Hydrophilic and anti-fouling PVDF blend ultrafiltration membranes using polyacryloylmorpholine-based triblock copolymers as amphiphilic modifiers

Influence of hydrophilic block length on the aggregation properties of polyglycidol-polystyrene-polyglycidol copolymers

Amphiphilic triblock copolymers, polyglycidol-polystyrene-polyglycidol (PGL-PS-PGL), were synthesised via anionic polymerization starting from the synthesis of a polystyrene macroinitiator with 60 styrene units in the block terminated by ethylene oxide. Poly(ethoxyethyl glycidyl ether) blocks of different lengths were created on both sides of the macroinitiator. By removing the ethoxyethyl blocking groups, PGL-PS-PGL copolymers containing polyglycidol blocks with DP 11, 23, 44 and 63 were received. Their structures were determined by NMR and FTIR. The hydrophilicity of PLG-PS-PGL films was studied upon exposure to water vapour. To perform the copolymers' aggregation in water, the samples were dialysed from DMF into water. The critical concentration of their micellisation (CMC) was determined by measuring the absorbance of the 1,6-diphenylhexa-1,3,5-triene (DPH) probe and the intensity of light scattered by the copolymers' solution as a function of concentration. CMC values increased with increasing the number of hydrophilic glycidol units in the copolymer chain. The sizes of aggregates formed slightly above the critical concentration were measured by dynamic light scattering (DLS), and particles were imaged by cryo-TEM. Cryo-TEM pictures showed the presence of regular micelles in copolymer dispersions. For copolymers with shorter PGL chains aggregated partices were detected. Moreover, cryo-TEM demonstrated that the copolymers with a polyglycidol block of DP = 63 formed regular spherical micelles that formed 2D ordered organisation on the surface. X-ray measurements showed the formation of a partially crystallised PS core in the micelle's interior. The aggregates of all copolymers were stable. Their sizes did not change after one year of storage. The particles did not disassociate even after diluting their dispersions to a concentration 10 times lower than the critical concentration.

Fluorine-Containing, Self-Assembled Graft Copolymer for Tuning the Hydrophilicity and Antifouling Properties of PVDF Ultrafiltration Membranes

Neat poly(vinylidene fluoride) (PVDF) ultrafiltration (UF) membranes exhibit poor water permeance and surface hydrophobicity, resulting in poor antifouling properties. Herein, we report the synthesis of a fluorine-containing amphiphilic graft copolymer, poly(2,2,2-trifluoroethyl methacrylate)-g-poly(ethylene glycol) behenyl ether methacrylate (PTFEMA-g-PEGBEM), hereafter referred to as PTF, and its effect on the structure, morphology, and properties of PVDF membranes. The PTF graft copolymer formed a self-assembled nanostructure with a size of 7-8 nm, benefiting from its amphiphilic nature and microphase separation ability. During the nonsolvent-induced phase separation (NIPS) process, the hydrophilic PEGBEM chains were preferentially oriented towards the membrane surface, whereas the superhydrophobic PTFEMA chains were confined in the hydrophobic PVDF matrix. The PTF graft copolymer not only increased the pore size and porosity but also significantly improved the surface hydrophilicity, flux recovery ratio (FRR), and antifouling properties of the membrane. The membrane performance was optimal at 5 wt.% PTF loading, with a water permeance of 45 L m-2 h-1 bar-1, a BSA rejection of 98.6%, and an FRR of 83.0%, which were much greater than those of the neat PVDF membrane. Notably, the tensile strength of the membrane reached 6.34 MPa, which indicated much better mechanical properties than those reported in the literature. These results highlight the effectiveness of surface modification via the rational design of polymer additives and the precise adjustment of the components for preparing membranes with high performance and excellent mechanical properties.

