The effect of some formulation variables on crack propagation in pigmented tablet film coatings using computer simulation

Abstract

A model originally developed to simulate crack propagation in structural steel and recently shown to he applicable to pigmented tablet film coatings has been used to study the effect on crack propagation of some specific formulation variables such as the addition of plasticizers to the polymer, the use of higher molecular weight polymer, the addition of a second population of a pigment of larger particle size and the breadth of the particle size distribution of the pigment. Simulations investigating plasticizer addition and the effect of polymer molecular weight confirm that both would be beneficial in alleviating the problems of cracking as found in practice although in the former the mechanism operates by increasing the critical strain energy release rate rather than increasing the critical stress intensity factor of the system. The addition of a second population of a pigment of larger particle size and the broadening of the size distribution of the pigment both result in a decrease in crack velocity thus providing an alternative. although as yet unproven, method for alleviating cracking. The program is easy to use enabling many simulations to be performed with minimum effort.