The water permeability of blended polyethylene films

Abstract

Water vapour transmission (WVT) characteristics of blended polyethylene films blown from a 45 mm single-screw extruder were examined. For a given die gap size and blow-up ratio, it was found that WVT basically had an exponential decaying relationship with increasing film thickness. For a given film thickness, molecular orientation on the film in the machine direction could be increased by increasing the size of the die gap. It was found that WVT of blended polyethylene films which involved some proportion of long chain side molecular branches components were more susceptible to die gap size effect than those films only involving linear type molecules. This was thought to be attributed to the more molecular orientation in the machine direction. The results showed that for a given degree of orientation in the transverse direction, WVT decreased if film thickness and die gap size increased. This study also demonstrated that lower WVT required longer saturation time and smaller amount of saturated water vapour obtained.