The effect of rate of force application on the properties of microcrystalline cellulose and dibasic calcium phosphate mixtures

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The effect of rate of force application over the range 24-1100 mm/s on the compaction characteristics of various combinations of a microcrystalline cellulose (MCC) and dibasic-calcium phosphate dihydrate (DCP) have been studied using mean yield pressure, extent of particle rearrangement ( D b ) obtained from Heckel analysis, tablet radial tensile strength and elastic recovery as the basis of the investigation. A simple relationship was observed with increasing mass fraction of MCC on mean yield pressure and elastic recovery of the compacts. At all rates of force application, mean yield pressure decreased while elastic recovery increased with increasing mass fraction of MCC, ascribed to the dominating effect of plastic deformation of the microcrystalline cellulose. No simple relationship was observed with properties such as extent of particle rearrangement ( D b ) and tensile strength. In some cases the properties of some mixtures were greater than or less than either of the two pure components. At all rates of force application, 25% w/w of MCC and 75% w/w DCP resulted in peak values for D b , which can be ascribed to a decrease in frictional and cohesive forces between particles. Higher concentrations of MCC resulted in a decrease in D b due to adhesion of the particles, which reduces the extent of particle slippage and rearrangement towards a minimum between 75 and 100% w/w MCC. The tensile strength of the mixtures decreased with increasing rate of force application. Increasing levels of MCC increased tensile strength and a plateau was obtained at 50–75% w/w MCC at all rates. 75% w/w MCC produced tablets with higher tensile strength than the individual materials respectively, due to extensive fragmentation of DCP which enhanced the filling of void spaces during compression leading to optimum force utilization, improved consolidation and better bonding of MCC. It appears from this study that a mixture of 25% w/w DCP and 75% w/w MCC may have advantages over the individual materials.