| The main objective of this research was to investigate and compare the optical, physical, mechanical and barrier properties of polylactide with the properties of standard polymers such as polyethylene terephthalate (PET) and polystyrene (PS) used in packaging applications. In addition, the experimental values of the different properties were compared with theoretical predicted values. Finally, the total migration of polylactides (PLA) in food simulant solutions was measured.; PLA polymer shows better ultraviolet light barrier properties than polyethylene, but slightly worse than cellophane, PS, and PET. Density values, surface tension, and friction coefficient of PLA resins are in agreement with the theoretical predicted values. PLA has lower melting and glass transition temperatures than PET and PS, which makes PLA better for heat sealing and thermal processing; however, the glass transition temperature of PLA polymers changes with time. Humidity and temperature did not have an effect on the transition temperature, which can be explained by the lower water sorption values of PLA (i.e., <100 ppm at Aw = 1).; PLA shows good sealing at temperatures below the melting temperature, however, an appreciable shrinking of the films was found when the material was sealed near the melting temperature. Regarding mechanical properties, PLA showed similar tensile strength values to PS but lower than PET; in addition, compression strength of PLA bottles and containers was lower than PET.; Solubility parameter predictions indicate that PLA may show interaction mainly with nitrogen compounds, anhydrides, and some alcohols, and it will not interact with aromatic hydrocarbons, ketones, esters, sulfur compounds, and water. In terms of barrier, PLA showed CO2 and O2 permeability coefficients that are lower than PS and comparable to those of PET. An increase of the oxygen permeability coefficient of PET and PLA was observed as temperature increased. Oxygen diffusion in PET and PLA showed an exponential increase as water activity increased, at each temperature. The permeability coefficients of PET and PLA decreased as the water content increased. The effect is more pronounced at higher temperatures. The oxygen solubility coefficient decreased linearly as the water activity increased, mainly due to the reduction in free volume because of its occupation by the water molecules. (Abstract shortened by UMI.)... |
