Effect of Punch Velocity on the Compressibility and Stress Relaxation of Particles and Granules.

Abstract

Effect of punch velocity on compaction properties of particles and granules has been studied through compressibility, stress relaxation and elastic recovery. The compressibility of powders was evaluated by the modified Kawakita equation (K). The relationship between compression stress (P) and reciprocal of porosity (1/e) showed an inflection point. Denoting the slope of low compression stress in the stage of densiflcation by powder slippage and rearrangement by K1, and K2 the slope of high compression stress in the stage of elastic, plastic deformation and brittle fracture of particles and granules, the values of K1 and K2 decreased with increasing punch velocity. The diametral tensile strength had a tendency to decrease with decreasing K2, while stress relaxation increased with increasing punch velocity. In particular, constant a and b values in a cellulose system (microcrystalline cellulose) were greater than those in a non -cellulose system (a and b lactoses). As found in the relationship between constant a, b and constant K2, materials which undergo plastic deformation and fragmentation have high stress relaxation. It was also found that elastic recovery ratios of tablets increased with increasing punch velocity. Therefore punch velocity affects both the stress relaxation and elastic recovery ratio of tablets.

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