Swellable starch ester and methods of its production and use

A method of producing a starch ester consisting of more than 50% by weight of water-insoluble components and having a retention capacity of >500% for 0.9% (by weight) aqueous NaCl solution, relative in each instance to the weight of the dry starch ester, said retention capacity being determined by allowing 0.1 g of the starch ester welded into a nylon bag with a mesh width of 52 .mu.m to swell for 30 min. in a 0.9% NaCl solution, centrifuging the bag for 5 min. at 1400 rpm, and gravimetrically determining any weight increase, said method comprising reacting starch or modified starch in a one-stage aqueous reaction with maleic anhydride or a mixture of carboxylic acid anhydrides containing maleic anhydride at a pH of 7 to 11 and a temperature of 0.degree. to 40.degree. C.;

• and maintaining the pH in the desired range by adding aqueous alkali solution with a concentration of approximately 10 to 50%.