Influence of methylparaben as a solid-state plasticizer on the physicochemical properties of Eudragit® RS PO hot-melt extrudates

The purpose of this study was to investigate the properties of methylparaben as a solid-state plasticizer for Eudragit(R) RS PO during a hot-melt extrusion process. Extruded matrices containing different levels of methylparaben and Eudragit(R) RS PO, were prepared by feeding the powder blend through a hot melt extruder. The melt viscosity of the polymer blends was assessed by torque rheometry using a Brabender Plasticorder. The physicochemical properties of the extruded methylparaben-containing polymer matrix were characterized by differential scanning calorimetry and X-ray diffraction. Solid state nuclear magnetic resonance spectroscopy (NMR) was used to study the possible interaction between methylparaben and Eudragit(R) RS PO polymer. The results demonstrated that the glass transition temperature of the Eudragit(R) RS PO decreased with increasing levels of methylparaben in the extrudate, due to an increase in the chain mobility of Eudragit(R) RS PO. The crystallinity of methylparaben was absent following hot-melt processing. At increasing levels of methylparaben in the extrudates, a decrease in the melt viscosity was seen due to a plasticization of the polymer. Rheological properties of the extrudates containing methylparaben were compared with the extrudates containing conventional plasticizers. It was found that methylparaben was as effective as triethyl citrate (TEC) in reducing torque during the extrusion process. Solid state NMR spectra indicated a change in the chemical shift of Eudragit(R) RS PO plasticized with methylparaben, which could be ascribed to an interaction between the hydroxyl group of the methylparaben and the ester group of the Eudragit(R) RS PO polymer. The results of this study demonstrated that methylparaben could be used as a solid-state plasticizer for the Eudragit(R) RS PO polymer when a hot melt extrusion technique was employed in the preparation of sustained release tablets. (C) 2003 Elsevier Science B.V. All rights reserved.