Kinetics and equilibria of sulfur dioxide sorption in kapton polyimide

The kinetics and equilibria of SO₂ sorption in Kapton polyimide film have been measured at 25°C for pressures up to 58 cm Hg using a quartz spring balance. The observed equilibria are described well by the dual-mode model for sorption of penetrants in glassy polymers. Observed hysteresis in sorption-desorption cycling indicates that the diffusivity of SO₂ increases markedly with increasing local penetrant concentration in the polymer. The concentration dependence of the effective average diffusion coefficient is described well by an expression from dual-mode theory. The Langmuir component of the sorption population has an extremely low mobility compared to that of the Henry's law component; in fact, the so-called “total immobilization” limiting case, which assigns a zero diffusion coefficient to this component, appears to be satisfactory under the conditions studied. These results, coupled with published results for other penetrants, suggest that the degree of immobilization of the Langmuir population depends to a great extent on the condensability and/or the molecular size of the penetrant. Predictions of the SO₂ diffusion time lag and permeability in Kapton as functions of the upstream SO₂ pressure are presented and discussed in terms of the dual-mode theory.     

The effect of morphology on sorption and transport of carbon dioxide in poly(4,4'-oxydiphenylene pyromellitimide)

Sorption and transport of carbon dioxide were investigated for poly(4,4'-oxydiphenylene-pyromellitimide) films (PI-1, PI-2, and PI-3) imidized at 160, 200, and 400°C, respectively, as well as for a chemically identical commercial polyimide film, Kapton-H. The solubility, permeability, and diffusion coefficients (S, P, and \[ \overline D \] , respectively) at 80°C and 20 atm in PI-3 were 67, 25, and 37%, respectively, as large as those in PI-2. These significant reductions are attributed to a higher degree of segmental aggregation in PI-3 caused by a 1.7% increase in the density (d) as compared with PI-2. The differences in S, P, \[ \overline D \] , and d between PI-3 and Kapton-H were rather small as compared with those between PI-3 and PI-2, suggesting that the in-plane orientation has a minor effect on the sorption and transport in Kapton-H as compared with the aggregation. Influence of the morphology on the dual-mode sorption and transport parameters was also investigated. With increasing density, the Langmuir capacity constant and the diffusion coefficients for the Henry's law and Langmuir populations decreased by higher rates than the Henry's law solubility constant, being contrary to the results reported for a typical semicrystalline glassy polymer, polyethylene terephthalate. This may suggest that the nonaggregated or less-aggregated regions taking an important part in the sorption and transport are denser for the sample having a higher overall density.     

Carbon dioxide sorption and transport in polycarbonate

The solubility, permeability, and diffusion time lag for carbon dioxide in polycarbonate are reported at 35°C for pressures ranging from 1 atm to 23 atm. The solubility data are very well described by the dual sorption mechanism model, Henry's law plus Langmuir adsorption, proposed for glassy polymers. Both the permeability and time lag decrease with increased CO₂ pressure. These observations are not consistent with the proposal that CO₂ sorbed by the Langmuir contribution is totally immobilized; however, all of the results are entirely consistent with an extension of this proposal which considers partial immobilization. The data have been quantitatively analyzed in terms of this partial immobilization model, and the results suggest for polycarbonate at 35°C that the CC₂ sorbed by the Langmuir portion of the isotherm behaves as if it has only about 10% of the mobility of the gas sorbed by the Henry's law part of the isotherm. The results have also been interpreted in terms of a concentration-dependent diffusion coefficient which is shown to be mathematically equivalent to the partial immobilization model. The latter model was also formulated in thermodynamic terms, whereby fugacity was used rather than pressure, and diffusion coefficients were defined in terms of chemical potential gradients rather than concentration, but the consequences of these changes proved to be minor and no better. The significance of these observations and their interpretation is discussed.     

