An Experimental and Theoretical Investigation into the Diffusion of Olefins in Semi-Crystalline Polymers: The Influence of Swelling in Polymer-Penetrant Systems (original) (raw)
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Polymer, 1996
Based on desorption and permeation measurements, the diffusivity and solubility of n-hexane and oxygen have been obtained for a wide range of linear and branched polyethylenes (PEs) with crystallinities between o 3 6 l 40 and 97 Vo and mass-average molar masses between 10 and 10 g mol-. The morphology and contents of crystal core (CC), crystal-core-like lnterfaclal (Icc), liquid-like interfacial (Ih) and liquid (L) components • " 13 n were assessed by transmission electron microscopy, Raman spectroscopy, C cross-polarizatio / magic-angle spinning nuclear magnetic resonance spectroscopy, differential scanning calorimetry, density measurements and small-angle light scattering. The penetrant solubility in the non-crystalline phases increased with increasing concentration of chain ends and chain branches. This effect was masked at certain crystallinities by the constraining effect of the crystallites. The diffusivity selectivity of oxygen over n-hexane increased strongly with increasing crystallinity and decreasing non-crystalline layer thickness, demonstrating that the crystal-induced constraint on the non-crystalline chains more efficiently retards the diffusion of larger molecules. The fractional free volume of the non-crystalline components decreased strongly with increasing crystallinity in the low-crystallinity range (<60%), above which it remained practically constant. The latter is because the constraining effect of the crystals is compensated for by the plasticizing effect of the chain ends, which leads to a constant free volume in this crystallinity range. A model, based on the Cohen-Turnbull-Fujita (CTF) model, considering the polymers to consist of four components, CC, Icc, Ir and L, was applied to the diffusivity data. The branched PEs and the majority of the linear PEs could be described by the modified CTF model. However, the lowest-molar-mass linear PEs exhibited a considerably larger interfacial free volume than the other samples. Real-time Raman spectroscopy on CC14-swollen samples showed that the changes in the CC and Icc contents during sorption were only small.
On the diffusion of gases in partially crystalline polymers
Journal of Polymer Science Part B: Polymer Physics, 1989
The diffusion of gases through partially crystalline polymers is studied. The effective diffusion coefficient DeB is obtained as the result of the averaged superposition of two fundamental mechanisms, namely, diffusion through the crystallites is considered to be zero, and diffusion through the rubbery fraction of the polymer obeys a Fujita-like free-volume theory. The predicted Deff is compared with experimental data of Kreituss and Frisch. The behavior of the diffusion coefficient in terms of concentration and crystalline fraction is satisfactorily explained through the model.
Macromolecular Symposia, 2010
Summary: Diffusion of n‐hexane in poly(ethylene‐co‐1‐hexene)s with 15–75 wt.% crystallinity was studied by desorption experiments analyzing data using the Fickian equations with a concentration dependent diffusivity. The effect of the impenetrable crystalline phase on the penetrant diffusivity (D) is described by D = Da/(τβ), where Da is the diffusivity of the amorphous polymer, τ is the geometrical impedance factor and β is a factor describing the constraining effect of the crystals on the non‐crystalline phase. For a polymer with 75 wt.% crystallinity, τβ varied markedly with penetrant concentration (v1a) in the penetrable phase: 1000 (v1a = 0) and 10 (v1a = 0.15). This penetrant‐uptake had no effect on the gross crystal morphology, i.e. β must be strongly dependent on v1a. Samples saturated in n‐hexane exhibited a penetrant‐induced loosening of the interfacial structure, as revealed by an increase in crystal density that require an increased mobility in the interfacial component ...
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Progress in Polymer Science, 1996
This paper is a review of the kinetics of diffusion of small-molecule penetrants in semi-crystalline polymers. The variations in diffusion impedance resulting from variations in morphology and segmental mobility in the amorphous component are highlighted. Deviations from Fickian diffusion appearing in many systems are discussed, as well as the effect of morphology, crystal orientation and chain orientation on the diffusivity.
Diffusion in polymeric systems–A review on free volume theory
Progress in Organic Coatings, 2017
This review paper deals the history and development of various theories to predict the diffusion in polymeric systems. The basis and application of various theories with the prediction capabilities are discussed. The most commonly used theory is Vrentas and Duda free volume theory with excellent agreement with experimental data report so far. This theory predicts the data very accurately in rubbery region. However, few modifications have come up in this theory to predict the diffusion above the glass transition with a little success. Relation between Fujita −Kishimoto theory [15] and Vrentas and Duda Theory [11,12] is
Chemical Engineering Science, 2008
Diffusion coefficient of propylene through polypropylene and ethylene through polyethylene, both in toluene and n-hexane, were estimated taking into account structural parameters of polymer chain and diffusing compound. In order to evaluate the influence of the structural variables considered in the prediction of the diffusivity and the swelling effects of the solvents, dynamic simulations of the metallocene-based slurry polymerization of propylene were performed using the assumptions of the multigrain model. The solvent influence was found to be more pronounced on the MAO diffusion, which is a larger molecule than the monomers propylene and ethylene. For n-hexane, the screening effects of the polymer chains were shown to hinder the diffusion of large molecules. The monomer concentration along the macro-and microscale particles was found to be quite constant, what can be attributed to the slight influence of the monomer diffusive transport in slurry polymerization of olefins, which is in agreement with the literature.
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Polymer, 2001
The diffusion coefficient for small molecules (solvent or monomer) through polymer solutions in the vicinity of the glass transition are known to change by as much as six orders of magnitude with only a small change in polymer concentration. Experimental measurements are difficult in this region and consequently there are data for only a limited number of systems. A rather simple method to estimate these diffusion coefficients for the rubbery, glass transition, and glassy regions as a function of polymer concentration and application temperature is presented. While the method is empirical in nature, it is based on carefully executed experimental studies, sound scaling laws, and agrees extremely well with free volume theories in the rubbery region. The method only requires a knowledge of the pure polymer glass transition temperature in order to estimate the diffusivity of molecules like styrenic and acrylic monomers (molecular weight of approximately 100 g/mol) at any polymer concentration and for temperatures above and below the polymer glass point. ᭧
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1991
DWusion cotlIlclents. denstties, and viscosltks have been measured ior dilute aoluttons of poIy(vinylldcn fluoride) In N.N-dlmethylformamlde and N-methylpixrolydone. and for two commercial samples of poly(suUone) in dlmethylacetatide. The results have been brIefly discussed with the nld of Flory-HuggIns and Stokes-Elnstdn equutlons.