Compression characteristics of granulated materials II. Evaluation of granule fragmentation during compression by tablet permeability and porosity measurements

Abstract

Lactose was granulated with 5% (w/w) polyvinylpyrrolidone as a binder with a wet massing-screening procedure. Fourteen granulations were produced by using different amounts and types of solvent for the binder during the agglomeration procedure. After the granulation, the size fraction 500–710 μm was separated from each granulation for investigation. The granules were characterised on water and binder content, and granule porosity and friability. Both the porosity and friability of the granules were affected by the process conditions. However, there was no correlation between these parameters, which indicates that one surface property of the granule i.e., the ability to withstand attrition, can be different from the overall granule strength. The volume reduction behaviour during compaction was evaluated by measuring tablet permeability and tablet porosity as a function of compaction pressure. The results indicate that the granules became denser at low compaction pressures. It is therefore difficult to use the changes in porosity with compaction pressure as a measure of the degree of granule fragmentation during compression. The tablet permeability as a function of compaction pressure varied among the granulations which indicates that the ability to break down during compression, i.e., the granule fragmentation, varied. It is suggested that changes in tablet permeability with compaction pressure can be used as a measure of this property. The difficulty of defining the intergranular pore space in the tablet will affect the calculation of the tablet surface area. However, the results indicate that in the pressure range used for the permeametry measurements, the total porosity is probably fairly close to the intergranular pore space. Thus, it is suggested that surface area—compaction pressure profiles give a reasonable estimate of the degree of granule fragmentation during compression.