Gas Permeation in Semicrystalline Polyethylene as Studied by Molecular Simulation and Elastic Model (original) (raw)
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Behaviour of thermoplastic polymers during explosive decompressions in a petroleum environment
Le Journal de Physique IV, 1993
Thennoplastic polymers are used in the field of petroleum where they may encounter very severe conditions. So we are induced to study the ageing behaviour and the effect of rapid decompressions in a gaseous environment. In the latter case our aim is to define the limits of use and to identify the parameters influencing degradations. Such damaging is essentially of two types : (1) local in the form of blisters and (2) under extreme conditions, more homogeneous microscopic damage of the "foaming" type. Damage of the blistering type may threaten the integrity of the polymer part, and the microscopic damage does not necessarily affect the mechanical behaviour, for example the impact strength.
Modeling high-pressure gas–polymer mixtures using the sanchez-lacombe equation of state
Journal of Applied Polymer Science, 1988
The Sanchez-Lacombe equation of state was used to model the sorption of high-pressure gases into solid, amorphous polymers and molten polymers. Only one adjustable parameter per binary pair, a,,, was used in the mixing rules to correct the deviation of the characteristic pressure of the mixture, PG, from the geometric mean. The values of S,, which gave the best fit of the available literature data for the carbon dioxide-polymethyl methacrylate, carbon dioxide-silicone rubber, ethylene-low density polyethylene, methane-polyisobutylene, methane-low-density and highdensity polyethylene, and methane-polystyrene systems ranged from-0.019 to 0.136. In all cases, the calculated sorption isotherms were in reasonably good agreement with the experimental data. The resultant swelling of polymethyl methacrylate and silicone rubber was also well represented by the Sanchez-Lacombe equation of state. Because the Sanchez-Lacombe theory is based on latticefluid theory, the sorption calculations are limited to polymers which are noncrystalline, not cross-linked or slightly crosslinked, above their glass transition temperature, or above their melting temperature. The sorption data for the amorphous polymers considered in this study were either at temperatures above the glass transition temperature of the polymer or were at sufficiently high pressures that the temperature was above the effective glass transition temperature as predicted from a theoretical relation presented by Chow.
A mathematical model for predicting the permeability of natural gas in polymer nanocomposites was developed and tested using experimental data. The model takes into account the effects of pressure, temperature, crystallinity and nanoparticle loading. Three model parameters ( o D E , b and k ) were obtained. The parameter o D E is a measure of the activation energy, b described the effect of nanocomposite loading, and k can be used to describe the effect of gas concentration on the D E . Polymer nanocomposites were prepared using high density polyethylene as polymer matrix and Cloisite 15A as nanoclay. The proposed model was used to predict the permeability of the nanocomposites to pure CH 4 and mixed CH 4 /CO 2 gases (containing 80 mol% CH 4 ) at pressures up to about 106 bar and temperatures between 30 to 70 o C. Predicted results show that the developed model provides an excellent description of natural gas permeation in pure HDPE and its nanocomposites.
Journal of Polymer Science Part B: Polymer Physics, 2010
This article describes the diffusion and permeability of oxygen, carbon dioxide, methane, ethane, ethylene, propane, and propylene in 1-octene based polyethylene of densities 0.94, 0.92, 0.904, and 0.87. The isotherms obtained in the time-lag experimental device display a diffusion coefficient and permeability behavior similar to that of glassy polymers. We apply the dual model to semicrystalline polymers assuming that Henry's sites are related to the amorphous phase, which decreases when the crystallinity percentage increases. Whereas the interphase of the polymeric matrix and the crystalline phase prevails and acts as Langmuir sites. Their effect is to increase both, the tortuosity of diffusion trajectories and the chain immobilization. We now explain this effect using thermodynamic considerations. In fact, the tortuosity is related to the change in activation
The Journal of Chemical Physics, 2009
Isothermal compression of poly ͑dimethylsiloxane͒, 1,4-poly͑butadiene͒, and a model Estane ® ͑in both pure form and a nitroplasticized composition similar to PBX-9501 binder͒ at pressures up to 100 kbars has been studied using atomistic molecular dynamics ͑MD͒ simulations. Comparison of predicted compression, bulk modulus, and U s − u p behavior with experimental static and dynamic compression data available in the literature reveals good agreement between experiment and simulation, indicating that MD simulations utilizing simple quantum-chemistry-based potentials can be used to accurately predict the behavior of polymers at relatively high pressure. Despite their very different zero-pressure bulk moduli, the compression, modulus, and U s − u p behavior ͑including low-pressure curvature͒ for the three polymers could be reasonably described by the Tait equation of state ͑EOS͒ utilizing the universal C parameter. The Tait EOS was found to provide an excellent description of simulation PVT data when the C parameter was optimized for each polymer. The Tait EOS parameters, namely, the zero-pressure bulk modulus and the C parameter, were found to correlate well with free volume for these polymers as measured in simulations by a simple probe insertion algorithm. Of the polymers studied, PDMS was found to have the most free volume at low pressure, consistent with its lower ambient pressure bulk modulus and greater increase in modulus with increasing pressure ͑i.e., crush-up behavior͒.
