2.3. Film formation
Granular starch was dispersed in ultra-pure water (3% w/w) and gelatinized by stirring and heating to 75 °C followed by dissolution in an autoclave at 120 °C under 120 kPa pressure for 30 min. A clear, viscous solution was obtained. To this solution, glycerol (as plasticizer for the starch), 20% w/w relative to starch on a dry basis, was added. Starch/latex samples with ratios of 100/0, 95/05, 90/10, 85/15, 80/20 and 70/30 (w/w on a dry basis, that of the latex referring to the solid content obtained after drying at 60 °C) were made by adding latex to the starch/glycerol solution. The system was homogenized by vigorous shaking of the mixture. This was then poured on polystyrene dishes and allowed to dry at 25 °C over 3 days. The resulting films (20–50 μm in thickness) were then dried at 60 °C overnight and maintained at 54% relative humidity (r.h.) over a saturated solution of Mg(NO3)2 in a desiccator at room temperature.