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In gas separation membrane processes, CO2 may induce the plasticization of glassy polymer, lowering its the mechanical rigidity and reducing the glass transition, with a loss of separation performances. Such mechanism is often associated to gas permeability behavior in glassy membranes vs. upstream p, and increasing trends are considered as the footprint of the plasticization onset. However, there is no clear correlation between gas permeability and the effects of CO2 on mechanical behavior. The CO2 induced plasticization in glassy membranes is investigated by direct DMA analysis of polymers saturated at different CO2 pressures. Matrimid polyimide is considered, as it shows a non-monotonous CO2 permeability behavior, and compared to PS (decreasing behavior) and PMMA (increasing). CO2 lowed the elastic modulus of all materials investigated, while the relaxation dynamics revealed a strong enhancement of tan δ, even in absence of a second order transition. The same qualitative behaviors are observed for all glassy systems investigated, and in Matrimid, no apparent change is identified around the pressure value corresponding to the minimum in CO2 permeability, excluding the presence of a new phenomenon onset. Results suggest that increasing permeability behaviors and non-monotonous trends, are not directly related to softening effect induced by CO2 in the polymer matrix, and such features have to be ascribed to the combination of solubility and diffusivity coefficients. [ABSTRACT FROM AUTHOR]

The alignment of polymer chains is a well known microstructural evolution effect due to straining of polymers. This has a drastic influence on the macroscopic properties of the initially isotropic material, such as a pronounced strength in the loading direction of stretched films. For modeling the effect of strain induced anisotropy a macroscopic constitutive model is adopted in this paper. As a key idea, weighting functions are introduced to represent a strain-softening/hardening-effect to account for induced anisotropy. These weighting functions represent the ratio between the total strain rate (representing the actual loading direction) and a structural tensor (representing the stretched polymer chains). In this way, material parameters are used as a sum of weighted direction related quantities. In the finite element examples we simulate the cold-forming of amorphous thermoplastic films below the glass transition temperature subjected to different re-loading directions. [ABSTRACT FROM AUTHOR]

In this work we evaluated the sorption, diffusion and permeation of a series of volatile organic compounds (VOCs) (acetone, n-butane, n-pentane, n-hexane, ethanol, methanol, chloroform and toluene) into glassy polymers of increasing fractional free volume (FFV): Polycarbonate (PC), Amorphous Teflon AF1600 and AF2400, poly-trimethylsilyl norbornene (PTMSN) and poly[1-(trimethylsilyl)-1-propyne] (PTMSP). Based on some experimental data of sorption and diffusion, and on theoretical and empirical models for the solubility and diffusion coefficients, the permeability for vapor/N2 mixtures was evaluated. These parameters are useful for the membrane separation processes and for other applications such as chemical sensors. The ideal separation factors of glassy polymeric membranes versus mixtures of VOCs and N2 were estimated at various pressures and compositions and at 25° C. The selectivity vs. permeability maps for the mixtures considered were plotted, showing that some of these materials show potentially the same selective ability of rubbery polymeric films. In particular it is shown that, the higher the FFV, the better the vapor/gas selectivity. [ABSTRACT FROM AUTHOR]