2311. Characterization of bacterial cellulose films combined with chitosan and polyvinyl alcohol: Evaluation of mechanical and barrier propertiesPatricia Cazón, Gonzalo Velazquez, Manuel Vazquez, 2019, izvirni znanstveni članek Opis: 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.
Ključne besede: Films, Bacterial cellulose, Water vapor permeability, Chitosan, Polyvinyl alcohol, UV protection
Objavljeno v RUNG: 14.12.2020; Ogledov: 2335; Prenosov: 0
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2312. Composite films with UV-barrier properties of bacterial cellulose with glycerol and polyvinyl alcohol: puncture properties, solubility and swelling degreePatricia Cazón, Manuel Vazquez, Gonzalo Velazquez, 2019, izvirni znanstveni članek Opis: 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.
Ključne besede: DSC, FT-IR, SEM, UV protection
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2313. Characterization of mechanical and barrier properties of bacterial cellulose, glycerol and polyvinyl alcohol (PVOH) composite films with eco-friendly UV-protective propertiesPatricia Cazón, Gonzalo Velazquez, Manuel Vazquez, 2020, izvirni znanstveni članek Opis: 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.
Ključne besede: Acetobacter xylinum, Tensile strength, Percentage of elongation at break, Young's modulus, Eco-friendly film
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2314. Applications of Chitosan as Food Packaging MaterialsPatricia Cazón, Manuel Vazquez, 2019, recenzija, prikaz knjige, kritika Opis: The interest in biopolymers has increased due to the depletion of the fossil fuel reserve and the environmental impact caused by the accumulation of non-biodegradable plastic-based packaging materials. Many biopolymers have been developed from food waste products to reduce this waste and, at the same time, to
obtain new food packaging materials. Chitosan is thus an alternative to synthetic polymers, and a raw material for new materials. To assess the suitability of a material as a food packaging material, it is necessary to study their mechanical and permeability properties. Mechanical properties allow to predict the behaviour of films during transportation, handling and storage of packaged foods. Barrier properties play a key
role in maintaining the food product quality. Properties values depend on the type of chitosan used. Mechanical and barrier properties of pure chitosan films are suitable for food packaging and active packaging. These properties can be modified by combining chitosan with other components such as plasticizers, other polysaccharides, proteins and lipids. These combinations adapt the properties of the final polymer to the needs of
the food to extend its useful life, while maintaining quality properties of the food and the biodegradability of the polymer.
Chitosan displays antimicrobial activity against a wide range of foodborne filamentous fungi, yeast, and gram-negative and gram-positive bacteria. This antimicrobial property and film-forming capacity has made chitosan the reference polymer to develop active packaging with the ability to inhibit the growth of microorganisms and improve food safety. Regarding the optical properties, pure chitosan films in the visible range show high transmittance values, being optically transparent films. This
is an important parameter related to the acceptability of the films by the consumer. In addition, chitosan-based films exhibit remarkable UV absorbance, which allows to protect food from lipid oxidations induced by UV radiation.
Ključne besede: Film, Mechanical properties, Barrier properties, Antimicrobial, UV
protect, Active food packaging
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2319. The Promise of Collective Authorship: Bela Balazs’s Move to the Soviet Union (1931-1946)Eszter Polonyi, prispevek na konferenci brez natisa Opis: Balazs belongs to a generation of Central and Eastern European critical thinker, cultural philosopher and writer that is often credited with exporting Marxist cultural analysis to North America, but about whom very little is known to English-language scholars. The fifteen years he spent in the Soviet Union are among the most undocumented of his career, even though this was when he wrote the text that would become his most widely-cited book, Theory of the Film. This paper examines Balazs’s decision to flee to the Soviet Union from Germany in 1931. While it has long been assumed that Balazs’s decision to move East rather than West—the route otherwise taken by colleagues of his such as Siegfried Kracauer, Michael Curtiz or Rudolf Arnheim—was due to commitments of a political nature, this paper evaluates Balazs’s options from the viewpoint of the scenarist’s rising importance within competing modes of film production. Pre-constituting a film by way of a plan, sketch or model, the scenario promised different types of leverage over production to capitalist and communist systems. Conceived of as a commodity blueprint in Hollywood, the scenario appeared as it was a means of enhancing the effectiveness of production and as a tool of capital, whereas, for Balazs at least, the scenario was a source of sensory and spiritual attunement between an assemblage of humans and machines. Understood as offering vision rather than oversight, collective authorship rather than collective control, the script appeared to complement the utopian arguments driving the Soviet film industry.
Ključne besede: film studies, industrial design, Soviet studies, authorship
Objavljeno v RUNG: 14.12.2020; Ogledov: 2117; Prenosov: 0
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