Optimization of Esterified Chestnut Starch Synthesis Using Response Surface Methodology and Its Application to Biodegradable Materials

Green food packaging materials with the advantages of facile degradation and sustainable recycling are widely used, among which biodegradable materials made from starch are attracting increasing attention, and increasing the hydrophobicity of starch plays an important role in improving the comprehensive performance of starch‐based materials. In this study, esterified chestnut starch (ECS) has been prepared via ultrasonication and citric acid esterification of chestnut starch (CS), and the process conditions were optimized using response surface analysis. The optimum process conditions were: Reaction time, 5.2 h; citric acid dosage, 31%; reaction temperature, 132°C; and the highest degree of substitution (DS) of ECS, 0.329. Fourier transform infrared (FTIR) spectroscopy and x‐ray photoelectron spectroscopy (XPS) have shown that the ‐COOH group of citric acid was esterified by the ‐OH group of CS. x‐ray diffraction (XRD) showed that the crystalline morphology of starch changes after ultrasonication and esterification. Scanning electron microscopy (SEM) showed that the surface of the starch granules of ECS after ultrasonication and esterification became roughened and ruptured. The thermal stability of ECS with the highest DS decreased slightly and the hydrophobic contact angle reached 108.04°. The prepared ECS was added to thermoplastic starch to prepare starch film materials and their related physicochemical properties were investigated. When ECS (DS = 0.329) was added to thermoplastic starch at 40 wt%, the resulting film exhibited optimal light transmittance, peak tensile strength (TS), superior stability, and enhanced water resistance. These properties provide a new option for the application of starch in biodegradable materials.