INFLUENCE OF PLASTICIZERS ON THE MECHANICAL-PROPERTIES OF PELLETS CONTAINING EUDRAGIT(R)-RS-30-D

The influence of plasticizers on the mechanical properties of single p ellets containing the acrylic polymeric dispersion, Eudragit(R) RS 30 D, as a granulating binder was investigated. Microcrystalline cellulos e and anhydrous lactose were used as the substrate powders for pellets prepared by the wet massing and extrusion/spheronization technique. T he effects of hydrophilic and hydrophobic plasticizers on the mechanic al properties of the pellets and thermal properties of free films were investigated. The mechanical properties, including tensile strength a nd Young's modulus, of individual pellets were determined by a diametr al compression method with a Chatillon(R) tension/compression apparatu s. The results demonstrated that both the tensile strength and Young's modulus of the pellets decreased as the plasticizer content increased in the pellet formulation, with the exception at low plasticizer leve ls. The influence of plasticization on the granulating polymer was ref lected in the mechanical properties of pellets, indicating that the pe llets underwent a cohesive fracture. The unexpected increase in the te nsile strength and Young's modulus of the pellets containing low level s of plasticizers was ascribed to the antiplasticization of the polyme r due to the immobilization of the polymer molecules by hydrogen bondi ng, van der Waal's forces and steric hindrance from the plasticizer mo lecules. Pellets containing low levels of plasticizers exhibited a bri ttle fracture behavior under compression while a ductile property was observed at higher plasticizer concentrations. The transition of the f racture behavior from a brittle to a ductile pattern was found to take place when plasticizer levels in the acrylic polymer were between 10 and 20% based on the weight of dry polymer. The transition was due to the shift of the polymeric binder from a glassy to a rubbery state, wh ich was verified by the glass transition temperature values of the fre e films. (C) 1997 Elsevier Science B.V.