Transport of water and gases through EVA copolymer films, EVA70/PVC, and EVA70/PVC/gluten blends

The transport of water vapor and gases (oxygen or carbon dioxide) through poly(ethylene-co-vinyl acetate) (EVA) films of different VA contents and through EVA(70)/PVC and EVA(70)/PVC/gluten blend films, was analysed by permeation measurements. In the case of water, a plasticization effect on the material is observed for EVA films with more than 33% wt. of VA content and also for the EVA70/PVC blend,. For EVA of 19 wt.% VA, there is no plasticization, while for LDPE (low density polyethylene) and EVA of 4.5 wt.% VA, the water diffusion coefficient decreases with increasing the water content. A negative plasticization effect was accounted for by an empirical model and attributed to the formation of water clusters in the non polar polymers. The increase in water sorption extent with the VA content leads to a steady increase in the water permeability in the EVA copolymers while for the EVA70/PVC blend, the reduced water permeability is explained by the interaction between chlorinated units and polar groups. In the case of gas permeation, both for O-2 and CO2 and whatever the VA content of the copolymer used, the experimental curves are characterized by a constant diffusion coefficient. This result is not surprising as it is generally admitted that, gases sorb into rubbery polymers according to Henry's law. By mixing PVC with the EVA of 70% wt. VA, the diffusion coefficients Of CO2 and O-2 are greatly reduced (6 times).