The effect of physical aging on the dissolution rate of anionic polyelectrolytes

The effect of physical aging on the dissolution and mechanical properties of hydroxypropyl methylcellulose phthalate (HPMCP) was investigated. Dissolution rate measurements were performed on films which, initially above the glass transition temperature, Tg, were quenched to a sub-Tg storage temperature, aged at that temperature for a period of time and then quenched again to 25 degrees C. Within the time scale of observation, reductions in the dissolution rate to a limiting value were observed. HPMCP was also found to age in the same storage temperature range as determined by a creep compliance technique. These mechanical results indicate a change in glass structure and show that a limiting density was approached. Parallel changes were observed in the dissolution rate studies suggest that dissolution rate is governed in part by glass density. Therefore, mechanical changes of glassy films can yield pharmaceutically relevant information about the extent of physical aging and serve as an indicator of the effect of aging on dissolution rate.