A pregelatinized starch (PGS) was derivatized with sodium chloroacetate (SCA) in alcoholic medium under alkaline condition to produce carboxymethyl pregelatinized starch (CMPGS) with various degrees of substitution (DS). Influence of the molar ratio of SCA to the glucopyranose units (SCA/GU), reaction time, temperature and the amount of sodium hydroxide on the degree of substitution (DS) and the reaction efficiency (RE) was studied. An optimal concentration of 30% of NaOH, for a reaction time of 1 h at 50 °C and molar ratio (SCA/GU) equal to 1.0, yielded an optimal DS of 0.55 and a RE of 55%. SEM micrographs revealed that the carboxymethylation assigned the structural arrangement of CMPGS and caused the granular disintegration. Wide angle diffraction X-ray (XRD) showed that the crystallinity of starch was obviously varied after carboxymethylation. New bands in FTIR spectra at 1417 and 1603 cm(-1) indicated the presence of carboxymethyl groups. The solubility and viscosity of CMPGS increased with an increase in the degree of modification. In order to investigate the influence of DS on physical and drug release properties, CMPGS obtained with DS in the range of 0.12-0.55 was evaluated as tablet excipient for sustained drug release. Dissolution tests performed in phosphate buffer (pH 6.8), with Ibuprofen as drug model (25% loading) showed that CMPGS seems suitable to be used as sustained release excipient since the drug release was driven over a period up to 8 h. The in vitro release kinetics studies revealed that all formulations fit well with Korsmeyer-Peppas model and the mechanism of drug release is non-Fickian diffusion.
Keywords: Carboxymethylation; Degree of substitution; Monolithic tablet; Powder characterization; Pregelatinized starch; Sustained release.