Preparation of cationic wheat starch by twin-screw reactive extrusion

Cationic starches were prepared in a corotating twin-screw extruder by using wheat starch and two different reagents: 2.3-epoxypropyltrimethylammonium chloride (Quab 151(R)) and 3-chloro 2-hydroxypropyltrimethylammonium (Quab 188(R)) in aqueous sodium hydroxide (NaOH). The different factors affecting this reaction were investigated. These factors include the extrusion conditions (feed rate, screw speed, barrel temperature), the reagent chemical structure, the starch plasticizer, and the molar ratio between Quab and NaOH. Degree of substitution (DS) and reaction efficiency (RE) were characterized, as well as starch transformation. High reaction efficiency (90%) can be reached for a low degree of substitution. It appears that the epoxy form of the reagent (Quab 151(R)) is more efficient in all processing conditions. (C) 2004 Wiley Periodicals, Inc.