Preparation of some starch ethers using the semi-dry state process

Two types of starch ethers have been prepared using a semi-dry process. These starch ethers are cyanoethylated and carbamoylethylated starch. The different factors affecting the preparation of these ethers have been studied. These factors include mode of adding the different ingredients, reaction medium, sodium hydroxide/anhydroglucose unit molar ratio, monomer concentration, reaction temperature and duration. The extent of etherification and the etherification reaction efficiency (ERE) were traced by estimating nitrogen content, carboxyl and total ether contents. Comparison of the ERE on using the semi-dry state and the wet state processes indicates the privilege of the former. The highest degrees of substitution (DS) values obtained were 0.66 and 0.52 of carbamoylethylated and cyanoethylated starch samples, respectively, within the studied range. Conditions are described giving high DS at reaction times short enough to keep hydrolysis of polymer bound nitrile and amide groups low. At longer reaction times, the major side reaction during carbamoylethylation is hydrolysis and during cyanoethylation deetherification. (C) 2001 Elsevier Science Ltd. All rights reserved.