No abstract

Severalworkers have investigated the plastic behaviour of pharmaceutical materials by following the stress relaxation of compressed tablets. However, most studies have been of single materials and many studies neglect the stress relaxation at short o r long times. The 90-125pm sieve fractions of materials shown in Table 1 were conditioned at 43% r.h., 2OoC before use. Sufficient powder to give tablets 3mm thick at zero porosity was compressed in a 12mm diameter plane-faced punch and lubricated die set using a Caleva COMP2500. The powder was compressed at a strain rate of lmmlmin. to maximum upper punch pressures of 75MPa or 162.5MPa and the decay in stress followed for 1200 seconds. Five tablets of each sample were compressed and the results averaged and corrected f o r relaxation of the apparatus. The results were analysed using several methods (e.g. David & Augsburger 1977;Hiestand 1972; Shott 1983). Qualitatively similar results were obtained whichever method was used but none was found to linearise the data over the full timescale. The results were therefore expressed simply as a percentage of the maximum upper punch pressure at various times.