Permeation of gases through modified polymer films. V. Permeation and diffusion of helium, nitrogen, methane, ethane, and propane through γ‐ray crosslinked polyethylene

Abstract

SynopsisThe permeation and diffusion of helium, nitrogen, methane, ethane, and propane through y-irradiated polyethylene films were investigated. These studies were carried out with two objectives in mind: (1) to determine the effect of crosslinking by y irradiation on permeability and diffusivity using the gas molecules as molecular probes; and (2) to study the plasticizing effects of the low hydrocarbons on the polyethylene film. The y-ray-induced crosslinking efficiency of polyethylene was investigated in the following irradiation atmospheres: vacuum, acetylene, and nitrogen-acetylene mixtures. Results showed that irradiation in acetylene decreased the crosslinking efficiency while an acetylene-nitrogen atmosphere increased the efficiency compared to irradiation in vacuum. Both the permeation constants and the diffusion coefficients were found to decrease with increasing irradiation dose while the activation energies increased. The permeation constants of the organic gases through polyethylene increased with molecular diameter while the diffusion coefficients decreased. This increase in permeability was attributed to an increase in the solubility due to solubilization of the membrane by the penetrant. For example, the molecular diameter of propane is 4.397 A compared with 2.807 8, for methane; however, propane permeated the polyethylene film a t a rate twice that of methane. Nitrogen and methane have approximately the same molecular diameters-2.7085 and 2.807 A, respectively-but owing to the plasticizing effect of methane, it permeated the film at a rate three times greater than that of nitrogen. I t is interesting to note that the stronger the plasticizing ability of the penetrant, the greater the effect of the irradiation dose. The permeability of propane decreased by 40.7%, while the permeability of helium decreased by 6.4% after an irradiation dose of 50 Mrad.

Heat Curing of Whey Protein Films

“…A reduction in gas transmission in irradiated polyethylene was attributed to increased cross-linking (Bixler et al, 1963;MacDonald and Huang, 1981). A reduction in the sorption of several flavor compounds in polyethylene and ethylene vinyl acetate polymers was also found (Matsui et al, 1990(Matsui et al, , 1991(Matsui et al, , 1992.…”

“…In addition to the application or generation of heat, curing may involve a reaction catalyst (Chan and Feke, 1993) or irradiation (MacDonald and Huang, 1981) to induce desired cross-linking. The increased structural cohesion resulting from cross-linking often results in more effective barrier properties against gas, vapors, and solutes (Kester and Fennema, 1986).…”

“…Curing is commonly used to cross-link synthetic thermoset polymers, though some researchers have examined heat curing of thermoplastic polymers (El-Hibri and Paul, 1985;Perkins, 1988). In addition to the application or generation of heat, curing may involve a reaction catalyst (Chan and Feke, 1993) or irradiation (MacDonald and Huang, 1981) to induce desired cross-linking. The increased structural cohesion resulting from cross-linking often results in more effective barrier properties against gas, vapors, and solutes (Kester and Fennema, 1986).…”

Numerical Analysis of a Continuous Vulcanization Line to Enhance CH4 Reduction in XLPE-Insulated Cables

“…At the ambient temperature, XLPE has a semicrystalline structure, but the crystallites begin to melt at approximately 70 °C [ 1 ]. Because the semicrystalline structure may considerably affect the diffusion within XLPE [ 38 , 39 , 40 ], the effect of phase changes on the diffusion coefficient must be considered to ensure accurate byproduct transport analysis. As shown in Figure 7 , thus, we use the experimentally measured diffusion coefficient profile for semicrystalline XLPE at low temperatures [ 22 ] and that for the amorphous phase estimated via molecular dynamic simulations [ 41 ] at high temperatures.…”

Numerical Study of CH4 Generation and Transport in XLPE-Insulated Cables in Continuous Vulcanization

“…Normally, the XLPE has a semi-crystalline structure, but the crystalline structure starts to melt at around 70°C [1]. Since the crystalline structure may significantly affect the overall diffusion property in the XLPE [30][31][32], knowing the effect of phase changes on the diffusion coefficient is important for the accurate analysis of byproduct generation and transport. In this study, hence, we combined two available diffusion coefficient profiles that represent the experimentally measured semi-crystalline structures [17] and the amorphous phases, as estimated by molecular dynamic simulations [33][34][35] to cover the different temperature ranges.…”