CO₂ Selective PolyActive Membrane: Thermal Transitions and Gas Permeance as a Function of Thickness

Abstract

It is generally accepted that the melting point of a semicrystalline polymer is associated with the thickness of the crystalline lamellae (Gibbs-Thomson equation). In this study, a commercially available multiblock copolymer PolyActive composed of 77 wt % of poly(ethylene glycol terephthalate) and 23 wt % of poly(butylene terephthalate) was dip-coated on top of a multilayer microporous support. The thickness was changed between 0.2 and 8 μm using coating solutions containing 0.75-7.5 wt % PolyActive. The surface temperature of the membrane during dip-coating was monitored using an infrared camera. Single gas permeances of N, H, CH, and CO were measured between 20 and 80 °C at temperature steps of 2 °C. Spherulitic superstructures composed of radially directed lamellae were observed in the polarized light microscope in the prepared membranes. Atomic force microscopy studies showed that the thickness of the crystalline lamellae was in the order of 10 nm or 0.01 μm at the surface of the membrane. Therefore, according to the Gibbs-Thomson equation, the melting point should not change in the thickness range 0.2-8 μm. However, the gas permeance data showed that the melting point of the polyether domains of the 0.2 μm PolyActive layer was 10 °C lower compared to that of the 8 μm layer. The results can be explained by considering that the width of many crystalline lamellae significantly reduces as a function of film thickness, thereby reducing the average fold surface free energy/lateral surface free energy ratio.

Effect of Immobilization of Phenolic Antioxidant on Thermo-Oxidative Stability and Aging of Poly(1-trimethylsilyl-1-propyne) in View of Membrane Application

“…High molecular weight polymer cannot penetrate into pores, while the solution is effectively depleted of solvent under the influence of capillary forces. The two processes combined lead to a fast change of polymer state from being dissolved in diluted solution to solid [ 31 ]. The process of solution concentration increase is accompanied by a strong surface temperature decrease.…”

The prospect of synthesis of PES/PEG blend membranes using blend NMP/DMF for CO2/N2 separation

“…Other than gas separation properties, thermal strength and mechanical properties are also affected by casting thickness. According to Rahman et al [196], the thermal resistance of PolyActive membrane increases with casting thickness as the melting point of the thinner PolyActive membrane of 0.2 μm was 10 °C lower than that of its thicker 8 μm counterpart [196]. Therefore, casting thickness should be thoroughly studied as it affects gas separation performance, thermal properties, and mechanical characteristics of the membrane [147].…”

Membrane Separation of Gaseous Hydrocarbons by Semicrystalline Multiblock Copolymers: Role of Cohesive Energy Density and Crystallites of the Polyether Block

“…Multiblock copolymers, which have alternating series of polyether-based soft blocks and a glassy or semicrystalline hard block (e.g., polyamide [ 1 , 2 ], polyester [ 3 , 4 ], polyimide [ 5 ] and polyurethane [ 6 ]), have earned a reputation as ideal membrane materials for gas separation. The structure–property relationships of this class of polymers have been an intriguing field of research in the last decade.…”

“…P2533 is composed of 80 wt% PTMO and 20 wt% polyamide 12 [ 1 , 2 , 18 ]. P1500 and P4000 are composed of 77 wt% poly(ethylene glycol)terephthalate and 23% poly(butylene terephthalate) [ 3 , 17 ]. P1500 and P4000 contain PEO segments of 1500 and 4000 g/mol, respectively.…”