TRANSPORT MECHANISMS OF GASES IN ANNEALED LINEAR LOW-DENSITY POLYETHYLENE FILMS

The effect of the pressure difference on the permeability of carbon di oxide, oxygen, and nitrogen through annealed LLDPE films is studied. T he isotherms showing the dependence of the permeability coefficient on the pressure of the upstream chamber, p(o,) exhibit an anomalous decr ease in the low-pressure region whose location is shifted to lower val ues of p(o) as the temperature of the isotherms decreases. The diffusi on coefficient increases with p(o), the increase being larger the high er is the temperature. The curves showing the dependence of the solubi lity coefficient on the pressure of the upstream chamber exhibits the same pattern as that of the permeability coefficient. The strong depen dence of the diffusive characteristics of gases on p(o) in the low-pre ssure region was interpreted in terms of the dual mode theory. The val ues of the apparent diffusion coefficients for the molecules in the di ssolved and the trapped modes are estimated. In the same way, the Henr y's law solubility coefficient, k(D), and the Langmuir sorption capaci ty, C'(H), are obtained. The values of k(D) and C'(H) for different ga ses are somewhat lower than those reported for glassy membranes. A det ailed study on the effect of p(o), on the activation energies associat ed with both the permeability and the diffusion coefficients is report ed.