AN INVESTIGATION INTO THE CAPPING OF PARACETAMOL AT INCREASING SPEEDS OF COMPRESSION

A study of the capping tendency of paracetamol using a wide range of compression speeds (24-850 mm/s) has been performed. Capping pressure, plastic energy (PE) and elastic energy (EE), EE/PE ratio, work of compaction and mean yield pressure derived from Heckel analysis were used as the basis of the investigation. The capping intensity of paracetamol was observed to increase with an increase in the speed of compression, due to the significant increase of 65.24% in the elastic energy compared to a 32.87% increase in plastic energy over the same speed range. The relatively high increase in elastic energy appears to be a more important factor than air entrapment in the capping tendency of paracetamol compacts. The work of compaction was found to increase with compression speed, ascribed to a high energy input required for elastic deformation, fragmentation of particles and formation of bonds. A good correlation was observed between the natural logarithm of compression speed and capping pressure and an equation has been proposed to describe the relationship. The critical excipient content was found to be 25% and 50% w/w of microcrystalline cellulose (MCC) at a speed of 24-300 mm/s and 500 mm/s, respectively, however incorporation of 25% dibasic calcium phosphate dihydrate (DCP)/75% w/w microcrystalline cellulose (MCC) in paracetamol formulations was found to have greater resistance to capping and produced tablets with double the tensile strength of compacts containing 25% w/w of MCC alone.