Treatment and mechanism for hot melting starch by reducing the molecular chain winding and crystallinity

Unlike thermoplastic petroleum-based materials, starch-based materials rely on aqueous systems but are incapable of hot melting, resulting in low processing efficiency and limited large-scale industrial applications. In this study, the combination of α-amylase liquefaction and urea plasticization was used for the first time to obtain enzymatic thermoplastic starch (ETPS) for hot melting by changing the molecular chain of starch. ETPS showed an apparent hot melting phenomenon when heated below 200 °C. Differential scanning calorimetry revealed that heat absorption peaks were obviously reduced, and the hot melting phenomenon occurred easily depending on the combination of enzymatic hydrolysis and plasticization. Dynamic mechanical analysis indicated that the combined modification effectively increased the number of freely movable chains. The red shift of -OH stretching vibration peaks indicated the formation of strengthened hydrogen bonds in ETPS. X-ray diffraction showed that the crystallinity of ETPS was reduced to 5.68 %, effectively reducing the regenerative phenomenon. Gel permeation chromatography revealed that the molecular weight of ETPS decreased, and the entanglements between molecular chains were reduced. A tensile test showed that the elongation at break of ETPS was as high as 235.29 %, which was much higher than those of enzymatic hydrolysis starch and thermoplastic starch.