89–18.7%) was lower than that of synthetic polymer films. The water vapour permeability obtained (2.32·10−11 - 3.01·10−11 g/s·m·Pa) was higher than that of petrochemical-based plastics. Cellulose films re- inforced with polyvinyl alcohol showed a smooth surface. Results showed that it is viable to accomplish com- posite films from cellulose-polyvinyl alcohol-glycerol with enhanced mechanical properties. The obtained films showed top values of transparency. The addition of glycerol resulted in films with a UV protective effect which could be important in food packaging to prevent lipid oxidative deterioration.
Found in: osebi
Keywords: Regenerated cellulose, Tensile strength, Water vapor permeability, Anti-plasticizer, DSC, UV protection
Published: 14.12.2020; Views: 394; Downloads: 0
.pdf Fulltext (727,71 KB)

10.
Cellulose-glycerol-polyvinyl alcohol composite films for food packaging: Evaluation of water adsorption, mechanical properties, light-barrier properties and transparency
Gonzalo Velazquez, Manuel Vazquez, Patricia Cazon, 2018, original scientific article

Abstract: Nowadays consumers are aware of environmental problems. As an alternative to petrochemical polymers for food packaging, researchers have been focused on biopolymeric materials as raw material. The aim of this study was to evaluate mechanical properties (toughness, burst strength and distance to burst), water adsorption, light- barrier properties and transparency of composite films based on cellulose, glycerol and polyvinyl alcohol. Scanning electron microscopy, spectral analysis (FT-IR and UV–VIS-NIR) and differential scanning calorimetry were performed to explain the morphology, structural and thermal properties of the films. Results showed that polyvinyl alcohol enhances the toughness of films up to 44.30 MJ/m3. However, toughness decreases when glycerol concentration is increased (from 23.41 to 10.55 MJ/m3). Water adsorption increased with increasing polyvinyl alcohol concentration up to 222%. Polyvinyl alcohol increased the film thickness. The films showed higher burst strength (up to 12014 g) than other biodegradable films. The films obtained have optimal values of transparency like those values of synthetic polymers. Glycerol produced a UV protective effect in the films, an important effect for food packaging to prevent lipid oxidative deterioration. Results showed that it is feasible to obtain cellulose-glycerol-polyvinyl alcohol composite films with improved properties.
Found in: osebi
Keywords: Cellulose, Toughness, Burst strength, Distance to burst, Water adsorption, Transparency
Published: 14.12.2020; Views: 397; Downloads: 0
.pdf Fulltext (3,13 MB)

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