Membrane Cross-section Morphology Research Articles

Poly(benzimidazole)/poly(vinylphosphonic acid) blend membranes with enhanced performance for high temperature polymer electrolyte membrane fuel cells

PBI:PVPA (Poly(benzimidazole):poly(vinylphosphonic acid)) polymer electrolyte membranes were fabricated with several molar ratios and number-average molecular weights (M¯n) of PVPA. Inter-polymer interactions and cross-section morphology of membranes were analyzed using FT-IR and scanning electron microscopy, respectively. Water uptake, proton conductivity, and methanol permeability of the membranes were characterized at several operating conditions. In addition, the influence of doping level of phosphoric acid (H3PO4) on the membranes proton conductivity was investigated. The membranes proton conductivities were enhanced with PVPA molar ratio and M¯n. The highest proton conductivity at 150 °C, 79.6 mS.cm−1, was obtained for H3PO4-doped PBI:PVPA membrane containing PVPA with M¯n of 42,000 g.mol−1, PBI:PVPA molar ratio of 1:1 and H3PO4 doping level of 15.2. Proton hopping between PBI and PVPA was found to be the most dominant proton transport mechanism through the PBI:PVPA membranes, especially at anhydrous state. Finally, the results suggest that these membranes are promising candidates for high-temperature proton exchange membrane fuel cell applications.

Influence of different non-solvent additives to the casting solution on the structure and properties of PES membranes

The effect of the precipitation value (PV) of mixtures of strong and weak non-solvent additives (NSA) on the phase state and viscosity of polyethersulfone(PES)/dimethylacetamide(DMAc)/non-solvent solutions and on the structure and performance of PES membranes were studied. Polyethylene glycol 400 (PEG-400, PV > 1000), water (PV = 10.6), 85 % phosphoric acid (PV = 13.0), glycerol (Gly, PV = 27.8) and mixtures thereof were used as NSA for PES-DMAc solutions. Using Gly/PEG-400 mixtures it was established that the increase in PV of NSA leads to the increase of a miscibility gap on the phase diagram. At a constant concentration of Gly/PEG-400 mixture, the viscosity of the solutions decreases. For a constant ratio (0.94–0.95) of the NSA amount added to the polymer-solvent system to the NSA amount causes a phase separation of the casting solution (coagulation value) increase in PV of NSA Gly/PEG-400 leads to an increase of the membrane pure water flux (PWF) from 13 up to 150 l/m2 h at 1 bar. The most dramatic increase in PWF occurs in the range of PV 39.7–125 g/dL. The results of SEM study don’t show significant differences in the cross-section morphology of membranes for different PV of NSA. However, the thickness of the selective membrane layer increases from 1 up to 4.5 μm when PV increased from 39.7 up to 750 g/dL. Thus, these studies allow us to conclude that the structure and properties of ultrafiltration membranes depend not only on the coagulation value of the casting solution, but also on the precipitation value of NSA.

Preparation and Characterization of TiO2-LaFeO3 based Mixed Matrix Membrane for Oily Wastewater Treatment

The aim of this study was to investigate the effects of catalyst loading in mixed matrix membrane. LaFeO3 and TiO2-LaFeO3 were synthesized by sol-gel glucose method. Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), contact angle, membrane permeation testing unit and UV-Vis spectrophotometer techniques are used for characterization. FTIR showed the successful transformation of photocatalyst TiO2, LaFeO3 and TiO2-LaFeO3. Due to increase in nanoparticles loading, the hydrophilicity of the membrane had improved thus increase the permeation flux. The cross-section morphology of membranes (PTL-1, PTL-3 and PTL-4) indicated that all the membranes were found to have asymmetric structure, consisting of dense top layer (air side), a porous sublayer (finger-like) and a small portion of sponge-like bottom surface layer (glass side). But as for the PTL-2, the cross sections of the membranes have a fully sponge-like structure. The formation of sponge-like structure was associated to the slow solidification process during the casting. The highest oily wastewater rejection was 76.26% with highest permeation flux and lower contact angle. This result showed that nanoparticles with membrane had improved the oily wastewater rejection. It proved that the fabricated nanoparticles with mixed matrix membrane exhibits a high flux, which is 2 to 3 orders of magnitude higher than commercial filtration membranes with an acceptable separation performance.

Surface fluorination of polyamide nanofiltration membrane for enhanced antifouling property

A new kind of fluorinated polyamine was successfully synthesized and grafted onto the polyamide membrane surface to fabricate an antifouling nanofiltration membrane with low surface free energy. The surface composition of the fluorinated polyamide nanofiltration membrane was confirmed by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The membrane cross-section morphology was observed by a field emission scanning electron microscopy (FESEM). The presence of perfluoroalkyl groups on the membrane surface significantly lowered the surface free energy from 60.0 to 44.4mJ/m2. The filtration experiment results indicated that the surface fluorination did not lower the separation performance of the polyamide nanofiltration membrane significantly. The antifouling experiment results demonstrated that the fluorinated polyamide nanofiltration membranes exhibited superior antifouling property, that is, high flux recovery ratio (~98.5%) and low total flux decline ratio (~11%) during protein aqueous solution and humic acid aqueous solution filtration.

