Effect of lamellar microstructure on the permeability of polyethylene films

Lamellar microstructures can decrease the permeability to gases and vapors by increasing the diffusive path in plastic films, or the so-called tortuosity which depends on the aspect ratio, orientation, and the volume fraction of the dispersed material. In this research, different types and percentages of mica with relatively high aspect ratio are used as oxygen barrier materials in blown films. Both high and low density polyethylenes (HDPE and LDPE), as well as their blends are used as the matrix materials. A decrease in permeability of both LDPE and HDPE films to oxygen is achieved with increasing volume fraction of the higher aspect ratio mica. By contrast, use of the coarser mica grades did not result in the anticipated properties in HDPE films. In all cases, the morphology of the films corresponded to several overlapping, discontinuous mica layers with the broad faces of mica, essentially parallel to the surface of the films. Rheological properties, morphology, and mechanical properties were also examined. The experimentally determined permeability and elastic modulus values were found to be in good agreement with theoretical predictions. By contrast to LDPE, the processability of HDPE films was found to decrease dramatically with increasing mica loadings, It was found that optimization of barrier properties in HDPE films through addition of mica flakes is a compromise between the desired reduction in permeability and the loss in processahility and ductility