The effect of temperature on the plasto-elasticity of some pharmaceutical powders and on the tensile strengths of their tablets.

Measurements have been made of the stress relaxation (SR) during, and of the elastic recovery (ER) after, compression of four directly compressible excipients, and of chloroquine diphosphate and of a paracetamol tablet formulation at temperatures between -10 and +65 degrees C and of the tensile strengths of the tablets produced. It was found that at a fixed packing fraction, the stress relaxation and tensile strength of all the materials increased and the ratio ER/SR decreased as the compression temperature was raised. Tensile strength was inversely proportional to ER/SR at all the temperatures studied. Values for the activation energies (Eo) of bonding between particles for all the materials were derived from plots of the log of tensile strength and of log SR/ER versus the reciprocal of the absolute temperature. The values of Eo obtained from the latter plots tended to be higher than from the former by a factor of between 1.5 and 4.5.