Effect of Ultrasonic Field on Synthesis and Characterization of Starch Acetate

The synthesis of corn starch acetate made by traditional chemical modification technology of starch in continuous ultrasonic field was investigated in this experiment. This study mainly focuses on the effects of ultrasound wave power, frequency, reaction time and amount of reactants on degree of substitution of starch acetate. The structure of the product was characterized by scanning electronic microscope(SEM), polarizing microscope, X-ray diffraction and infrared spectrum. The results show that the degree of substitution(DS) of the product is influenced by the power and frequency of ultrasound waves, the reaction time and the amount of reactants. The effect of the ultrasonic power is the most significant. The optimal condition was power 250W, frequency 60kHz, reaction time 75min and the amount of esterifying agent 20ml. The degree of substitution of the starch acetate under such conditions was 0.1043. The appearances and crystal structure of the synthetic starch acetate particles changed under the effect of ultrasonic field. There were concavities and cracks on the surface of the particles and the crystal structure were damaged resulting in lower degree of crystallinity. Infrared spectrum analysis showed that although acetyl groups are introduced into the molecules of starch , the basic structure of the starch molecules were not affected by the ultrasound waves.