Effects of uniaxial drawing and heat-treatment on gas sorption and transport in PVC

Sorption and transport measurements for various gases in rigid poly(vinyl chloride) were made following uniaxial drawing and heat treatment. The permeabilities of He, Ar, N₂, and CH₄ were found to be essentially independent of pressure in PVC while CO₂ showed a complex pressure dependence which varied with prior exposure and degassing history. Sorption isotherms were analyzed by the dual mode sorption model, and the parameters obtained were correlated with the Lennard–Jones potential-well depth of the gas. The Henry's law coefficient for CO₂ was found to be significantly larger than expected which is believed to be the result of a specific interaction with PVC. Uniaxial drawing of PVC above its glass transition caused significant reductions in gas permeabilities, of which roughly one-third is attributable to the accompanying heat treatment rather than molecular orientation per se. The physical state of the polymer was characterized by density, birefringence, and calorimetry. Changes in gas sorption and permeation behavior are discussed in terms of these results.