Tuning the Chemical and Thermo-Mechanical Properties of Cassava Starch Thin Films to Produce Biodegradable Packaging Materials

Abstract

Starch is a renewable resource and starch films play a vital role as an alternative for synthetic polymers in packaging applications. However, the films prepared from native starch fail to meet the process or product requirements due to high water absorption and inferior mechanical properties. In order to avoid these drawbacks, and to enhance the desired properties, starch can be modified using acid hydrolysis. In this study, the effects of acid hydrolysis time on the structural, thermal, and chemical properties of cassava starch and cassava starch thin films were investigated. Native cassava starch was hydrolyzed using 2.2 M hydrochloric acid with varying time intervals. With the increase of hydrolysis time, the relative crystallinity of cassava starch increased while the thermal decomposition temperature decreased in cassava starch. XRD and 13C-NMR spectrums results show that, cassava starch has been subjected to polymorphism changes from A (monoclinic cell) to B (hexagonal unit cell) due to the acid hydrolysis treatment. FTIR and TGA analysis showed that, the moisture absorbance of cassava starch decreased significantly as a result of the acid hydrolysis treatment. The acid hydrolyzed samples showed up to 31.79 % reduction of moisture content compared to the native starch samples. Also, the films prepared from acid hydrolyzed starch showed up to 25.12% reduction of water absorption compared to that prepared from native starch. Acid hydrolysis treatment significantly impacted the mechanical behavior of starch-based films. The tensile strength of cassava starch-based films improved continuously with acid hydrolysis time, reaching a maximum of 5.67 MPa. However, the ductility of the films was negatively impacted when the starch was subjected to acid hydrolysis. The films prepared using acid hydrolyzed starch showed a 12.78 % reduction of elongation compared to that prepared with native cassava starch, despite with minimum dependence of acid hydrolysis time.