A theoretical and experimental study of additive effects of physical aging and antiplasticization on the water permeability of polymer film coatings.

The effects of physical aging and antiplasticization on the water transport properties of glassy cellulose acetate film-coated tablets were investigated. The gradual approach toward thermodynamic equilibrium during physical aging decrease the free volume of the polymers. This decrease in free volume is accompanied by a decrease in the transport mobility, with concomitant changes in those properties of the polymer that depend on it. Antiplasticization arises from an interaction between the polymer and the plasticizer molecules and decreases the molecular mobility of the polymer and plasticizer. This effect was confirmed by mechanical measurements of polymer free films at the same experimental temperature. We have studied the additive effect of aging and antiplasticizing to see if the individual effects would interfere with one another, as might be expected if the same free volume were involved in each. The pronouncedly additive effects of physical aging and antiplasticization on the water permeability can be found in cellulose acetate film-coated tablets that were affected by longer physical aging time and lower plasticizer concentration. A theoretical study suggested that the free volume in the glassy polymer should consist of at least two independent parts, one of which is affected by annealing and the other by antiplasticization.