Synthetic Technics of Starch Phosphate with Mechanically Activated Cassava Starch

Starch is a morphologically complex polymer substance which consists of loose amorphous regions interspersing with highly regular crystalline regions, therefore it is difficult for the phosphate to contact with the inner molecules of the starch, which will result in low starch activity, low reaction efficiency and producing starch phosphate with low degree substitution (DS) for the esterification reaction of the starch. In this work, the starch phosphate was synthesized by dry process, during which, a customized stirring-type ball mill was used to mechanically activate the cassava starch, the orthophosphate and the urea were used separately as esterifying agent and as catalyst. The effects of activation time, reaction temperature and time, the amount of urea and phosphate used and the pH value on the degree of substitution and reaction efficiency (RE) were investigated. The suitable reaction conditions were obtained as follows: activation time of 1.5 h, amount of phosphate of 12%, pH value of 4.5, reaction temperature of 150℃, reaction time of 2 h and amount of urea of 2%. The results indicate that the mechanical activation considerably enhances the chemical reactivity of the starch, and hence promotes the DS and RE of the cassava starch phosphate. Using above suitable reaction conditions, the DS and RE of the starch phosphate prepared can reach 0.0900 and 0.933, respectively.