Micromechanism Study of Molecular Compatibility of PVDF/PEI Blend Membrane

In this paper, the compatibility of polyetherimide (PEI) with different contents as a high-performance copolymer and polyvinylidene fluoride (PVDF) was studied, and 5%-20% PEI was prepared by the non-solvent-induced phase inversion method. The compatibility of PVDF and PEI was evaluated by analyzing the physical structure and properties of the blend membrane, the microstructure, the glass transition temperature Tg, the enthalpy, and the mechanism of the polymer blend enthalpy change. The results show that the blend membranes have -NH and C=O-N binding energies at X-ray photoelectron spectroscopy (XPS), which preliminarily proves that fluorine-amine bonds are formed between the polymers, and new spectra appeared by Fourier transform infrared (FTIR) and X-ray diffraction (XRD) peaks, which further proves that the two have the formation of fluorine-amine bonds, the Tg and enthalpy of the mixed membrane was increased, and a scanning electron microscope (SEM) observed that the membrane pores changed from finger-like pores to sponge-like macropores. When the content of PEI is 15%, the performance of the blended membrane is the best, the water contact angle increases to 58.5°, the porosity increases to 17.33%, the maximum force increases to 8.04 N, and the elongation at break decreases to 24.26%, the pure water flux is 1870.292 L/m²·h, and the oil rejection is 87%. In addition, the enthalpy change of polymer blending further proves that PEI and PVDF are compatible systems and have a good performance improvement for PVDF.

Hydrophilic and Positively Charged Polyvinylidene Fluoride Membranes for Water Treatment with Excellent Anti-Oil and Anti-Biocontamination Properties

Membrane fouling limits the rapid development of membrane separations. In this study, a blend membrane containing polycationic liquid (P(BVImBr₁-co-PEGMA₁)) is presented that can improve the antifouling performance of polyvinylidene fluoride (PVDF) membranes. By mixing the polycationic liquid into PVDF, an improved membrane-surface hydrophilicity and enlarged membrane porosity were detected. The water contact angle decreased from 82° to 67°, the porosity enlarged from 7.22% to 89.74%, and the pure water flux improved from 0 to 631.68 L m⁻² h⁻¹. The blend membrane surfaces were found to be always positively charged at pH 3~10. By applying the membranes to the filtration of oil/water emulsion and bovine serum albumin (BSA) solution, they showed a very high rejection rate to pollutants in wastewater (99.4% to oil droplets and 85.6% to BSA). The positive membrane surface charge and the increased membrane hydrophilicity resulted in excellent antifouling performance, with the flux recovery rates of the dynamic filtration tests reaching 97.3% and 95.5%, respectively. Moreover, the blend membranes demonstrated very low BSA adhesion and could even kill S. aureus, showing excellent antifouling properties.

Antifouling improvement of a polyacrylonitrile membrane blended with an amphiphilic copolymer

The amphiphilic copolymer polyacrylonitrile-co-poly(hydroxyethyl methacrylate) (PAN-co-PHEMA) was readily blended with polyacrylonitrile (PAN) to fabricate a flat-sheet blending membrane through non-solvent induced phase separation (NIPS). In the membrane-forming process, the hydrophilic PHEMA chains are uniformly distributed on the surface, as revealed by the energy-dispersive X-ray tests. The sponge-like sub-layer embedded with droplet-shaped structures is formed at the cross-sections of membranes, because of the high viscosity of the casting solution. With the increase of copolymer concentration, the mean pore size of the blending membranes increases from 26.9 to 99.8 nm, leading to the increase of membrane flux from 93.6 to 205.4 l/(m2h). The incorporation of PAN-co-PHEMA copolymer endows the blending membrane with a rough surface microstructure and enhanced hydrophilicity. The rejection ratio of membranes for emulsified pump oil reaches 99.9%, indicating a prominent separation performance. In the cycle permeation experiments, the flux recovery ratio of the blending membranes is as high as 99.6%, which is much higher than those of PAN membrane. The irreversible fouling of blending membranes induced by oil adsorption is alleviated, and converted into reversible fouling, owing to the reduction of the adhesion force between foulant and membrane surface. These results suggest that the anti-fouling property of PAN membranes has been dramatically strengthened via the addition of PAN-co-PHEMA copolymer.

