Elastic effects on solubility in semicrystalline polymers

Abstract

Capillary column inverse gas chromatography experiments at infinite solvent dilution were conducted for 15 polyethylene/solvent systems. Thermodynamic data were collected for various types of penetrant molecules (normal alkanes, 1-alkenes, isomers of hexane, and ring compounds). Theoretical predictions of the solubility data were made with an activity coefficient model (Universal Functional Group Activity-van der Waals-Free-Volume) (UNIFAC-vdw-FV) and an equation-of-state model (GroupContribution, Lattice-Fluid, Equation of State) (GCLF-EoS). Although good agreement between the experimental data and theoretical predictions was obtained above the melting point of the polymer, at temperatures below the melting point, significant differences were found. This occurred because at those temperatures, the polymer had a semicrystalline structure and the solubility of the solvent was reduced on account of the constraints on some of the chains in the amorphous phase by the polymer crystallites. The theory developed by Michaels and Hausslein to account for such elastic effects on solubility was incorporated into the two predictive models. After these modifications, the new estimations of the solubility showed significantly improved agreement with the experimental results. Moreover, the elasticity effect resulted in elevated estimates of the crystallinity when inverse gas chromatography retention volumes were used.

Gas Permeation in Semicrystalline Polyethylene as Studied by Molecular Simulation and Elastic Model

“…The correction term is usually introduced as a contribution to the activity coefficients of the different species. Some modified equations of state are proposed that allow the calculation of thermodynamics properties including the elastic effect contribution [40,[44][45][46][47]67]. Different elastic models exist in the literature.…”

“…All quantities required in Equation (15), except f , have been taken from experimental results of Flaconnèche et al obtained on a medium density polyethylene sample [66]. Few authors have reported values for the empirical factor f in order to reproduce solubility data of penetrants in different PE samples [39,44,45,47]. f values are typically in the range 0.27-0.50.…”

“…The network formed by these tie segments may constrain the amorphous regions of the polymer. This effect, called the elastic effect, has been invoked by several authors to correct the predicted solubilities by equations of state or group contribution methods [44][45][46][47] but was never accounted for in molecular simulations.…”

Combined EoS and elastic constraints models to predict thermodynamic properties for systems involving semi-crystalline polyolefins

“…Over the past few decades, a number of studies had been performed to evaluate both experimentally and theoretically the solubility of a-olefins in semi-crystalline polyolefins over a wide range of pressures and temperatures [1,6,[8][9][10][11][12][13][14][15][16][17][18]. However, the open source information on multi-component solubilities of a-olefins, diluents and inerts in semi-crystalline polyolefins is scarce.…”

Kinetic modelling of phenols consumption during polyethylene thermal oxidation

“…This is not surprising first because approach derived from Flory's theory cannot be when polar interactions exist between polymer and stabilizer, and also because of the semi-crystalline nature of polyolefins [21]. Hence, the solubility of a stabilizer in a polyolefin can only be estimated from reported experimental values together with some structure properties relationships [22].…”