The application of non-contact laser profilometry to the determination of permanent structural change induced by compaction of pellets II. Pellets dried by different techniques.

Microcrystalline (MCC) pellets of different structural and mechanical properties were produced by the process of extrusion and spheronization from the formula MCC:water:ethanol (5:3:2) using four different drying techniques, namely: freeze-drying, fluid-bed drying, hot air oven drying and desiccation with silica-gel. Six hundred milligrams of these pellets were compacted by 130 MPa to flat-faced tablets and stored for 48 h in ambient temperature and humidity after which their permanent structural change (plastic deformation) was investigated in terms of surface roughness parameters using a non-contact laser profilometer. The results were compared with the deformability values measured as a reciprocal of the slope of the force/displacement curve obtained during diametral compression test of the individual pellets. Based on the different rate of moisture removal, means of heat and mass transfer, and static and dynamic nature of the bed the different drying techniques produced pellets of different porosity, strength and deformability. The increase in deformability of the pellets with the increase of porosity 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 pellets produced by the various drying techniques. The deformability values obtained were reasonably comparable to those plasticity values explained in terms of the inverse of the slope of the force/displacement curves. The laser profilometry technique was able to quantify the permanent structural change of the pellets after compaction in terms of mean rugosity values. The methodology was able to incorporate a wide variety of deformable pellets of the same formulations but produced by different drying techniques. The porous freeze-dried pellets produced the smoothest tablet surface profile, while the other techniques increased the rugosity values in ascending order from fluid-bed drying, desiccation with silica-gel to hot air oven drying technique.