Experimental Study on the Transport of Light Gas Molecules through Low-Density Polyethylene Films

摘要

An original experimental procedure for the study of gas permeation process through thin polymer films is presented. Employing mass spectroscopy techniques, this procedure allows the detection of the permeation flux with a signal-to-noise ratio large enough to obtain accurate measurements of the gas diffusivity also in processes with transient transport conditions lasting for short-interval times (similar to few seconds). The procedure is validated using as test material a thin low-density polyethylene (LDPE) film: the transport of four test gases with different molecular sizes and condensation properties (CO2, N-2, D-2, and He) is studied in the 295 to 350K temperature interval. The CO2 diffusivity values well compare with values previously obtained studying the same LDPE film samples by integral permeation technique measuring the time lag value. Original data on the diffusivity of the He and D-2 penetrant molecules are reported: in the examined temperature range, the diffusivity values of these small-size penetrants are in the 10-6 cm(2)/s range and follow an Arrhenius behavior with temperature. The activation energy values for diffusion are 18.8 +/- 0.4 and 10.0 +/- 0.4 kJ/ mol for D-2 and He, respectively.