Polyethylene glycol and dicalcium phosphate mixtures: Effect of tableting pressure

The effect of compression pressure on Polyethylene glycol 10 000 (PEG): Dicalcium phosphate (DCP) mixtures has been evaluated. The tensile strength increased with PEG content exhibiting a maxima between 40 and 80% w/w PEG depending on the compression pressure. Similar strengths could be obtained using lower pressures however higher amounts of PEG was required. PEG densified rapidly and increasing the pressure above 82 MPa has no effect on plastic energy whilst only a small increase in tensile strength was observed. Above 82 MPa, asperity melting probably occurred. DCP expended less energy in tablet expansion than PEG or their mixtures, whilst at higher pressures the plastic energy for DCP was the greatest. However the tensile strength of DCP was smaller than that of PEG and their mixtures at any compression pressure. At higher pressure, extensive fragmentation of DCP occurred and a large number of contact points were created. Although the area of contact was greater, the amount of energy involved for bonding on each contact point was smaller and consequently the bonds formed between particles were weak and the compact has low strength. The tablets containing 80% PEG:20% DCP produced the best tablets, consuming the smallest energy while producing tablets that were mechanically tough. This study showed that mixtures of a brittle material (DCP) and a plastic material (PEG) produced tablets with higher tensile strengths than those made from the pure materials alone.