Influence of microstructural variations on morphology and separation properties of polybutadiene-based polyurethanes

Polybutadiene-based polyurethanes with different cis/trans/1, 2-vinyl microstructure contents are synthesized. The phase morphology and physical properties of the polymers are investigated using spectroscopic analysis (FTIR and Raman), differential scanning calorimetry (DSC), X-ray scattering (WAXD and SAXS) and atomic force microscopy (AFM). In addition, their gas transport properties are determined for different gases at 4 bar and 25 °C. Thermodynamic incompatibility and steric hindrance of pendant groups are the dominant factors affecting the morphology and properties of the PUs. FTIR spectra, DSC, and SAXS analysis reveal a higher extent of phase mixing in high vinyl-content PUs. Moreover, the SAXS analysis and AFM phase images indicate smaller microdomains by increasing the vinyl content. Smaller permeable soft domains as well as the lower phase separation of the PUs with higher vinyl content create more tortuous pathways for gas molecules and deteriorate the gas permeability of the membranes

Influence of Blend Composition and Silica Nanoparticles on the Morphology and Gas Separation Performance of PU/PVA Blend Membranes

Polymer blending and mixed-matrix membranes are well-known modification techniques for tuning the gas separation properties of polymer membranes. Here, we studied the gas separation performance of mixed-matrix membranes (MMMs) based on the polyurethane/poly(vinyl alcohol) (PU/PVA) blend containing silica nanoparticles. Pure (CO2, CH4, N2, O2) and mixed-gas (CO2/N2 and CO2/CH4) permeability experiments were carried out at 10 bar and 35 °C. Poly(vinyl alcohol) (PVA) with a molecular weight of 200 kDa (PVA200) was blended with polyurethane (PU) to increase the CO2 solubility, while the addition of silica particles to the PU/PVA blend membranes augmented the CO2 separation performance. The SEM images of the membranes showed that the miscibility of the blend improved by increasing the PVA contents. The membrane containing 10 wt % of PVA200 (PU/PVA200–10) exhibited the highest CO2/N2~32.6 and CO2/CH4~9.5 selectivities among other blend compositions, which increased to 45.1 and 15.2 by incorporating 20 wt % nano-silica particles

Pore-networked membrane for trace-level molecular separations in environmental water

The wide presence of pharmaceuticals and personal care products (PPCPs) in water is a major concern regarding current emerging pollution and urges their selective monitoring to establish water quality management. Microporous materials have been developed to extract organic contaminants and further embedded as fillers into polymeric composites like matrix-mixed membranes (MMMs) for practical use. Considering the relatively large molecular size of PPCPs and their slow diffusion in the membrane, the MMM configuration is, however, inadequate for liquid-phase separations. Here we report pore-networked membranes (PNMs) based on the concept of interconnecting the microporous fillers within the polymer matrix to form a continuous porous phase. Linked metal-organic polyhedra (MOP) network is designed for the continuous porous phase with tunable micro/mesopores, which are accessible for big PPCP molecules to facilitate their diffusion and adsorption. By contrast to MMMs, PNMs show enhanced stability, capacity and extraction selectivity towards specific pharmaceutical drugs amongst 13 PPCPs in environmental water matrices at trace-level concentrations

Overcoming humidity-induced swelling of graphene oxide-based hydrogen membranes using charge-compensating nanodiamonds

Graphene oxide (GO) can form ultrapermeable and ultraselective membranes that are promising for various gas separation applications, including hydrogen purification. However, GO films lose their attractive separation properties in humid conditions. Here we show that incorporating positively charged nanodiamonds (ND+s) into GO nanolaminates leads to humidity-resistant, yet high-performing, membranes. While native GO membranes fail at a single run, the GO/ND+ composite retains up to ~90% of GO’s H2 selectivity against CO2 after several cycles under an aggressive humidity test. The addition of negatively charged ND to GO brought no such stabilization, suggesting that charge compensation acts as the main mechanism conferring humidity resistance, where ND+s neutralize the negative charge GO sheets. We observed a similar but inferior stabilization effect when positively charged polyhedral oligomeric silsesquioxane replaces ND+. The demonstrated material platform offers a solution for separating H2 gas from its usually humid mixtures generated from fossil fuel sources or water splitting