The application of non-contact laser profilometry to the determination of permanent structural changes induced by compaction of pellets

Abstract

Pellets of different mechanical properties were produced by extrusion and spheronisation process based on various composition (microcrystalline cellulose (MCC), lactose, glyceryl monostearate (GMS), water, ethanol and glycerol). Six hundred milligrams of these pellets were compacted at two different pressures (86.7 and 130MPa) to form flat-faced tablets and stored for 48h in ambient temperature and humidity after which their permanent structural change (plastic deformation) was investigated in terms of surface roughness parameters of both faces of the tablets, using a non-contact laser profilometer. The results were compared with the deformability values obtained from the force/displacement curve as well as the phase angle values obtained from the dynamic scan of a dynamic mechanical analyser. The increase in deformability of the pellets with the increase in porosity, increase in the contents of GMS, lactose or ethanol in the formulations and increase in compaction pressure was illustrated by the reduction of the surface roughness parameters. Analysis of variance identified the significant difference in the mean rugosity values of the tablets from the various formulations, tablet faces and compaction pressures. The deformability values obtained were reasonably comparable to those plasticity values obtained in terms of phase angle from the dynamic scan of the DMA and the force/displacement curves. The laser profilometry technique in conjunction with scanning electro-microscopy (SEM) demonstrated the low and broad based wavelike structure of the pellets after compaction rather than spiky sharp protrusions. This confirms the capability of determining the plastic deformability of the pellets from the surface roughness parameters obtained from non-contact laser profilometry.