Starch-based biodegradable composites: Effects of in-situ re-extrusion on structure and performance

In this study, starch-based biodegradable composites (SDC) were prepared by extruding using thermoplastic starch (TPS, 65%wt), polylactic acid (PLA, 30%wt) and poly (butylene adipate co-terephthalate) (PBAT, 5%wt). Structure and properties of the SDC were compared by performing 1-, 2-, 3-times extrusion. The results show that in-situ re-extrusion refines the TPS in composites and reduces the size of the phase. As the number of extrusions increases, the ester bond of composites at 868 cm^-1 disappears, the crystallinity increases, and the thermal stability decreases. Among the three types of composites, the mechanical properties and hydrophobic properties of the material obtained by the 2-times are the most outstanding. Compared with SDC, the elongation at break and Young's modulus of SDC-2 are significantly increased, with an increase of 8.01 % and 1.28 % in the machine direction and an increase of 11.02 % and 1.79 % in the transverse direction respectively. Additionally, water contact angle range of SDC-2 from 98.7° to 101.7°. Therefore, SDC prepared by 2-times in-situ re-extrusion has the best film properties and is an ideal packaging material. This study presents a novel method for fabricating starch-degradable composite films by in-situ re-extrusion, providing new insights into the development of starch packaging materials.