Dual mode model for mixed gas permeation of CO2, H2, and N2 through a dry chitosan membrane

Dry chitosan is an excellent candidate for facilitated transport membranes that can be utilized in industrial applications, such as fuel cell operations and other purification processes. This article is the first to report temperature effects on transport properties of CO₂, H₂, and N₂ in a gas mixture typical of such applications. At a feed pressure of 1.5 atm, CO₂ permeabilities increased (0.381–26.1 barrers) at temperatures of 20–150 °C with decreasing CO₂/N₂ (19.7–4.55) and CO₂/H₂ (3.14–1.71) separation factors. The pressure effect on solubilities and permeabilities were fitted to the extended dual mode model and its corresponding mixed gas permeation model. The dual mode and transport parameters, the sorption heats and the activation energies of Henry's and Langmuir's regimes and their pre‐exponential parameters were determined. The Langmuir's capacity constants were utilized to estimate chitosan's glass transition temperature (CO₂: 172 °C, N₂: 175 °C, and H₂: 171 °C). The activation energies of diffusion in the Henry's law and Langmuir regimes were dependent on the collision diameter of the gases. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2620–2631, 2007     

Dilation of poly[1-(trimethylsilyl)-1-propyne] during sorption of n-nonane

The linear expansion and contraction in the principal planar directions of poly[1-(trimethylsilyl)-1-propyne] film were measured concurrently with the sorption of n-nonane at 35°C. After the first sorption cycle, in which the polymer exhibited markedly nonisotropic volumetric dilation, the polymer expanded and contracted reproducibly during subsequent multiple sorption and desorption cycles. These reversible dilation isotherms were reproducible from sample to sample. The fractional change in length was identical in arbitrarily selected, orthogonal directions in the plane of the film, suggesting that the expansion and dilation of the sample are isotropic. When plotted versus the activity of n-nonane, the linear expansions in the plane of the film are slightly concave to the activity axis, reaching levels over 10% at the highest activities. The experimental partial specific volume of the polymer is near its pure component value but that of the penetrant is much less than its pure component value. Moreover, the magnitude of dilation observed is described rather closely by the dilation which would result solely from the Henry's law portion of sorption, assuming zero volume-change of mixing. These results are consistent with the explicit notions of “hole-filling” associated with the Langmuir mode in the dual-mode model. © 1993 John Wiley & Sons, Inc.     

CO2 sorption in poly(ethylene terephthalate) above and below the glass transition

High-pressure CO₂ sorption data in semicrystalline poly(ethylene terephthalate) (PET) are presented for temperatures ranging from 25 to 115°C. The results are described by Henry's law above the glass-transition temperature of PET, while a dual-mode sorption model comprised of a Henry's law and a Langmuir isotherm applies in the glassy state. The disappearance of the Langmuir capacity of the polymer above T_g presumably results from the elimination of regions of localized lower density which are frozen into the glass upon quenching from the rubbery state. Exposure of PET to a high CO₂ pressure produced a systematic variation in the apparent sorption equilibria. Correlation of the Langmuir capacity of PET with the dilatometric parameters of the polymer provides a useful framework for understanding the origin of the Langmuir sorption mode and for interpreting annealing and conditioning effects in glassy polymers.     

CO2 sorption in uniaxially drawn atactic polystyrene

The CO₂ solubility in oriented and unoriented atactic polystyrene films has been investigated. Orientation does not change the nature of the sorption process; however, it decreases the level of solubility. Both the Langumir sorption term and the Henry's-law contribution are affected by orientation. The decrease of solubility is correlated with an increase of density due to orientation. A simple experiment has been described to evaluate the depression of the glass transition temperature of polystyrene containing dissolved carbon dioxide.     

