On the CO₂ permeation of uniaxially drawn polymers

The CO 2 permeation coefficient and the difficient were measured using the permeation time‐lag method for films of atactic polystyrene and high‐density polyethylene, each as a function of uniaxial draw ratio. The reduction of permeability with draw ratio is observed for polystyrene and for polyethylene. In the latter it is associated with an increase in crystallinity. In both cases the premeability decreases and the solubility constant remains unchanged. The reduction of permeability is thus caused only by the reduction in diffusion of CO 2 in the drawn polymers. The mechainism is different for the two polymers, as is confirmed by measurements of birefringence, glass transition temperature, and crystallinity.