Thermal processing of starch-based polymers

This paper reviews the thermal processing of starch-based polymers, including both fundamental science such as microstructure, phase transition and rheology, as well as processing techniques, conditions and formulations. The unique microstructure of starch and its multiphase transitions during thermal processing provide an outstanding model system to illustrate our conceptual approach to understanding the structure-processing-property relationships in polymers. One of the unique characteristics of starch-based polymers is their thermal processing properties, which are much more complex than conventional polymers, since multiple chemical and physical reactions may occur during processing, such as water diffusion, granular expansion, gelatinization, decomposition, melting and crystallization. Among these phase transitions, gelatinization is particularly important because it is closely related to the others, and it is the basis of the conversion of starch to a thermoplastic. Furthermore, the decomposition temperature of starch is higher than its melting temperature before gelatinization. Various conventional processing techniques such as extrusion, injection compression molding, and casting, as well as some new techniques such as reactive extrusion, have been adapted for processing starch-based polymers. The achievements in this area have increased our knowledge of polymer science, in particular that of natural polymers.