Effects of acetic acid/acetic anhydride ratios on the properties of corn starch acetates

摘要

Corn starch was pre-treated with acetic acid and then acetylated by acetic anhydride under microwave irradiation. The effects of molar ratios of these two reagents on the acetylation of starch were investi-gated. Starch acetate with a high degree of substitution (DS, 2.93) was obtained at a molar ratio (acetic acid/acetic anhydride) of 1:1. However, the DS should tend to decrease with a change of this ratio. The FT-IR analysis indicated characteristic absorption peaks, with increasing DS materialised by an increase of the carbonyl C=O group and a decrease of the hydroxyl O-H group, at about 1750 cm~(-1) and 3450 cm"1, respectively. The X-ray diffraction patterns of acetylated starch showed an amorphous struc-ture. Degree of crystallinity, surface morphology, water solubility and water absorption index of corn starch were also affected by the changes in reagent ratios. The glass transition (T_g) and melting (T_m) tem-peratures of acetylated starches also decreased after acetylation.