Anionic copolymers of octanelactam with laurolactam (nylon 8/12 copolymers). VII. Study of diffusion and permeation of gases in undrawn and uniaxially drawn (conditioned at different relative humidities) polyamide films

The permeability coefficient of a wide range (0/100–100/0 octanelactam/laurolactam [OL/LL] mol/mol) of novel copolyamides (nylon 8/nylon 12) was determined and related to the diffusion rate over a range of temperatures: Tg–30 to Tg + 40°C. An inflection in the plot of permeability vs. 1/T (K) provided an indirect indication of glass transition value and agreed satisfactory with DSC and DMTA measurements. Both uniaxially drawn and undrawn membranes were evaluated and the permeability values were correlated with the % crystallinity. The reduction in solubility, diffusivity, and permeability with increasing draw ratio was attributed to a substantial increase in % crystallinity. Finally, the effect of absorbed water on gas permeability of polyamide films was examined. In most homopolyamides and copolyamides, the higher the water absorption of films the higher the permeability values.