Mechanism of Permeability Modification in Polyethylene Foams

Abstract

The shrinkage of low-density polyethylene (LDPE) foam obtained by the extrusion foaming method using isobutene as a blowing agent is suppressed and the dimensional stability is improved by blending with a permeation modifier of stearyl stearamide. To understand the mechanism involved in the modification of the permeability, the gas permeability and the surface structure of LDPE—stearyl stearamide blend films aged for various periods is investigated by using a gas transmission rate tester, scanning electron microscopy (SEM), attenuated total reflectance-infrared spectroscopy (ATR-IR), and grazing incidence X-ray diffraction (GIXD). After aging, a thin layer consisting of distorted particles appears at the surface of the blend film. The amount of stearyl stearamide at the surface increases as the aging time increases. These results suggest that the stearyl stearamide bleeds out to the surface of the film during aging. Gas permeability is suppressed by increasing the amount of stearyl stearamide that bleed out at the surface due to a decrease in solubility, and the permeability of isobutane becomes less than that of air over time. Such modification of permeability improves the dimensional stability of the LDPE foam in the extrusion and post-extrusion aging processes.