PROCESSING STRUCTURE RELATIONSHIPS OF MICA-FILLED PE-FILMS WITH LOW-OXYGEN PERMEABILITY/

Lamellar microstructures can decrease gas and vapor permeability by in creasing the diffusive path or the so-called ''tortuosity'' in plastic films. In this research, phlogopite mica flakes were used as oxygen b arrier materials in films produced in a blown film extrusion line. Bot h high and low density polyethylenes as well as their blends were used as matrices with mica concentrations not exceeding 10-wt.-%. A decrea se in oxygen permeability of both low density and high density polyeth ylene 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 s trength of the mica compounds and tensile properties of films were als o examined and correlated with processability. Overall, it was found t hat, by contrast to the LDPE compounds, optimization of the the barrie r properties of the HDPE films was a compromise between the desired re duction in permeability and the loss in processability and film ductil ity The experimentally determined elastic modulus values were found to be in relatively good agreement with predictions from flake reinforce ment theories. A predictive model for the analysis of the permeability results, assuming that both mica flakes and the crystalline domains o f the films were impermeable to oxygen, was able to describe the perme ability results in spite of several simplifying assumptions.