ETHYLENE SOLUBILITY AND DIFFUSION IN LOW-DENSITY POLYETHYLENE AND ETHYLENE COPOLYMERS

Evolution rate measurements were conducted to determine the solubility and the diffusion constants of ethylene in three semicrystalline polymers: low‐density polyethylene (LDPE), ethylene‐ethyl acrylate (EEA), and ethylene–vinyl acetate (EVA) copolymers. The apparatus for such measurements utilizes a flame ionization detector interfaced to a computer for continuous monitoring of the ethylene evolution from the polymer pellets. Solubilities are obtained by calculating the total ethylene evolved over a 12–48‐hr period. Analysis of the evolution rate data in terms of the nonsteady‐state diffusion equation for spheres yields the diffusivity. The ethylene solubility and diffusion constants in EVA and EEA are very similar to those in LDPE. This is due to compensating effects of decreased crystallinity and increased cohesive energy density with the incorporation of bulky polar groups into the polymer chain. Copyright © 1979 John Wiley & Sons, Inc.