Modeling of the Sorption and Swelling Behavior of Semicrystalline Polymers in Supercritical CO₂

Abstract

The effect of semicrystallinity on the sorption and swelling behavior of polymers in supercritical CO 2 is investigated. In particular, the experimental behavior measured for four different polymers in a previous work, i.e., poly(methyl methacrylate), poly(vinylidene fluoride), poly(tetrafluoroethylene), and the copolymer tetrafluoroethylene-perfluoromethylvinyl ether, is modeled using four different thermodynamic approaches: the Sanchez-Lacombe method in its nonequilibrium and equilibrium version, a modification of the latter for cross-linked polymers, and the statistical association fluid theory (SAFT) approach. The four considered polymers have an increasing crystallinity from 0% (poly(methyl methacrylate)) to about 50% (poly(vinylidene fluoride)). The results in terms of sorption and swelling are compared and the parameter evaluation procedure is discussed. It is observed that the nonequilibrium Sanchez-Lacombe method performs better than the others in describing the semicrystalline polymers at least from a qualitative point of view. This supports the interpretation that semicrystallinity induces a nonequilibrium effect, since the polymer structure, made more rigid from the presence of the crystallites, does not recover the original compactness after sorption of CO 2 .

Partial Molar Volumes and Thermal Expansion Coefficients as an Explanation for Co-Solvent Effect of Penetrants in Multicomponent Polymer Mixtures

“…It can be observed that the average PMV of each gaseous component increases as its gas phase concentration decreases. However, the PMV dependence on gas phase concentration is higher for CH 4 than n-C4 which can be attributed to the higher interactions of CH 4 with the PDMS matrix (as indicated by the highly negative k 13 value in Figure 1-3 ) compared to n-C4. In addition, the temperature dependence of PMV is more pronounced for n-C4 than CH 4 probably due to higher thermal expansion of n-C4 than CH 4 (see the α values reported above).…”

“…Once the mass fraction, m i , of each gas (or penetrant) in the polymer and the reduced mixture density, ρ , are calculated by solving the SL EoS, the mixture density, ρ , can be estimated by Equation ( 4) [ 3,4,31,33 ] …”

“…[ 3 ] Signifi cantly, this indicates that the proposed methodology can be used for the estimation of PMVs in binary and multicomponent gas/polymer mixtures under different conditions. Finally, the average PMV of CH 4 and n-butane in PDMS can be correlated with their gas phase composition in the temperature range of 25-50 °C using Equation ( 8) for CH 4 and Equations ( 9) where, x is the mass fraction of CH 4 in the gas phase. It should be noted that fi tted SL EoS values can be sensitive to the binary interaction parameters and pure component characteristic parameters used.…”

“…[ 1,[3][4][5][6][7][8][9][10][11][12][13] The PMVs of various gases (or penetrants) in binary gas(1)/polymer(2) mixtures have been estimated for different polymers using experimental dilation, sorption or densimetry data, and hyper-parallel tempering osmotic ensemble techniques. [ 1,2,[4][5][6][7][10][11][12][13][14][15][16] Ternary mixtures (i.e., gas(1)/gas(2)/polymer (3)) represent a simple case of realistic multicomponent systems and, despite of the fact that multicomponent gases/polymer mixtures are very common in polymerization reactors and in the downstream processing units, only few studies have been conducted to estimate or analyze the PMV of the individual species present in such systems. For example, the only known work related to the PMVs of two simultaneously sorbing gases in a single polymer phase was done by Freeman and co-workers, [ 17 ] in which the authors experimentally measured the solubility of pure methane (CH 4 ), pure n-butane (n-C 4 H 10 ), and their mixtures in poly(dimethylsiloxane) (PDMS) at different temperatures and pressures.…”

Solubility of carbon dioxide and cosolvents in a photoresist polymer

“…Spectroscopic studies have revealed the presence of a complex between poly(methyl methacrylate) and carbon dioxide. 4 The photoresist polymer, which has the same polymethacrylate backbone, could also form a complex with CO 2 that changes the interactions in the polymer-cosolvent systems. It is also possible that the presence of the cosolvents in the polymer enhanced the solubility of the CO 2 .…”