Effect of amylose contents of starches on physical properties and biodegradability of starch/PVA-blended films

Abstract

Recently, synthetic plastics are used widely in various fields, and with increased applications, disposal of waste plastics has become a serious problem. Therefore, development of novel plastics that are degradable by microorganisms in soil has recently been attracting much attention. In this study, starch/PVA-blended films were prepared from commercial starches with the different amylose contents, PVA, and additives by using a simple mixing process and casting method. Glycerol (GL), sorbitol (SO), tartaric acid (TA), and citric acid (CA) were used as additives. The physical properties such as tensile strength (TS), elongation at break (%E), degree of swelling (DS), and solubility (S) with amylose contents of starches were investigated. The amylose content of starches was analyzed by the colorimetric method. Thermal analysis of films was measured by using a differential scanning calorimeter (DSC). Finally, biodegradability of the films was evaluated in a 6-month soil burial test. The examination of the physical properties of biodegradable films indicates that with the higher amylose contents of starch used in preparing the film, TS, and DS of films increased, whereas %E and S decreased. The additives containing both carboxyl and hydroxyl groups, i.e. TA and CA, improved the physical properties of films. A thermal analysis of films revealed that the glass transition temperature (Tg) rose because of the increased crystallization of films with the increasing the amylose contents. Also, films degraded rapidly at the beginning and slow degradation took place until the experiment was completed. The films showed 50–80% degradation.