Biaxially oriented poly(propylene-g-maleic anhydride)/phosphate glass composite films for high gas barrier applications

The solid state structure and oxygen transport properties of biaxially oriented poly(propylene-graft-maleic anhydride) (PPgMA) reinforced with a low glass transition temperature (Tg) phosphate glass (Pglass) were investigated. Composites were prepared by melt blending PPgMA with up to 20 volume% Pglass. Melt blended composites were compression molded into monolayer structures and then biaxially stretched at a temperature above the Tg of the Pglass. Scanning electron microscopy confirmed that biaxial stretching transformed the spherical Pglass particles into platelets oriented in the plane of the film. Gas transport measurements revealed a reduction in the oxygen permeability by as much as 2 orders of magnitude compared to the unoriented PPgMA film. The permeability was analyzed according to performance models for dispersions of platelet-like fillers proposed by Cussler and Nielson. Aspect ratios ranging from 15 to 80 were obtained by fitting the experimental data to the models. Mechanical tests revealed that blending with Pglass increased the modulus of the stretched film but reduced the elongation at break only slightly.