Enhancement of the properties of biodegradable rice starch films by using chemical crosslinking agents

The effect of chemical crosslinking on the mechanical, thermal properties and water vapor permeability of rice starch-based films were investigated. Epichlorohydrin (EPI), Sodium trimetaphosphate (STMP) and the mixing of STMP/STPP (Sodium tripolyphosphate) were used as crosslinking agents. The viscosity of crosslinked rice starch decreased when the content of the crosslinking agent increased concomitant with the increasing of the pasting temperature. The results showed that the degree of crosslinking increased when the content of the cross-linking agents increased. The tensile strength of rice starch films increased concomitantly with decreases in elongation at break and water vapor permeability when chemical-crosslinking was applied. In addition, the crosslinking reaction decreased the crystalline peak structure and percentage of crystallinity of rice starch films. The rice starch films were characterized by Fourier Transform infrared spectroscopy (FT-IR) and this confirmed that crosslinking between starches molecules had occurred. The behavior of thermal properties of crosslinked rice starch films were investigated by means of dynamic mechanical thermal analysis (DMTA) and using a differential scanning calorimeter (DSC). It was found that the glass temperature (Tg) of crosslinked rice starch films shifted to a higher temperature than that of untreated rice starch films. In addition, the storage modulus (E’) of crosslinked rice starch films decreased twice as much as untreated rice starch films, while the tan d curve of crosslinked rice starch film was higher than that of untreated rice starch films.