Statistical Analysis of Synthesis Parameters to Fabricate PVDF/PVP/TiO2 Membranes via Phase-Inversion with Enhanced Filtration Performance and Photocatalytic Properties

Non-solvent induced phase-inversion is one of the most used methods to fabricate membranes. However, there are only a few studies supported by statistical analysis on how the different fabrication conditions affect the formation and performance of membranes. In this paper, a central composite design was employed to analyze how different fabrication conditions affect the pure water flux, pore size, and photocatalytic activity of polyvinylidene fluoride (PVDF) membranes. Polyvinylpyrrolidone (PVP) was used to form pores, and titanium dioxide (TiO₂) to ensure the photocatalytic activity of the membranes. The studied bath temperatures (15 to 25 °C) and evaporation times (0 to 60 s) did not significantly affect the pore size and pure water flux of the membranes. The concentration of PVDF (12.5 to 17.5%) affected the viscosity, formation capability, and pore sizes. PVDF at high concentrations resulted in membranes with small pore sizes. PVP affected the pore size and should be used to a limited extent to avoid possible hole formation. TiO₂ contents were responsible for the decolorization of a methyl orange solution (10^-5 M) up to 90% over the period studied (30 h). A higher content of TiO₂ did not increase the decolorization rate. Acidic conditions increased the photocatalytic activity of the TiO₂-membranes.

Fabricating novel PVDF-g-IBMA copolymer hydrophilic ultrafiltration membrane for treating papermaking wastewater with good antifouling property

Ultrafiltration membranes are widely used for the treatment of papermaking wastewater. The antifouling performance of polyvinylidene fluoride (PVDF) ultrafiltration membranes can be improved by changing the hydrophilicity. Here, a novel amphiphilic copolymer material, PVDF grafted with N-isobutoxy methacrylamide (PVDF-g-IBMA), was prepared using ultraviolet-induced Cu(II)-mediated reversible deactivation radical polymerization. The amphipathic copolymer was used to prepare ultrafiltration membrane via NIPS. The prepared PVDF-g-IBMA ultrafiltration membrane was estimated using ¹H NMR, FT-IR, and DSC. The contact angle, casting viscosity, and the permeation performance of the PVDF-g-IBMA ultrafiltration membrane were also determined. The pure water flux, bovine serum albumin removal rate, and pure water flux recovery rate of the PVDF-g-IBMA ultrafiltration membrane were 432.8 L·m^-2·h^-1, 88.4%, and 90.8%, respectively. Furthermore, for the treatment of actual papermaking wastewater, the chemical oxygen demand and turbidity removal rates of the membrane were 61.5% and 92.8%, respectively. The PVDF-g-IBMA amphiphilic copolymer ultrafiltration membrane exhibited good hydrophilicity and antifouling properties, indicating its potential for treating papermaking wastewater.

Design of a novel poly(aryl ether nitrile)-based composite ultrafiltration membrane with improved permeability and antifouling performance using zwitterionic modified nano-silica

Zwitterionic nano-silica (SiO₂ NPs) obtained by lysine surface modification was used as a hydrophilic inorganic filler for preparing a poly(aryl ether nitrile) (PEN) nanocomposite membrane via an immersion precipitation phase inversion method. The effects of zwitterionic SiO₂ NPs addition on the morphology, separation and antifouling performance of the synthesized membranes were investigated. Zwitterionic surface modification effectively avoided the agglomeration of SiO₂ NPs. The PEN/zwitterionic SiO₂ NPs composite membranes exhibited improved porosity, equilibrium water content, hydrophilicity and permeability due to the introduction of hydrophilic SiO₂ NPs in the casting solution, and the optimal pure water flux was up to 507.2 L m⁻² h⁻¹, while the BSA rejection ratio was maintained at 97.4%. A static adsorption capacity of 72.9 μg cm⁻² and the FRR up to 85.3% in the dynamic antifouling experiment proved that the introduction of zwitterionic SiO₂ NPs inhibited irreversible fouling and enhanced the antifouling ability of the PEN membrane.

Zwitterionic nano-silica (SiO₂ NPs) obtained by lysine surface modification was used as a hydrophilic inorganic filler for preparing a poly(aryl ether nitrile) (PEN) nanocomposite membrane via an immersion precipitation phase inversion method.