Evaluation and simultaneous optimization of some pellets characteristics using a 3(3) factorial design and the desirability function.

A 3(3) full factorial design study has been employed in order to investigate the effect of three variables on size, size distribution and three shape parameters, namely roundness, elongation and e(R), of pellets prepared in a fluid bed rotor granulator with the wet granulation technique. The first variable was a formulation variable, the % w/w content of microcrystalline cellulose (MCC) and the other two variables were processing variables, the temperature of inlet air and the spray rate of the granulation liquid. The analysis of variance showed that the three variables had a significant effect (P<0.05) on pellet size and the shape factors, while only the spray rate influenced the particle size distribution. Significant interactions between the factors, for the size and the shape, were also found. The multiple regression analysis of the results led to equations that adequately describe the influence of the independent variables on the selected responses. Furthermore, the desirability function was employed in order to optimize the process under study. It was found that the optimum values of the responses could be obtained at the low levels of the % w/w content of MCC and temperature of inlet air and at the high level of the spray rate.