Compaction studies on pellets: II. Coated pellets

Abstract

Compaction characteristics of Surelease coated pellets were studied using several techniques including porosity change, Heckel equation, total work of compaction and elastic recovery indices. The reduction in yield strength and an increase in tensile strength of the compacts caused by the addition of a Surelease coating to the pellets is ascribed to the interlocking forces between the substrate and the coating and to the development of additional bonds formed by plastic deformation of the coating during compaction. However, increasing amounts of the coating on the pellets reduced their yield strengths and resulted in compacts with lower tensile strength and higher elastic recovery values. The effect of the rate of load application on the compaction characteristics of Surelease coated pellets was also studied. As the punch velocity increased there was a reduction in the tensile strength values of the compacts and an increase in both yield pressure and elastic recovery values. The change in the magnitude of these values with the rate of load application was greater for the compacts made from pellets coated with increasing amounts of Surelease. A nonlinear optimization technique was also employed to further investigate the effect of rate of load application on the coated pellets. Pellets coated with increasing amounts of coating exhibited relatively more punch velocity dependence. Dissolution studies revealed that coated pellets lost their sustained release characteristics on compaction due to formation of cracks within the coating and to the fragmentary/elastic nature of the pellets.