Effect of Polymer (PE-EVA-PVC) Structure on Gas Permision Properties

The effect of film preparation conditions and polymer structure on the gas permeation properties of polyethylene (PE), ethylene vinyl acetate (EVA) and Poly vinyl chloride (PVC) films is investigated. Film blowing and phase inversion methods were applied in the production of PE, EVA and PVC films, respectively. The permeations of pure oxygen and carbon dioxide gases are measured at room temperature. The results indicate that with the increase of PE film thickness, the permeability and solubility of O-2 and CO2 in these films were decreased; but the diffusivities of gases through PE film were increased. In addition, in the case of EVA copolymers, by increasing the content of vinyl acetate, the permeability of CO2 is increased. The rate of increase in CO2 permeability was different for samples having different preparation conditions. For example, the samples prepared using Chloroform as a solvent instead of THF, showed lower CO2 permeability. The morphological study of film structure indicated that the higher CO2 permeability for the samples made from THF solvent is due to the existing of higher porosity in the under layer polymer area. Also scanning electron microscopy micrographs showed that with the usage of phase inversion method, there will be a thin dense layer near to the glass substrate. Also the results for PVC films show that with the increase of polymer polarity, the permeability of CO2 will increase while the O-2 permeability does not change a lot.