Effect of postdrawing on the permeability of gases in blown polyethylene film

Abstract

AbstractThe effect of orientation on the structure and transport properties of high‐density polyethylene film has been studied. Microstructure was characterized using small‐angle light scattering, birefringence, and wide‐angle x‐ray scattering. Water vapor and oxygen transmission rates were determined as a function of film draw ratio. The object of the present work is to correlate the effects of postprocessing conditions on the transport properties and morphology of linear polyethylene. High‐density spherulitic polyethylene films were produced by blown film extrusion and subsequently oriented by longitudinal stretching in a postoperation. Various degrees of orientation were imparted to the films, with percent crystallinity, sample orientation and transport properties measured as a function of draw ratio. For the postoriented films, results indicate there was no significant change in percent crystallinity with increasing draw ratio although water vapor and oxygen permeability decreased substantially. This is attributed to the increased orientation of the crystalline and amorphous regions and rod‐like and microfibril structure formation brought about by the drawing process. Lower processing temperatures result in increased orientation which improves the vapor barrier properties.