The effects of ambient temperature on the compaction of pharmaceutical powders

This article presents an experimental study of the effects of raised ambient temperature in dies and punches on the compaction of pharmaceutical powders. The experiments use an instrumented hydraulic press having a temperature-controlled enclosure allowing the ambient temperature of die and punch to be varied from 20 to 57 8C. A pharmaceutical powder was compacted at temperatures in this range and mechanical parameters, such as stress transfer ratio, stress transmission ratio, and die-wall friction, were analysed to examine the effects of heat transfer between tools and powder. In particular, it is shown that increasing the environmental temperature of die and punch increases the transfer ratio and the die-wall friction. The radial pressure is also slightly increased at the first stages of the compaction. However, the stress transmission is reduced by increasing the temperature. This may indicate an increase of shear stress. It is also observed that the particles undergoing compaction are ‘softened’ by increase of the temperature. This softening is certainly due to rise in temperature of the powder generated by the compaction and by the heat flux transfer between the die and the tablet. It is suggested that these effects could be important in industrial tablet production installations without air conditioning and thus subject to variations in ambient temperature.