Solubility and diffusion of water in low-density polyethylene

Abstract

Solubility (S) and diffusion (D) of water in low-density polyethylene have been studied by means of desorption experiments. The dependence of S and D on the state of oxidation of the polymers has been measured. A model has been developed to describe the bound-oxygen dependence of S and D. Physically the oxygen groups act as traps that are strong enough to bind the water but not so deep as to remove the water from the diffusion process. Hydroxyl, hydroperoxide, and carboxylic acid groups form the strongest traps, ketone groups are weaker, and ester groups exhibit negligible trapping. Permeation is unaffected by bound oxygen. Trap volumes deduced from the analysis lie in the range of a few cubic angstroms. Some restriction of rotational motion of the trapped water is required by the analysis, and independent NMR evidence is presented to support this result.

Molecular modelling of oxygen and water permeation in polyethylene

“…These experiments have been conducted from 277 to 335 K, and the diffusion coefficients are ~10 -8 -10 -6 cm 2 s -1 . Similar results were obtained for water, where McCall et al [6] obtained an increase in diffusion coefficient from 6 × 10 -7 to 2 × 10 -6 cm 2 s -1 between 306 and 333 K.…”

“…[12] 0.75 [8] 0.69 [9] 0.740 0.706 0.684 0.686 [6] 0.500 b [13] 1 c [62] 0.479 b [63] 0.514 b 0.493 b a The numbers given are for calculation of D and P, but χ am = 1 was used for calculation of S, since crystallinity was already accounted for in the reference. b Not given explicitly in reference, but calculated from density.…”

“…Experimental measurements of water solubility in PE or systems similar to PE are in better agreement. Schatzberg [13] obtained an increase in solubility of water in n-hexadecane when increasing the temperature from 298 to 315 K, and McCall et al [6] obtained a similar increase for water in PE over a larger temperature range of 298 to 335 K.…”

“…It is evident from Figure 3 that including these atomic charges has a marginal effect on the PE density. Other studies are shown in grey and refers to: another simulation study ( ) [14], and experimental studies ( ) [4,5], ( ) [60], ( ) [61], ( ) [12] , ( ) [8], ( ) [9], ( ) [6], ( ) [13] and ( ) [62]. The experimental data are converted using equation 10 and the factors in Table 1 Solubility Figure 4 shows simulated and experimental solubility coefficients for oxygen and water in PE at 1 atm and temperatures from 278 K to 308 K. showing that the inclusion of atomic charges in the force field does not significantly affect the solubility coefficients.…”

“…Experimental studies provide valuable understanding of the macroscopic [4][5][6][7][8][9] and microscopic [10,11] properties of polymers and their transport properties. Michaels and co-workers [4,5] found that there is a slight increase in the solubility of oxygen in polyethylene between 285 and 315 K, and that a further increase in temperature results in a far larger solubility.…”