Studies of Starch Esterification: Reactions with Alkenylsuccinates in Aqueous Slurry Systems

Starch esters prepared by modifications with hydrophobic alkenyl succinic anhydrides provide an opportunity to regulate the hydrophobic characteristics of these products. This is of great interest since many potential applications of modified starch products exploit their amphiphilic character. The objective of this work was to develop a greater understanding of how the reaction parameters in aqueous slurry reactions affect the efficiency of starch modification with dodecenyl succinic anhydride (DDSA). A systematic study was performed to determine how changes in the starch concentration, starch/anhydride ratio, pH, temperature, and reaction time affect the efficiency of esterification. Surprisingly, variations in the starch concentration (25 to 65 % w/w relative to water) at a 10 % anhydride concentration (w/w relative to starch) caused little change in the reaction efficiency. Maintaining the reaction within a pH range of 8.5–9.0 and at a temperature between 22 and 27 °C was preferred. The reaction efficiency decreased as the ratio of anhydride to starch increased. Also, extending the reactions beyond 48 h resulted in products of lower substitution. After a set of preferred reactions conditions were established, a comparison of reaction efficiencies as a function of the n-alkenyl chain length of the anhydrides used was performed. As the alkenyl chain length increased from 8 to 18 carbons a substantial decrease in the reaction efficiency occurred.