Browsing by Subject "film"
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(2013)Increasing the use of biodegradable packaging materials could reduce the need of petroleumbased plastics. Hemicelluloses are a potential source of renewable raw material for packaging purposes. The literature review focused on polysaccharide-based packaging materials and properties of food packaging materials. In addition, crosslinking polysaccharides with citric acid and ammonium zirconium carbonate (AZC) were discussed. The objective of the experimental study was to prepare self-standing films from spruce galactoglucomannan (GGM), and to study their properties. The aim was to enhance the mechanical and permeability properties, and make the films less sensitive to moisture, via crosslinking. Crosslinking was carried out in solution and sorbitol was used as plasticiser. The films were prepared by a casting method and dried at room temperature. Tensile strength, elongation at break and Young’s modulus were measured by tensile testing. In addition, oxygen permeabi lity, water vapour permeability and water solubility of films were measured. The effect of moisture on films was investigated with sorption isotherm and humidity scanning dynamic mechanical analysis. Citric acid did not function as a crosslinking agent, but acted more as a plasticiser increasing elongation. The heating required for the crosslinking reaction should be performed in dry film instead of solution. Crosslinking with AZC resulted in strong films, with tensile strength up to 52 MPa. Sorbitol addition decreased the tensile strength and Young’s modulus, but increased the elongation, as expected. Crosslinking and sorbitol addition both decreased water vapour permeability, resulting in a better water vapour barrier. The deviations in oxygen permeability measurements were high, but it looks like crosslinking with AZC results in better oxygen barrier. In high relative humidity (RH) the film with AZC absorbed less water vapour and the storage modulus decreased slower than in the non-crosslinked film. Thus, crosslinking with AZC made the properties of GGM films less susceptible to changes in RH. AZC appears to be a promising crosslinking agent for hemicellulose films, therefore the suitability for food packaging applications should be further studied.
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(2016)In the literature review of this study, the focus was on biofilms that certain microbes produce, and their potential use in food industry. Biofilms consist of microbial cells and extracellular products, e.g., polysaccharides. Pullulan as an exopolysaccharide has many industrial applications and the aim of this study was to explore a new potential alpha-glucan, dextran, and especially its ability to form a stand-alone film. Pullulan and dextran were separately mixed in de-ionized water. The dynamic viscosities of dextran and pullulan solutions were determined. Film formation of dextran was not successful, not even with sorbitol as a plasticizer. The optical properties, water vapor and oxygen permeabilities and tensile strengths of pullulan films were studied. Additionally, Whatman42-filter material was coated with or immersed in dextran solution. Hence the changes in tensile strength and permeability values between a well-known material and dextran treated material could be detected. Pullulan films had low haze values (2.1–3.9%) and they were transparent to UVA-, UVB- and visible light. The tensile strength values of pullulan films were 47–53 MPa. For filter paper, the corresponding values were 10 MPa and application of dextran coating increased it to 15–19 MPa. All polysaccharide solutions exhibited Newtonian behavior and their relative viscosities were <10 mPa, 5% pullulan with viscosity around 20 mPa as an exception. Pullulan solutions had higher viscosities than dextran solutions. The air permeabilities were 10–50 ml/min for pullulan films, 10 ml/min for dextran-sorbitol film, 200 ml/min for dextran film and 200–500 ml/min for Whatman42 material. The oxygen permeability values for pullulan films were <0,1 cm3·μm m-2·d-1·kPa-1. Based on results in this study, pullulan films are impermeable to oxygen. As the films tolerated water vapor poorly, pullulan might be a potential component in packages made of composite materials, as individual packaging material in dry environment or possibly chemically modified to obtain better resistance to water vapor. Our results show that without additional modifications dextran does not form a continuous self-supporting films in these conditions.
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