ABSTRACT Following our preceding review article in 2000 [1], we principally discussed the sorption and diffusion behavior for CO2 in glassy polymer membranes near the glass transition temperature. The plasticization effect of sorbed CO2 on both the sorption and diffusion processes tends to be brought about in glassy polymer membranes near the glass transition temperature. The behavior was simulated based on the concept that only one population of sorbed CO2 molecules of plasticizing ability to the polymer should exist; a gas-polymer-matrix model proposed by Raucher and Sefcik [5] combined with the sorption theory of Mi et al. [3]. Thereat, the glass transition temperature is depressed by a concentration of sorbed CO2 of plasticizing ability. The simultaneous deviation from the conventional dual-mode sorption and mobility model was observed in cases of CO2 in poly(4-methyl-1-pentene) membrane (PMP, glass transition temperature of pure polymer Tg = 34oC) at 20oC, in polystyrene membrane (PS, Tg = 95oC) at 60oC and 70oC and in cellulose triacetate membrane (CTA, Tg = 80oC) at 50oC and 60oC. The sorption and permeation behavior influenced by the plasticization action of sorbed CO2 molecules for these systems, could be simulated well by the above combined model. Next, the sorption and permeation behavior for CO2 in NH3-plasma-treated and untreated PS membranes at 40oC was analyzed by the proposed combined model. The pressure dependencies of mean permeability coefficients for CO2 in both NH3-plasma-treated and untreated PS membranes at 40oC, being considerably lower than the glass transition temperature of pure polymer (95oC), for CO2 pressures below 0.9 MPa, could also be simulated in terms of the proposed combined model. Above 0.9 MPa, a plasticization action of sorbed CO2 had an influence on the diffusion process rather than on the sorption one, like in the system of CO2 - NH3-plasma-treated and untreated poly (methyl methacrylate) (PMMA, Tg = 105oC) membranes at 30oC and CO2 - NH3-plasma-treated and untreated CTA membranes at 30oC. The pressure dependencies of mean permeability coefficients for the latter system (CO2 in both NH3-plasma-treated and untreated CTA membranes at 30oC) can qualitatively be described by the proposed combined model.
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