Processing/Structure Relationships of Mica-Filled PE-Films with Low Oxygen Permeability

Abstract

Abstract Lamellar microstructures can decrease gas and vapor permeability by increasing the diffusive path or the so-called “tortuosity” in plastic films. In this research, phlogopite mica flakes were used as oxygen barrier materials in films produced in a blown film extrusion line. Both high and low density polyethylenes as well as their blends were used as matrices with mica concentrations not exceeding 10-wt.-%. A decrease in oxygen permeability of both low density and high density polyethylene films was achieved with increasing volume fraction of mica. Film morphologies indicated strong flow-induced orientation of the flakes in overlapping, discontinuous layers that were reasonably well oriented parallel to the surface of the films. Melt shear viscosity and melt strength of the mica compounds and tensile properties of films were also examined and correlated with processability. Overall, it was found that, by contrast to the LDPE compounds, optimization of the barrier properties of the HDPE films was a compromise between the desired reduction in permeability and the loss in processability and film ductility. The experimentally determined elastic modulus values were found to be in relatively good agreement with predictions from flake reinforcement theories. A predictive model for the analysis of the permeability results, assuming that both mica flakes and the crystalline domains of the films were impermeable to oxygen, was able to describe the permeability results in spite of several simplifying assumptions.