Anomalous effect of compression pressure on the brittle fracture tendency of alpha-cellulose tablets.

The effect of varying the compression pressure on the brittle fracture tendency of alpha-cellulose and lactose tablets has been investigated. Tablet tensile strength, (T), packing fraction, (Pf), and brittle fracture index (BFI) were determined at different compression pressures (0.82, 1.22 and 1.63 MPa). In another aspect of the study, alpha-cellulose and tapioca powders were mixed in various proportions to obtain powders of varying plastoelasticity. Their tableting characteristics T, Pf and BFI were also determined at the different compression pressures. The polymer, alpha-cellulose displayed the characteristics of plastic compression--a low BFI but high T and Pf values while lactose displayed the characteristics of elastic compression--a high BFI but low T and Pf values. The degree of plastic compression decreased as the proportion of tapioca in the powder mixture increased from 0 to 50% w/w. Higher concentrations of tapioca >50% produced crumbly tablets at all compression pressures, thus indicating that tapioca is highly elastic. Increase in the compression pressure caused an increase in the BFI values of lactose tablets, 0.39-0.76 but a decrease in the BFI values of alpha-cellulose tablets, 0.38-0.09. This decrease became less pronounced as the plasticity of the powder mixtures decreased. The difference in the response of the tablets to the change in compression pressure relates to the difference in the plastoelasticity of the materials tested.