Optimization of cassava starch acetate synthesis using response surface methodology and microstructural evaluation for enhanced hydrophobic properties

• Cassava starch acetylation optimized using Response Surface Methodology. • High substitution degree (DS = 1.68) achieved under mild reaction conditions. • Acetylation improved film hydrophobicity with contact angles > 100°. • Flexibility and moisture resistance of TPS films significantly enhanced. • Eco-friendly and scalable process for biodegradable packaging materials. Cassava starch was successfully acetylated via a simplified and scalable process to enhance its hydrophobicity, targeting applications in biodegradable food packaging. Process optimization was carried out using single-factor experiments in combination with Response Surface Methodology (RSM), focusing on the effects of the acetic anhydride-to-starch (AAD/S) ratio, NaOH concentration, and acetic acid-to-acetic anhydride (AA/AAD) ratio. The optimized process yielded a high degree of substitution (DS = 1.69) at an AAD/S ratio of 3.73, an AA/AAD ratio of 0.455, and a NaOH concentration of 0.193 mL/g starch. Structural and functional characterization through FTIR, SEM, XRD, and TGA confirmed successful acetylation and indicated substantial modifications in morphology, crystallinity, and thermal behavior. The cassava starch acetate (CSA) obtained in this study has been proved to be a suitable base material for TPS films. The prepared TPS films exhibited smooth and even surfaces. The hydrophobic character increased, with water contact angles >100°. The material had high flexibility, stretching at break from 10% to 500%, that depended on degree of substitution. These findings verify that the acetylation increased molecular mobility and compatibility in the starch matrix, thereby producing flexible and moisture-resistant films for biodegradable packaging items. Therefore, the optimized conditions of acetylation are an ecologic and high effective method for preparing cassava starch acetate with great potential in sustainable/biodegradable packaging material.