Study On Synthesis Of Starch Phosphate Ester And Its Reaction Mechanism

Starch phosphate ester is one kind of starch derivative produced from esterification of starch and phosphate. It belongs to the second generation of modified starches. Starch phosphate ester which is being applied usually has lower combined phosphorus content, or lower degree of substitution and lower accessional value. Now it is applied in the fields of newspaper and food industry with high demands and required to have a higher combined phosphorus content. So the studies on synthesis of starch phosphate ester and its reaction mechanism would become more and more important and widen their perspective application.In this experiment, cassava starches manufactured from Mingyang Starch Plant were used as raw material to synthesize starch phosphate ester by esterification with sodium phosphate, sodium tripolyphosphate and mixed phosphate. The effect of reaction temperature and time, the amount of urea, pH value and the amount of phosphates on esterification was investigated and the principle of esterification process was discussed. Base on above results,we can find out the best technical conditions to synthesize starch phosphate ester containing higher combined phosphorus by orthogonal experiment. The half-dry production method was adopted to compound starch phosphate ester and Spectrophotography was adopted to analyze produt's degree of substitution. At last, the best technical conditions to prepare starch phosphate ester with sodium phosphates was determined that the reaction temperature is 160癈, reaction time 2h, amount of urea 9%, pH 5.6, amount of phosphate 8%; The best conditions to prepare starch phosphate ester with sodium tripolyphosphate is that the reaction temperature is 155, reaction time Ih, amount of urea 2%, pH5.0, amount of phosphate 4%; The best conditions to prepare starch phosphate ester with mix phosphates (NaH2PO4:Na2HPO4=l:l, mass proportion) is that the reaction temperature is 155, reaction time 2h, amount of urea 5%, pH5.4, amount of phosphate 10%. When reaction conditions were about same, the degree of substitution of starch phosphate ester synthesized with sodium tripolyphosphate was higher than that with other phosphates. Phosphorylation process of starch is complicated. It's generally think that each inorganic phosphate react with starches by means of sodium pyraphosphates which compound with -OH group of starch to synthesize starch phosphate ester by heated in high temperature. Infrared spectrogram of starch phosphate esters indicates that they still keep crystal structure of starch after esterification. Which proves that esterification mostly happens in amorphism areas of starch and little happens in its crystal areas.