Effect of pH on the physicochemical properties of starch films

We demonstrate a simple approach of using highly alkaline starch solutions to obtain films with high flexibility and improved water resistance. Extensive studies have been done to develop films from starch, primarily for food applications. However, films developed from starch are brittle and generally chemical modifications or plasticizers are used to improve the flexibility and other properties of starch films. Such modifications make starch expensive, decrease biodegradability, and affect the morphology and subsequent processing of starch. In this research, we have prepared films using starch solutions at pH between 3 and 11. Starch solutions having different pHs were made into films and the tensile, thermal properties, and resistance to water were studied. It was found that preparing starch with pH 11 solution imparts high flexibility without any apparent physical damage. Films prepared under strong acidic and alkaline conditions also had considerably reduced hydrophilicity, which is required for food packaging and other applications. The films prepared at alkaline pH show nearly 50% reduction in water sorption and an increase in elongation. The films obtained from alkaline pH are flexible and water resistant and can potentially be used to develop various bioproducts. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48563.