Preparation of PVDF hollow fiber ultrafiltration membrane via phase inversion/chemical treatment method

Poly(vinylidene fluoride) (PVDF) hollow fiber membranes were prepared via a phase inversion/chemical treatment method, using N,N-dimethylacetamide (DMAc) as solvent, Calcium carbonate as inorganic additive, and water and HCl as coagulation media. Effects of external coagulation bath and bore fluid composition on membrane performance were investigated by using scanning electron microscopy, mechanical properties, porosity, average bubble point pressure, and permeation performance. The results show that: (1) The cross-section morphology of membranes have no significant change, exhibiting a two-layer finger-like structure extended to the middle of the cross-section. (2) The roughness of the external surface increased considerably and the number of the surface pores increased as well when we introduced HCl as the second coagulation. The permeation experiments reveal that acid treatment had no impact on fibers which had precipitated completely. (3) The number and pore size underlying the inner skin layer increased when bore fluid changed from DI water to 10% acetic acid, leading to the decrease of porosity and tensile strength. Moreover, the pure water flux increased from 360 to 580 L/(m2 h) without the significant change of BSA rejection. The PVDF/CaCO3 membranes prepared from the dope with 10% acetic acid as the bore fluid and 1 mol/L HCl as second coagulation bath had the best ultrafiltration performance.

GRAFTING POLY(N-ISOPROPYL ACRYLAMIDE) FROM POLY(VINYLIDENE FLUORIDE) MIROFILTRATION, MEMBRANES VIA DIRECT SURFACE-INITIATED, ATOM TRANSFER RADICAL POLYMERIZATION, AND TEMPERATURE SENSITIVITY

Well-defined poly(N-isopropyl acrylamide) (PNIPAAm) brushes on commercial hydrophobic poly(vinylidene fluoride) (PVDF) microfiltration membrane surfaces were prepared, via direct atom transfer radical polymerization (ATRP) with the secondary fluorinated site of PVDF as initiator and water as solvent at 80°C. The effect of solvents on the ATRP was studied in detail. The water as reaction solvent was in favor of surface-initiated ATRP of N-isopropyl acrylamide (NIPAAm) from secondary fluoride of PVDF membranes. The chemical composition and structure of the modified PVDF membrane surfaces were determined by attenuated total reflectance (ATR) Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The surface and cross-section morphology of membranes were studied by scanning electron microscopy (SEM). The pore sizes of the pristine PVDF membrane and the PNIPAAm-grafted PVDF membranes were measured using micro-image analysis and process software. The introduction of the well-defined PNIPAAm on the PVDF membrane gave rise to hydrophilicity. Water contact angles of PVDF membranes reduced after the surface grafting of PNIPAAm. Water fluxes and protein solution permeation experiments revealed that the PNIPAAm-grafted PVDF membranes exhibited temperature-responsive permeability. The unique microstructure of PNIPAAm brushes facilitated hydrophilicity below the lower critical solution temperature.

Controlled grafting from poly(vinylidene fluoride) microfiltration membranes via reverse atom transfer radical polymerization and antifouling properties

A reverse atom transfer radical polymerization (RATRP) with benzoyl peroxide (BPO)/CuCl/2,2-bipyridine (Bpy) was applied onto grafting of poly(methyl methacrylate) (PMMA) and poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA) from poly(vinylidene fluoride) (PVDF) microfiltration (MF) membrane surfaces, including the pore surfaces. The introduction of peroxide and hydroperoxide groups onto the PVDF membranes was achieved by ultraviolet (UV) irradiation in nitrogen, followed by air exposure. RATRP from UV pretreated hydrophobic PVDF membranes was then performed for attaching well-defined homopolymer. The chemical composition of the modified PVDF membrane surfaces was characterized by attenuated total reflectance (ATR) FT-IR spectroscopy and X-ray photoelectron spectroscopy (XPS). The surface and cross-section morphology of membranes were studied by scanning electron microscopy (SEM). The pore sizes of the pristine PVDF and the PMMA grafted PVDF membranes were measured using micro-image analysis and process software. With increase of graft concentration, the pore size of the modified membranes decreased and became uniform. Kinetic studies of homogeneous (in toluene solution) system revealed a linear increase in molecular weight with the reaction time and narrow molecular weight distribution, indicating that the chain growth from the membrane surface was a “controlled” or “living” grafting process. The introduction of the well-defined PMMA on the PVDF membrane gave rise to hydrophilicity. Protein adsorption and protein solution permeation experiments revealed that the UV pretreated hydrophobic PVDF membrane subjected to surface-initiated RATRP of methyl methacrylate (MMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) exhibited good antifouling property.