Chemical Modification of Polysaccharides Using Reactive Extrusion

Sodium carboxymethyl starch (CMS) was prepared using an extruder as a continuous solvent-less chemical reactor. The effects of NaOH, H2O, temperature, ethanol, sodium mono chloro acetate (SMCA), sodium tripolyphosphate (STPP), citric acid, epichlorohydrin and screw configuration on the degree of substitution (DS) and swelling properties of CMS were studied. Using these factors, CMS with the DS required for pharmaceutical disintegrant applications (0.22-0.35) was prepared. By modifying the water/ethanol ratio in the formulations and by avoiding excess gelatinization caused by using NaOH solution, CMS with rapid swelling properties in an aqueous medium, essential for super-disintegrant applications in solid dosage forms, was obtained. Both corn and potato starches were used for preparing CMS. The carboxymethyl starch, with rapid swelling properties, was characterized using Fourier-transform infrared spectroscopy and scanning electron microscopy.