Temperature changes during tabletting measured using infrared thermoviewer

Abstract

To observe the rise in temperature during tabletting an infrared thermoviewer was used together with an instrumented eccentric tablet press. To evaluate the tabletting process, temperatures measured from surfaces of recently ejected tablets were used together with energy parameters. Two direct compression excipients, plastically deforming microcrystalline 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 with dicalcium phosphate. Also more non-homogeneous particle shape and plastic deformation instead of fragmentation may have led to higher temperatures of microcrystalline cellulose tablets. For both test materials the temperature of the tablets rose with the compressional force whereas 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 initial stabilization phase, the rise in tablet temperature became greatly dependent on the temperature increase of the powder in the hopper. From the energy parameter values, derived either from force and displacement data (mechanical energy), or from specific heat, temperature increase and tablet weight values (thermal energy), it was noted that the mechanical energy was very extensively converted to thermal energy. Thus, a permanent increase in energy content of powders by compression seemed to be small. The infrared thermoviewer was found to be an accurate and informative method for evaluating changes in the temperature and energy content of compressed powders during a dynamic tabletting process.