VOC Sorption in Stretched Cross-Linked Natural Rubber

Sorption of volatile organic compound (VOC) vapors in natural rubber (NR) was measured at 20 degrees C using a magnetic suspension balance. Experiments were performed with non-cross-linked NR, as well as NR cross-linked with dicumyl peroxide. Stretching the cross-linked NR samples leads to crystal formation and therefore to a constraint to volume swelling of the amorphous domains. To investigate the influence of NR stretching and therefore of crystal formation on the VOC sorption, measurements of nonstretched NR were compared to data for cross-linked NR samples stretched with different extension ratios. Analysis of the VOC sorption data revealed a reduced VOC sorption in the stretched NR compared to fully amorphous, nonstretched NR. The sorption data were modeled using the perturbed-chain statistical associating fluid theory (PC-SAFT) accounting for network elasticity by an additional Helmholtz-energy contribution. Influence of crystallinity content on VOC solubility in stretched NR was finally accounted for following a recently proposed approach and thus accounting for an additional contribution to pressure in the amorphous phase as a result of constraint imposed by crystalline domains. Comparison of modeling results with measured solubility for several VOCs in NR confirmed the overall consistency of the modeling approach used.