Abstract: To optimize the process for the synthesis of starch acetate from corn starch, the effects of catalyst amount, the volume mixing ratio of acetic acid to acetic anhydride, and reaction time and temperature on the degree of substitution (DS) of starch were evaluation by single factor experiments, and a mathematical model describing the functional relationship between starch DS and the above four variables was set up based on a 29-run, 4-factor, 3-level response surface design coupled with multiple regression fitting. The model was subjected to analysis of variance and response surface analysis, and the results showed that the optimum conditions for the synthesis of starch acetate were as follows: catalyst amount of 0.11 mL and the mixing ratio of acetic acid to acetic anhydride of 1:1.39 by volume for a reaction period of 1.59 h at 87.61 ℃. Validation experiments indicated that the maximum substitution degree of starch acetate was 2.95 under these conditions. FTIR results indicated that the hydroxyl groups in each glucose unit of starch acetate were gradually esterified, and meanwhile the content of acetyl group became higher with the increase of substitution degree. Scanning electron microscopic (SEM) observations revealed that the surface of starch acetate was much rougher, had increased porosity and displayed cellular structure, indicating that the esterification occurred not only on the surface but also inside of starch granule.

Key words: starch acetate, synthesis process, response surface methodology, substitution degree, infrared spectroscopy, scanning electron microscope