Gas sorption and transport in a copolyester and its blend with polycarbonate

Sorption and transport measurements for various gases were made with a copolyester formed from 1,4-cyclohexanedimethanol and a mixture of terephthalic and isophthalic acids. Similar observations for the miscible blends of this copolyester with polycarbonate were made using carbon dioxide. All of these results are described well by dual sorption-dual mobility models which have been used effectively for other gas-glassy polymer systems. The sorption and transport parameters deduced experimentally from these systems have been correlated and interpreted in terms of applicable theories. For the blends, the Henry's-law sorption parameter has been used to deduce a reasonable value of the interaction parameter for the polycarbonate-copolyester blend system from the Flory-Huggins theory of mixtures. The Langmuir capacity term from the dual-sorption model is accurately related to the unrelaxed volume of the glass. Negative deviations of permeability and diffusion coefficients from simple additivity relations were observed and qualitatively interpreted to result from the decrease in volume on mixing for the blends.     

Gas sorption and transport in substituted polycarbonates

The effects of molecular structure manipulation of polycarbonates on sorption and transport of various gases were studied using tetramethyl, tetrachloro, and tetrabromo substitutions onto the aromatic rings of bisphenol A polycarbonate. Solubility and permeability measurements were made at 35°C over the pressure range of 1–20 atm for a variety of gases, namely CO₂, CH₄, O₂, N₂, and He. A threefold to fourfold increase in permeability was caused by the tetramethyl substitution, whereas the tetrachloro and tetrabromo substitutions reduced the permeability relative to the tetramethyl substitution. Lower activation energies for transport were found for the tetramethyl polycarbonate relative to the unsubstituted polycarbonate. Permeability coefficients were factored into solubility and diffusion coefficients. Sorption levels increased for all substitutions, but among the substituted polymers the levels remain practically the same. Solubility data were analyzed in terms of the dual sorption model. The Henry's law solubility coefficients obtained from this analysis were found to be consistent with a predictive equation developed for rubbery polymers. The usual correlation for predicting the Langmuir sorption capacity of the model overestimates the values for the substituted polycarbonates, and a proposal for the cause of this is offered. Thermal expansion of these polymers was measured using dilatometry, and the results are used in the interpretation of the sorption data. Diffusion phenomena are explained by segmental mobility and free volume considerations. The effects of CO₂ exposure history on sorption and transport were also investigated.     

Transient and steady-state water vapor permeation through polymer films

Water vapor transport properties for the polymers Kapton H

1 Reference to a company or product name does not imply approval or recommendation of the product by the University of California or the U.S. Atomic Energy Commission to the exclusion of others that may be suitable.

and Parylene C were determined over a temperature range of 20 to 55°C. Activation energies and entropies for permeation as well as partial molar free energies, heats, and entropies of dilution were calculated for water vapor concentrations ranging from 3 × 10^?6 to 1 × 10^?3 mole H₂O per cm³ of polymer. Mylar A was tested to extend the available data for partial molar heats and entropies of dilution and to compare permeation and diffusion results with the corresponding values in the literature. Diffusion coefficients were measured using the time-lag technique of Barrer but employing a modified test apparatus. Equilibrium sorption isotherms at 30°C were obtained for Mylar A and Kapton H with a Cahn microbalance. The ratios of the permeability to diffusion coefficients as measured from time-lag experiments agreed with solubility coefficients within 3% for Mylar A and within 12% for Kapton H. Both polymers obeyed Henry's law. The results were interpreted in light of polymer polarity and morphology.     

Sorption and partial molar volume of gases in poly (dimethyl siloxane)

Sorption of N₂, O₂, Ar, CH₄, CO₂, C₂H₄, and C₂H₆ in poly (dimethyl siloxane) liquid and rubber and the dilation of the polymers due to sorption of the gases are studied at 25°C under pressures up to 50 atm. In the liquid, the sorption isotherms for low-solubility and high-solubility gases are described by Henry's law and the Flory–Huggins equation, respectively. Gas sorption in the rubber, which contains a 29 wt % silica filler, follows the dual-mode sorption model, though marked hysteresis is observed in the sorption of O₂ and CH₄. The dilation isotherms increase linearly or exponentially in both polymers with increasing pressure. Considering that gas molecules adsorbed into micropores of the filler particles do not participate in the dilation, partial molar volumes of the dissolved gases in the rubber are determined from data of sorption and dilation. The values are nearly equal to the partial molar volumes in the liquid (48–60 cm³/mol).     

