Browsing by Subject "mekaaniset ominaisuudet"

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  • Pulkkinen, Jukka (Helsingfors universitet, 2011)
    Emulsified films are prepared by drying an emulsion. Polysaccharide based emulsified films consist of film-forming polysaccharide, fat, emulsifier and plasticiser. In the literature review, the materials used in the preparation of polysaccharide based emulsified films were discussed. The review also included a discussion of which factors affect the water barrier and mechanical properties of the emulsified films. The aim of the experimental study was to find out the potential of konjac glucomannan (KGM) and galactoglucomannan (GGM) in emulsified films. The effect of fat type and fat content on the water barrier and mechanical properties of the films were studied. Emulsified films which contained 30% (wt-% of GGM) fat were prepared from beeswax, rapeseed oil and pine wood oil. Fat contents of 10 and 50% were also used for beeswax. Emulsified films were compared with control films that did not contain any fat. The ratio of KGM and GGM used was 1:1. The water vapour permeability (WVP), water vapour transmission rate (WVTR), Young’s modulus, tensile strength and elongation at break were measured. Films were also viewed with a scanning electron microscope (SEM). KGM and GGM were suitable materials for emulsified films. The surfaces of films dried at room temperature were more uniform than those dried at 60 °C. In the SEM images, wax droplets were smaller than oil droplets. The diameter of oil droplets was about 10 ?m and 2–6 ?m for wax droplets. Wax droplets were better entrapped in the film matrix probably due to their smaller size. As expected, best water barrier properties were obtained with films containing 50% beeswax (p < 0.05). WVP of the films decreased when the content of beeswax in the film increased. Films containing 30% oils and 10% beeswax did not differ significantly from the control film in water barrier and in mechanical properties. The lowest Young’s modulus was with 50% beeswax film. The control film was the stiffest and strongest. There were no statistically significant differences in elongation at break between the films. Emulsified films were successfully prepared from KGM and GGM. The water barrier properties of emulsified films were better than those of the control film and still the mechanical properties were rather well maintained.
  • Schmidt, Jutta (Helsingfors universitet, 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.