Thermoplastic starch from corn and wheat: a comparative study based on amylose content

This study comes as a part of the recent efforts aimed to face the challenges of environmental pollution by non-degradable plastic. Thermoplastic starch is classified as one of those materials extensively investigated for its use as an alternative to fossil-based plastic for many applications. Since the starch is a natural material that could be extracted from different plant sources, the properties of produced thermoplastic starch vary according to the starch’s biological origin. Herein, the rheological, structure, thermal and mechanical properties of thermoplastic starches prepared from two kinds of cereal starches (wheat and corn) that are mainly different in amylose content were studied. The same processing conditions were applied on both native starches to accomplish the phase transition from granules to molten thermoplastic state and the Torque, X-ray Diffraction (XRD), Thermogravimetric analysis (TGA) and Scanning Electron Microscopy (SEM) analysis were used to prove this transition. It was noticed by XRD and SEM that both thermoplastic starches contain remnants of granules and granules fragments and their ratio was higher in thermoplastic wheat starch. Besides that, Torque analysis showed that higher torque was required to reach steady-state during the plasticization process in wheat starch than in corn starch. This behavior can be attributed to the higher ratio of amylose in wheat starch than corn starch. The difference in the ability of each type of starch to form hydrogen bonds with plasticizers was studied by FT-IR and the outcome this analysis agreed with TGA analysis. The results showed that the wheat starch had a higher ability to form strong hydrogen bonds with plasticizers than corn starch. Finally, the mechanical properties were investigated and the results revealed a direct relation between these properties and amylose content.