Solubility of solvents in polyethylene below the melt temperature

Polyethylene, the most ubiquitous polymer in use, is a semi-crystalline material. Solvents enter only the amorphous phase. The solubility in that phase, however, cannot be characterized by the amorphous solubility found above the melt temperature. The polymer chains that have ends attached to the crystalline structure but extend into the amorphous phase are referred to as tie chains, and they affect the overall solvent solubility. Six different polyethylenes covering a range of densities were studied. Below the melt temperature all the samples exhibited an increase in solubility with increasing temperature. The solubility of the penetrants, however, is not the same for different types of polyethylene. A model which incorporates an elasticity factor that accounts for the stress effects on the solubility in the tie chains was found to be valuable. When incorporated into a version of the UNIFAC free-volume model there was good correlation between of the solubilities. The present work indicates that the tie chain fraction, f, tends to increase with density. (C) 2017 Elsevier B.V. All rights reserved.