THE INFLUENCE OF MOISTURE-CONTENT ON THE CONSOLIDATION AND COMPACTION PROPERTIES OF PARACETAMOL

The influence of moisture content on the consolidation and compaction characteristics of paracetamol has been studied. Compression speed, mean yield pressure, relative powder density (D0), tablet crushing strength and capping pressure were used as the basis of the investigation. At all speeds of compression, mean yield pressure decreased with increasing moisture content especially up to 6% w/w, due to the plasticizing effect of moisture on the paracetamol powder. The relative density of the paracetamol tablets increased with moisture content due to interparticulate and die wall lubrication effects of the moisture forming surface films on the paracetamol particles, which smooth surface microirregularities and so reduce frictional forces and promote particle rearrangement and slippage. Increasing percentages of moisture up to 6% w/w increased tablet crushing strength, whilst higher moisture contents of 8% w/w significantly reduced compact strength. The initial increase in compact strength was likely to be due to the hydrodynamic lubrication effect of moisture, which promotes compaction force transmission and formation of strong hydrogen bonds. The subsequent decrease in tablet strength with moisture content above 6% w/w can be ascribed to hydrostatic resistance of excessive moisture in the void spaces, which reduces particle-particle contact area, surface energy and corresponding adhesive forces. The capping pressure of the paracetamol compacts increased with moisture content up to 6% w/w, probably due to the formation of strong interparticulate hydrogen bonding, which reduces particle-particle separation. The subsequent decrease in capping pressure at 8% w/w moisture content can be attributed to bond weakening as a result of the disruption of particle-particle bonds by an excess of moisture.