The effect of particle size and viscosity grade on the compaction properties of hydroxypropylmethylcellulose 2208

Abstract

The influence of particle size and viscosity grade of hydroxypropylmethylcellulose 2208 (HPMC) on the tensile strength, compressibility, energies involved during consolidation, mean yield pressure and elastic recovery of HPMC compacts have been determined. The relationship between particle size, tensile strength and the viscosity grade of HPMC was complex. At smaller particle sizes (< 45 and 45–125 μm), an increase in the viscosity grade of HPMC resulted in a reduction in the tensile strength of its compacts. However, at larger particle sizes (125–180, 180–250 or 250–350 ũm), the tensile strength of HPMC compacts decreased with an increase in viscosity grade up to HPMC K15M, but for HPMC K100M there was a small increase in tensile strength. The compressibility indices of HPMC K100, HPMC K4M, HPMC K15M and HPMC K100M increased 58%, 74%, 49% and 70%, respectively, as the particle size was reduced from 250–350 υm to < 45 μm. This indicates that the interparticle frictional and cohesive forces increased with decreasing particle size. The tensile strength of compacts made of the smallest particle size (< 45 μm) fraction at each viscosity grade were at least three times more than the tensile strengths of compacts made of 250–350 μm. Particle size was the single most important factor in controlling the tensile strengths of HPMC tablets. The mean yield pressure to induce plastic deformation calculated from the slopes of Heckel plots was the lowest for HPMC K100. Increase in particle size resulted in an increase in elastic recovery, presumably due to a reduction in the number of particle-particle interaction points during compaction, and in a reduction of the plastic energy for all the samples. The viscosity grade of HPMC had no effect on the elastic energy. Particle size, however, did significantly affect the elastic energy of HPMC K4M and HPMC K100M.