Stress‐enhanced transport of toluene in poly aryl ether ether ketone (PEEK)

Abstract

SYNOPSISThe transport of fluids in the semicrystalline polymer, poly(ary1 ether ether ketone) (PEEK), was investigated. Both solubility and rate of penetration of toluene into PEEK are markedly increased by the application of an external stress. The induction period (i.e., the time for the sorption to begin) is a function of applied stress as well as temperature and crystallinity. At 22°C in 29% crystalline PEEK the induction period was reduced from more than 2000 h to approximately 10 h whereas the solubility of toluene was increased from 9 to 44 wt % upon the application of an external tensile stress of 30 MPa. A critical stress (i.e., a stress value below which the stress-enhanced effects are not observed) was determined. The critical stress is a strong function of crystallinity and temperature. 0 1996 John Wiley & Sons, Inc. Keywords: toluene fluid transport stress-enhanced effects poly(ary1 ether ether ketone)

Transport of small molecules through mechanically elongated polymeric membranes

“…The breakthrough time has been experimentally correlated to the thickness of the membrane for various polymer‐solvent systems, so the trend predicted by eq. (21) also agrees with experimental data as transport through thinner membranes exhibits shorter breakthrough times 11, 14…”

“…The increase in flux is in agreement with experimental data, as a larger γ 2 implies a larger effect of E , the elastic diffusion coefficient, on the transport of chemicals through polymeric membranes. This prediction may be useful in explaining previously reported cases of stress‐enhanced transport 10, 11, 14. An increase in γ 2 also increases the time to reach a maximum flux.…”

“…This prediction is also in agreement with experimental data as an increase in mechanical deformation of the polymeric membrane implies an alignment of the polymer chains and hence an increase in localized crystallinity. This morphological change, increasing the value of E , causes the transport of the solvent to be slower so the time to reach a maximum flux decreases 14–16…”

Non-Fickian diffusion in systems with complex interfaces

“…They attributed this difference to irreversible structural changes of the HDPE. 12 This study found that the solubility and rate of diffusion into the resin are greatly increased by the application of stress. The HDPE film is gradually transformed into a fibrillar structure, substantially reducing the number of sorption sites.…”

“…This is consistent with the results of Choy et al, 78 who found that high draw ratios induce structural changes in polyethylene. 12 Other studies have observed that external stress, either uniaxial tensile stress or fabrication residual stress, produced an enhanced equilibrium solubility and an accelerated rate of diffusion, 83,84 however, none of these studies performed the permeation or solubility experiments when the membranes were in a state of deformation. Drummond et al 79 used atomic force microscopy (AFM) to study the structural changes due to external deformation.…”