Moisture sorption in polyamide 6.6: Experimental investigation and comparison to four physical-based models

Water sorption in polyamide 6.6 has been characterized for a wide range of temperature (25°C to 80°C) and various water activities using a Dynamic Vapor Sorption testing machine. Complex sorption mechanisms govern the water uptake in the material. The competition between two main temperature dependant mechanisms has been observed: a Henry's sorption mechanism that mainly governs the sorption curve at low water activities, and a second mechanism at high water activities that could be related to the formation of water clusters. It is observed that the temperature dependency can mainly be attributed to the Henry's contribution. Four physically based models are then used and identified thanks to the extended experimental database. It is shown that a simple Flory-Huggins model is not able to capture the experimental observations at very high water activities for all the temperatures tested. The ENSIC model is a better choice, but good prediction for very high water activity cannot be obtained. Both modified Park and GAB models can accurately predict the volume fraction of water for the whole ranges of water activity and temperature, although the modified Park model should be preferred considering the number of parameters and the mathematical simplicity.     

Gas sorption and transport in polysulfone

The sorption and transport of CO₂, CH₄, Ar, and N₂ were measured in a melt-extruded film of polysulfone at 35°C. The results are interpreted in terms of the dual sorption and mobility models and compared to the structurally similar glassy polycarbonate. In addition, sorption measurements were made on specimens with various processing and treatment histories including porous membranes prepared by water coagulation of concentrated polysulfone solutions in DMF and THF. The sorption capacity for CO₂ varied considerably with the history of the specimen.     

Gas sorption in poly(vinyl benzoate)

High-pressure sorption (up to 50 atm) for CO₂, N₂, and Ar in poly(vinyl benzoate) (PVB) was studied at temperatures from 25 to 70°C by a gravimetric method utilizing an electromicrobalance. The results are described by Henry's law above the glass transition temperature T_g for all gases. The dual-mode sorption model, Henry's law plus a Langmuir isotherm, applies to the sorption isotherms of N₂ and Ar in the glassy state, and the dual-mode parameters are given. For CO₂, a new type of sorption isotherm is observed below T_g. The isotherm is concave to the pressure axis in the low-pressure region and turns into a straight line with increasing CO₂ pressure which can be extrapolated back to the coordinate origin. The linear part of the isotherm is characteristic of the rubbery state, while the nonlinear part stems from glassystate behavior. The “glass transition solubility” of CO₂, at which PVB film changes from the glassy to the rubbery state, decrease as the temperature increases. The disappearance of microvoids, that is, the decrease of the Langmuir capacity, may be due to a large plasticizing effect of sorbed CO₂. The difference between the N₂ and Ar isotherms and the CO₂ isotherm is discussed from this standpoint.     

The effect of morphology on sorption and transport of carbon dioxide in a polyimide from 3,3′,4,4′-biphenyltetracarboxylic dianhydride and 4,4′-oxydianiline

Sorption and transport of CO₂ have been investigated for polyimide films prepared from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 4,4′-oxydianilline (ODA) as well as for a chemically identical commercial polyimide film, Upilex-R. The BPDA-ODA polyimide films annealed above the glass transition temperature (270°C) are found to have some degree of ordering owing to molecular aggregation of polymer chains, whereas the films as-cast are amorphous. The solubility, permeability, and diffusion coefficients decrease significantly with increasing density or increasing average degree of molecular aggregation. The influence of morphology on the parameters in the dual-mode sorption and transport model has also been investigated. With an increase in density, the Langmuir capacity constant and the diffusion coefficients for Henry's law and Langmuir populations decrease by a larger factor than the Henry's law solubility constant. These results can be tentatively interpreted by assuming either a one-phase or two-phase structure for these polyimide films.     

