PREPARATION OF CATIONIC STARCH CONTAINING QUATERNARY AMMONIUM SUBSTITUENTS BY REACTIVE TWIN-SCREW EXTRUSION PROCESSING

Cationic starch, an important additive for papermaking and other uses, was prepared from native cornstarch and 3-chloro-2-hydroxypropyltrime thylammonium chloride in aqueous sodium hydroxide using a twin-screw e xtruder as the reactor. The effects of physical and chemical reaction variables on reaction efficiency (RE) and degree of substitution (DS) of up to 0.05 were studied. RE was based on nitrogen content contribut ed by cationization of the starch after the products were exhaustively washed to remove unreacted monomer. Under certain reaction conditions , exceptionally high RE (90%+) was achieved, exceeding maximum values previously reported using laboratory-batch reaction procedures. The co mbined effects of high reaction temperature (90 degrees C), intense mi xing, high-starch solids (65%), and appropriate levels of catalyst con tributed to the unusually high RE values achieved by the reactive extr usion process. (C) 1994 John Wiley and Sons, Inc.