The effect of relative humidity on the permeability of toluene vapour through a multi‐layer coextruded film containing hydrophilic layers

The effect of relative humidity on the diffusion of toluene vapour through a multi‐layer coextrusion film structure containing moisture sensitive hydrophilic barrier layers (nylon and EVAL) was evaluated. Two experimental test methods were employed. In Method I, the effect of relative humidity on the diffusion of toluene vapour was evaluated, where the test film was preconditioned to a fixed water activity prior to test. In Method II, the effect of water vapour as a co‐permeant was evaluated. Studies carried out by Method I showed the concentration dependency of the diffusion process and the importance of relative humidity on the diffusion of organic vapour through barrier structures. Water vapour was found to exhibit strong interactive effects with the moisture sensitive polymer layers of the laminate, which resulted in an increase in the diffusion of toluene vapour through the barrier structure. When the effect of water vapour as a co‐permeant was evaluated (Method II), the direction of permeation (i.e. surface exposed to high relative humidity and vapour concentration) markedly influenced the resultant barrier properties.