Sorption and partial molar volumes of gases in poly(ethylene-co-vinyl acetate)

Sorption and dilation properties of polymer-gas systems involving poly(ethylene-co-vinyl acetate) and N₂, CH₄, or CO₂, have been investigated at pressures up to 50 atm at temperatures of 10–40°C. Sorption isotherms for low-solubility gases (i.e., CH₄ and N₂) can be described by Henry's law, and those for high-solubility gas (i.e., CO₂) by Flory-Huggins dissolution equation. Dilation isotherms are similar in contour to the corresponding sorption isotherms. From the obtained sorption and dilation data, partial molar volumes of the gases in the polymer were determined as a function of temperature. Thermal expansivity of dissolved CO₂ molecules was estimated at ca. 2.4 × 10^?3°C^?1 from the temperature dependence of partial molar volume. The expansivity is smaller than that of liquid CO₂ and larger than those of the polymer and organic liquids. © 1994 John Wiley & Sons, Inc.     

Permeation of carbon dioxide through homogeneous dense and asymmetric cellulose acetate membranes

Sorption isotherms for carbon dioxide in a homogeneous dense cellulose acetate membrane were measured by the pressure decay method at three temperatures between 20 and 40°C and gas pressures up to 1.7 MPa. Steady-state permeation rates for the same system at three temperatures between 24 and 40°C and gas pressures up to 2.2 MPa were measured by the variable volume method. The equilibrium sorption was described well in terms of the dual-mode sorption model. The pressure dependence of the mean permeability coefficient was interpreted by the total immobilization model, i.e., a limiting case of the dual-mode mobility model, where the diffusion coefficient for the Henry's law mode is not assumed to be constant but depends upon gas pressure via a modified free-volume theory. The observed pressure dependence of the mean permeability coefficient through an asymmetric cellulose acetate membrane was very similar to that through a homogeneous dense membrane. The thin skin layer in the asymmetric membrane can be simulated by a homogeneous dense membrane from the point of view of gas sorption and diffusion.     

Dual-mode analysis of subatomspheric-pressure CO2 sorption and transport in Kapton H polyimide film

Sorption kinetics and equilibria as well as permeabilities and diffusion time lags for CO₂ in Kapton polyimide film have been studied at temperatures from 35 to 55°C and pressures up to 0.78 atm. The sorption/desorption cycles indicate that the diffusivity of CO₂ increases with increasing local penetrant concentration in the polymer. Both the permeability and time lag decrease with increasing upstream CO₂ pressure. All of these results are described well by theoretical expression based on the dual-mode theory of sorption and transport in glassy polymers.     

Dilation of polyethylene by sorption of carbon dioxide

The dilation of low-density polyethylene accompanied by the sorption of CO₂ was measured by microscopy under pressures up to 50 atm at temperatures from 25 to 55°C. The dilatometry measurement, which is also applied to the determination of the thermal expansion coefficient, is directly performed by a cathetometer. The dilation of LDPE by sorbed CO₂ is linear with concentration. The buoyancy correction is described for the CO₂ sorption isotherms in LDPE. The partial molar volume of CO₂ in LDPE, calculated from the dilation and the sorption isotherms, is almost independent of temperature.     

Experimental determination of dissociation constant,Henry's constant,heat of reactions,SO2 absorbed and gas bubble–liquid interfacial area for dilute sulphur dioxide absorption into water

The experimental results for dissociation constant, Henry's constant, heat of reactions and gas bubble–liquid interfacial area for absorption of dilute SO₂ (SO₂ partial pressure upto 0.963 kPa) into water in bubble column are presented. The relations between Henry's constant versus temperature and dissociation constant versus temperature have been proposed based on the present experimental investigation. The temperature dependence on gas bubble–liquid interfacial area per unit volume of liquid has examined. Result shows a very small decrease in interfacial area with increase in temperature. The experimental results are used to correlate total SO₂ absorbed at saturation as function of temperature and SO₂ partial pressure. Comparisons between experimental results and literature data have also been made at different temperatures. The reasonable fittings between the data obtained from correlation and literature data shows that the proposed correlation can be successfully used for predicting the absorption equilibria of dilute SO₂ in distilled water at different temperatures.