Transport of water and gases through EVA copolymer films, EVA(70)/PVC, andEVA(70)/PVC/gluten blends

The transport of water vapor and gases (oxygen or carbon dioxide) through p oly(ethylene-co-vinyl acetate) (EVA) films of different VA contents and thr ough EVA(70)/PVC and EVA(70)/PVC/gluten blend films, was analysed by permea tion measurements. In the case of water, a plasticization effect on the mat erial is observed for EVA films with more than 33% wt. of VA content and al so for the EVA70/PVC blend,. For EVA of 19 wt.% VA, there is no plasticizat ion, 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. Th e increase in water sorption extent with the VA content leads to a steady i ncrease 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 reduc ed (6 times).