The hydroxypropylation of starch in a self-wiping twin screw extruder

Potato starch was chemically modified in an APV self‐wiping twin screw extruder to produce hydroxypropylated starch. The product obtained had a molar degree of substitution (MS) between 0.06 and 0.26. The selectivity of the hydroxypropylation reaction varied between 50 and 95%, yields varied between 15 and 95%, and conversions between 30 and 91%. Using viscosity data of native and hydroxypropylated starch, together with extruder parameters like temperatures, residence time distribution, and shear rates, a model was set up to predict the MS values, conversions, and selectivities. With this model, interactions between temperature, reaction, and viscosity can be understood and predicted. © 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 56–68, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10034