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The objective of this dissertation was to study the use of reactive extrusion for the chemical modifications of starch and cellulose. A carboxymethyl derivative of starch and carboxymethyl and acetate derivatives of cellulose were prepared using reactive extrusion.
Carboxymethyl starch with rapid swelling properties in water was prepared using reactive extrusion. This was achieved by controlling the gelatinization and through the use of NaOH by controlling the water/ethanol ratio. The effects of NaOH, H2O, temperature, ethanol, sodium mono chloro acetate, sodium tripolyphosphate, citric acid, epichlorohydrin and extruder screw configuration on the degree of substitution of carboxymethyl starch were studied.
The physical, chemical and morphological properties of sodium starch glycolate (cross-linked carboxymethyl starch) prepared using reactive extrusion were characterized and compared with those of VIVASTAR®P. The liquid (water and 0.1N HCl) uptakes by sodium starch glycolate prepared using reactive extrusion were lower than those by VIVASTAR®P. This may have been because of gelatinization of starch and insufficient cross-linking in sodium starch glycolate prepared using reactive extrusion. Carboxymethyl starches with high degrees of substitutions also were prepared using reactive extrusion. The effects of SMCA:starch ratio, aqueous ethanol:(starch+SMCA) and the extruder screw configuration on the degree of substitution and reaction efficiency were studied.
Further, the use of reactive extrusion for the chemical modification of a non-thermoplastic material like cellulose was demonstrated. The effects of water:ethanol ratio and amounts of NaOH used, on the degree of substitution, degree of crystallinity, cellulose-II crystalline fraction, saline uptake, saline absorption and surface morphology were studied. X-ray diffraction analysis revealed that carboxymethyl cellulose prepared using 100% H2O had higher degree of crystallinty and cellulose-II crystalline fraction. Saline uptake by this carboxymethyl cellulose was comparable with that of sodium polyacrylate.
Acetate derivatives of cellulose also were prepared by a solvent-less reactive extrusion process with the use of iodine catalyst. The effects of the acetic anhydride:cellulose ratio and iodine concentration on the degree of substitution, crystalline structure, oligomer formations and surface microstructure were studied.