Synthesis, optimization and characterization of acetylated corn starch with the high degree of substitution.

Acetylated corn starch (ACS) was synthesized by the reaction of native corn starch (NCS) with acetic anhydride (AA) and acetic acid in an aqueous medium in the presence of p-toluenesulfonic acid (PTSA) as a catalyst. The factors that could affect the degree of substitution (DS) of corn starch were investigated which included the reaction temperature and time, the volume ratio of AA to acetic acid and the usage of the catalyst PTSA. The optimal DS of 2.85 was obtained. Fourier transform infrared (FTIR) spectrometry showed new bands at 1733, 1375 and 1252cm(-1). As DS increased, the bands at 3400cm(-1) and 1083cm(-1) were gradually weakened. The scanning electron microscopy (SEM) of the ACS indicated that the exterior and interior of native starch were destroyed by the esterification. Wide angle X-ray diffraction revealed that the peaks at 15°, 18°, 20° and 23° were diminished, while the peak at 21° became more distinct as the DS increased. Differential scanning calorimetry (DSC) thermograms exhibited that ACS had some lower gelatinization temperatures and enthalpies than NCS.