Abrupt disintegration of highly porous particles in early stage dissolution

Dissolution of highly porous particles is a ubiquitous process in formulation chemistry. Scientific challenges remain unsolved due to the complex of interfacial properties and physical interactions between solid, liquid and gas phases. Two spray-dried powders consisting of sodium sulphate and linear alkylbenzene sulfonate (LAS) were used to investigate the abrupt disintegration mechanism focusing on the residual air in the highly porous particle during wetting stage. Four typical dissolution phenomena were identified through individual particle dissolution experiments using optical microscopy. The images suggest for the first time a link between abrupt disintegration phenomenon and air behaviour. We have examined the hypothesis that, as well as chemical changes occurring during wetting, physical processes can lead to disintegration. Tensile tests of individual particles in both dry and hydrated conditions show significant weakening of the particle strength during hydration. Mathematical simulation shows that fast penetration of water through the open-ended pores compresses entrapped air and increases the internal pressure. Hoop stresses generated by internal pressure are of the same magnitude as breaking forces, suggesting that abrupt disintegration in the early stage of dissolution is driven by air compression.