Numerical evaluation of the capping tendency of microcrystalline cellulose tablets during a diametrical compression test.

Capping is one of the major problems that occur during the tabletting process in the pharmaceutical industry. This study provided an effective method for evaluating the capping tendency during diametrical compression test using the finite element method (FEM). In experiments, tablets of microcrystalline cellulose (MCC) were compacted with a single tabletting machine, and the capping tendency was determined by visual inspection of the tablet after a diametrical compression test. By comparing the effects of double-radius and single-radius concave punch shapes on the capping tendency, it was observed that the capping tendency of double-radius tablets occurred at a lower compaction force compared with single-radius tablets. Using FEM, we investigated the variation in plastic strain within tablets during the diametrical compression test and visualised it using the output variable actively yielding (AC YIELD) of ABAQUS. For both single-radius and double-radius tablets, a capping tendency is indicated if the variation in plastic strain was initiated from the centre of tablets, while capping does not occur if the variation began from the periphery of tablets. The compaction force estimated by the FEM analysis at which the capping tendency was observed was in reasonable agreement with the experimental results.