31. Cellulose-glycerol-polyvinyl alcohol composite films for food packaging: Evaluation of water adsorption, mechanical properties, light-barrier properties and transparencyPatricia Cazón, Manuel Vazquez, Gonzalo Velazquez, 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. Keywords: Cellulose, Toughness, Burst strength, Distance to burst, Water adsorption, Transparency Published in RUNG: 14.12.2020; Views: 2599; Downloads: 0 This document has many files! More... |
32. Novel composite films from regenerated cellulose-glycerol-polyvinyl alcohol: Mechanical and barrier propertiesPatricia Cazón, Gonzalo Velazquez, Manuel Vazquez, 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. Keywords: Regenerated cellulose, Tensile strength, Water vapor permeability, Anti-plasticizer, DSC, UV protection Published in RUNG: 14.12.2020; Views: 2472; Downloads: 0 This document has many files! More... |
33. Characterization of bacterial cellulose films combined with chitosan and polyvinyl alcohol: Evaluation of mechanical and barrier propertiesPatricia Cazón, Gonzalo Velazquez, Manuel Vazquez, 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. Keywords: Films, Bacterial cellulose, Water vapor permeability, Chitosan, Polyvinyl alcohol, UV protection Published in RUNG: 14.12.2020; Views: 2431; Downloads: 0 This document has many files! More... |
34. Regenerated cellulose films combined with glycerol and polyvinyl alcohol: Effect of moisture content on the physical propertiesPatricia Cazón, Gonzalo Velazquez, Manuel Vazquez, 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. Keywords: Adsorption isotherms, Plasticization, Regenerated cellulose, Water vapour permeability, Moisture content Published in RUNG: 09.12.2020; Views: 2589; Downloads: 0 This document has many files! More... |
35. Regenerated cellulose films with chitosan and polyvinyl alcohol: Effect of the moisture content on the barrier, mechanical and optical propertiesPatricia Cazón, Manuel Vazquez, Gonzalo Velazquez, 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. Keywords: Adsorption isotherms, Plasticization, Regenerated cellulose, Chitosan, Polyvinyl alcohol, Water vapour permeability, Moisture content Published in RUNG: 09.12.2020; Views: 2830; Downloads: 0 This document has many files! More... |
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37. Studies on the response of a water-Cherenkov detector of the Pierre Auger Observatory to atmospheric muons using an RPC hodoscopeA. Aab, Andrej Filipčič, Gašper Kukec Mezek, Samo Stanič, Marta Trini, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2020, original scientific article Keywords: ultra-high energy cosmic rays, extensive air showers, Pierre Auger Observatory, water Cherenkov detectors, detector calibration, hodoscope-based calibration Published in RUNG: 11.09.2020; Views: 3278; Downloads: 111 Full text (1,39 MB) |
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40. Highly efficient carcinogenic bromate removal from water by a cationic covalent organic frameworkTina Skorjanc, Dinesh Shetty, Felipe Gandara, Liaqat Ali, Ali Trabolsi, 2019, published scientific conference contribution abstract Keywords: bromate, covalent organic frameworks, Zincke reaction, adsorption, water purification Published in RUNG: 03.09.2020; Views: 2933; Downloads: 0 This document has many files! More... |