The effect of biaxial deformation on the Nylon MXD6 on gas permeation properties was investigated. This polymer is known for its low oxygen permeability properties and it is typically used as tie layers in multilayer films and bottles in combination with other polymers. In this study the films of Nylon MXD6 were prepared by melt casting and then the stretched using different stretching modes (uniaxial constant width, simultaneous equal biaxial, and sequential biaxial), temperatures (105°C and 110°C), rates (0.00125s-1, 0.042s-1, 0.083s-1, and 0.125s-1) and to different stretch ratios. The stretched films were studied by online mechano-optical and off-line structural characterization techniques in order to observe the effect of orientation, crystallization, and oxygen permeability.
Through online mechano-optical studies during stretching, it has been found that the nylon MXD6 melt casted films studied exhibit a little increase in orientation (characterized by birefringence measurements) and a little increase in percent crystallinity.
The oxygen permeability of the films was measured and contrary to other publications found to increase (worsens) with biaxially stretching. This was correlated to the glass transition temperature. The glass transition temperature decreases with increased stretching which means there is more free volume in the further stretched samples. A combination of an increase in free volume and lack of crystallinity leads to an increase in oxygen throughput rate regardless of biaxial stretching mode.