Localized cracking around pigment particles in tablet film coatings: a theoretical approach.

The problem of localized cracking around pigment particles in tablet film coatings has been treated as being analogous to stress cracking in two phase ceramics. For this purpose a simple model of a spherical cavity in an infinite isotropic medium has been used. As well as allowing the estimation of the stresses generated by the differences in thermal expansion of the dispersed pigment and the polymer matrix, the model predicts the effect of some formulation variables. The predictions are in agreement with the observed cracking on film-coated tablets.