(566g) Chemical Modification of Polysaccharides Using Reactive Extrusion

A Brabender TSE-20 co-rotating twin screw extruder was used for chemical modification of starch and cellulose. Ether and ester derivatives of the polysaccharides with various degrees of substitutions (DS) were prepared. These derivatives included carboxymethyl starch, carboxymethyl cellulose, starch acetate, starch maleate and cellulose acetate. Carboxymethyl starch, with low DS (0.3-0.4), was prepared for super-disintegrant applications as a pharmaceutical excipient. The physical, chemical, morphological and disintegrant properties of cross-linked carboxymethyl starch were compared with those of a commercial super-disintegrant VIVASTAR®P. High DS carboxymethyl starches (DS 0.68-1.54) also were prepared using the extruder. The effects of the amounts of aqueous ethanol and NaOH and screw configuration on the DS, reaction efficiency and product microstructure were investigated. Carboxymethyl cellulose also was prepared using a twin screw extruder to study the effects of water/ethanol ratio and amount of NaOH on the product DS, crystallinity, microstructure, viscosity and water absorption properties. Further, starch and cellulose esters also were prepared using reactive extrusion. Reactive extrusion for preparing these modified bio-polymers is more efficient, uses less solvents, is faster and has more complete reaction and fewer byproducts than conventional processes.