High density polyethylene (HDPE)/clay nanocomposites containing nanoclay concentrations of 1, 2.5, and 5 wt% were prepared by a melt blending process. The effects of various types of nanoclays and their concentrations on permeability, solubility, and diffusivity of natural gas in the nanocomposites were investigated. The results were compared with HDPE typically used in the production of liners for the petroleum industry. Four different nanoclays-Cloisite 10A, 15A, 30B and Nanomer 1.44P-were studied in the presence of CH 4 and a CO 2 /CH 4 mixture in the temperature range 30-70°C and pressure range 50-100 bar. The permeability and diffusivity of the gases were considerably reduced by the incorporation of nanoclay into the polymer matrix. Addition of 5 wt% loading of Nanomer 1.44P reduced the permeability by 46% and the diffusion coefficient by 43%. Increasing the pressure from 50 to 100 bar at constant temperature had little influence on the permeability, whereas increasing the temperature from 30 to 70°C significantly increased the permeability of the gas. Additionally, the effect of crystallinity on permeability, solubility, and diffusivity was investigated. Thus, the permeability of the CO 2 /CH 4 mixture in Nanomer 1.44P nanocomposite was reduced by 47% and diffusion coefficient by 35% at 5 wt% loading, 50°C, and 100 bar, compared with pure HDPE.
Oil & Gas Science and Technology-revue De L Institut Francais Du Petrole, 2003
-Modélisation du comportement thermodiffuso-élastique linéaire couplé. Application à la décompression explosive de polymères-Une modélisation thermodiffuso-mécanique est proposée ici dans le but de décrire le comportement couplé de polymères initialement placés dans un environnement gazeux et sujets à une décompression « explosive ». Plusieurs descriptions du volume élémentaire représentatif (VER) pouvant répondre à cet objectif sont détaillées. La modélisation est ensuite conduite sur la représentation la plus simple du VER comme un mélange homogène de polymère et de gaz. Dans le cadre de la thermodynamique des milieux standard généralisés, les lois constitutives couplées sont établies en se limitant à un comportement mécanique élastique linéaire. L'implantation de ce modèle dans le logiciel ABAQUS™ a alors permis de mener une première étude qualitative des effets de couplages directs dont les principaux résultats sont discutés.
Journal of Membrane Science, 1998
Three types of novel correlations for activation energies of gas permeation E P and diffusion E D in amorphous glassy polymers are considered and their application for prediction of the E P and E D values for different gases are examined. The ®rst one is based on application of the group contribution method. Combined consideration of the equation of free volume and Arrhenius equation results in the correlation of E P and E D with free volume V f and fractional free volume (FFV). At last, the correlations between E P and the permeability coef®cient at a certain reference temperature P(T ref ), as well as E D versus D(T ref ), are based on the ful®lment of the so-called compensation effect between activation energies and preexponential factors in activated processes. Examples of applicability of the correlations considered and recommendations for their use in prediction of the E P and E D values are given for transport of various gases in glassy polymers and separately in amorphous glassy polyimides. #