PREPARATION OF HIGH-TOUGHNESS THERMOPLASTIC STARCH FILMS VIA ENZYMATIC HYDROLYSIS AND CROSS-LINKING MODIFICATION

Unlike traditional petroleum-based thermoplastic films, starch-based films rely on solvent systems and cannot be processed thermally, resulting in low production efficiency and hindering large-scale industrial applications. This study developed a dual-modification method combining enzymatic hydrolysis, dual cross-linking, and plasticizers to prepare enzyme-crosslinked thermoplastic starch (ECSS). High-toughness and transparent films were fabricated via hot-pressing technology. Enzymatic hydrolysis reduced starch crystallinity and molecular chain entanglement, facilitating subsequent cross-linking reactions. Citric acid (CA) and sodium trimetaphosphate (STMP) synergistically constructed a dense molecular cross-linked network through esterification and phosphorylation, respectively. With the assistance of plasticizers, the tensile strength of the film increased by 62.3%, and the elongation at break reached 348.7%. Thermogravimetric analysis (TGA) confirmed that dual cross-linking significantly enhanced thermal stability. Differential scanning calorimetry (DSC) revealed a reduced glass transition temperature (Tg), indicating improved thermoplasticity. X-ray diffraction (XRD) demonstrated that cross-linking effectively disrupted the crystalline structure of starch, forming a stable amorphous network.