M. Hedenqvist et al., POLYETHYLENE EXPOSED TO LIQUID PROPANE - SORPTION AND PERMEATION KINETICS AND MECHANICAL-PROPERTIES, Polymer engineering and science, 36(2), 1996, pp. 271-282
Data obtained by sorption and permeation measurements of liquid propan
e in medium-density polyethylene were analyzed with an analytical diff
usion model, assuming a constant diffusion coefficient, and a numerica
l model, based on the free volume theory of Fujita. The stress-strain
properties of propane-swollen medium-density polyethylene were recorde
d in an Instron tensile tester. The sigmoid sorption curves (modeled h
ere for the first time) were adequately described using nonstationary
boundary conditions. The numerical model was capable of representing s
orption, desorption, and permeation data, whereas the analytical techn
ique gave satisfactory results only for sorption/desorption data in th
e initial, transient stage. The difference between diffusion coefficie
nts determined from sorption and desorption measurements and the time
dependence of the modulus-solute concentration relationship can be exp
lained by assuming a relaxation of constrained amorphous chain segment
s. The penetrant-induced structure rearrangement is, according to diff
erential scanning calorimetry measurements, confined to the amorphous
phase.