TEMPERATURE-CHANGES DURING TABLETTING MEASURED USING INFRARED THERMOVIEWER

To observe the rise in temperature during tabletting an infrared therm oviewer was used together with an instrumented eccentric tablet press. To evaluate the tabletting process, temperatures measured from surfac es of recently ejected tablets were used together with energy paramete rs. Two direct compression excipients, plastically deforming microcrys talline cellulose and fragmenting dicalcium phosphate dihydrate, were tabletted. Due to differences in specific heat values, the temperature rise of the tablets was higher with microcrystalline cellulose than w ith dicalcium phosphate. Also more non-homogeneous particle shape and plastic deformation instead of fragmentation may have led to higher te mperatures of microcrystalline cellulose tablets. For both test materi als the temperature of the tablets rose with the compressional force w hereas lubrication diminished the rise in temperature. Due to the non- homogeneous densification the highest temperature values were obtained at the centre of the upper surfaces of the tablets. After a short ini tial stabilization phase, the rise in tablet temperature became greatl y dependent on the temperature increase of the powder in the hopper. F rom the energy parameter values, derived either from force and displac ement data (mechanical energy), or from specific heat, temperature inc rease and tablet weight values (thermal energy), it was noted that the mechanical energy was very extensively converted to thermal energy. T hus, a permanent increase in energy content of powders by compression seemed to be small. The infrared thermoviewer was found to be an accur ate and informative method for evaluating changes in the temperature a nd energy content of compressed powders during a dynamic tabletting pr ocess.