Li-Feng Fang

Antifouling properties of poly(vinyl chloride) membranes modified by amphiphilic copolymers P(MMA-b-MAA)

Three well-defined diblock copolymers of poly(methyl methacrylate-b-methacrylic acid) (P(MMA-b-MAA)) were synthesized using atom transfer radical polymerization method and varying poly(methacrylic acid) (PMAA) chain lengths. These copolymers were blended with PVC to fabricate porous membranes via phase inversion process. Membrane morphologies were observed by scanning electron microscopy (SEM), and chemical composition changes of the membrane surfaces were measured by X-ray photoelectron spectroscopy (XPS). Static and dynamic protein adsorption experiments were used to evaluate antifouling properties of the blend membranes. It was found that, the blend membranes containing longer PMAA arm length showed lower static protein adsorption, higher water permeation flux and better protein solution flux recovery.

Improving the wettability and thermal resistance of polypropylene separators with a thin inorganic-organic hybrid layer stabilized by polydopamine for lithium ion batteries

This study aims to improve the wettability and thermal resistance of polypropylene (PP) separators for lithium ion batteries. The PP separator was first coated with polydopamine (PDA) on the basis of mussel-inspired surface chemistry. Then a thin inorganic–organic hybrid layer was immobilized onto the PDA-coated separator via a sol–gel process using tetraethoxysilane (TEOS) solutions. This method does not need any commonly-used polymeric binders because of the unique adhesion behaviour of the PDA intermediate layer, which greatly reduces the thickness of the modification layer and avoids excessive pore blocking. Owing to the incorporation of the hybrid layer, the composite separators showed better affinity with the liquid electrolyte and obvious reduction in thermal shrinkage in comparison to the unmodified separator. And the battery performances, such as interfacial resistance, discharge capacity and C-capacity were all improved after modification. Considering the effective adhesion of PDA onto nearly all kinds of separator/membrane surfaces, this modification strategy can be widely used without causing any obvious damage to the mechanical strength of the unmodified separators/membranes.

Improving the properties of HDPE based separators for lithium ion batteries by blending block with copolymer PE-b-PEG

To improve the performances of HDPE-based separators, polyether chains were incorporated into HDPE membranes by blending with poly(ethylene-block-ethylene glycol) (PE-b-PEG) via thermally induced phase separation (TIPS) process. By measuring the composition, morphology, crystallinity, ion conductivity, etc, the influence of PE-b-PEG on structures and properties of the blend separator were investigated. It was found that the incorporated PEG chains yielded higher surface energy for HDPE separator and improved affinity to liquid electrolyte. Thus, the stability of liquid electrolyte trapped in separator was increased while the interfacial resistance between separator and electrode was reduced effectively. The ionic conductivity of liquid electrolyte soaked separator could reach 1.28 × 10−3 S·cm−1 at 25°C, and the electrochemical stability window was up to 4.5 V (versus Li+/Li). These results revealed that blending PE-b-PEG into porous HDPE membranes could efficiently improve the performances of PE separators for lithium batteries.

Poly（N,N-dimethylaminoethyl methacrylate） Grafted Poly（vinyl chloride）s Synthesized via ATRP Process and Their Membranes for Dye Separation

To functionalize poly(vinyl chloride) (PVC) for various applications, monomers containing tertiary amine group are incorporated into PVC via atom transfer radical polymerization (ATRP) initiated by the labile chlorines in their backbones. The kinetics of synthesis was carefully investigated, and it is proven that the grafting polymerization process can be effectively controlled by regulating the reaction time. The membranes are fabricated using PVC and copolymers by non-solvent induced phase separation (NIPS) process. The hydrophilicity and pore structure of copolymer membranes were enhanced as well, these membranes are endowed with positive charge. When PDMA% (i.e., the PDMA weight percentage in copolymer) is 31.1%, the flux and Victoria blue B rejection are 26.0 L·m-2·h-1 (0.5 MPa) and 91.2%, respectively. Thus, the newly synthesized polymer is proven to be a promising material for dye separation with positive charges.

Preparation of robust braid-reinforced poly(vinyl chloride) ultrafiltration hollow fiber membrane with antifouling surface and application to filtration of activated sludge solution

Braid-reinforced hollow fiber membranes with high mechanical properties and considerable antifouling surface were prepared by blending poly(vinyl chloride) (PVC) with poly(vinyl chloride-co-poly(ethylene glycol) methyl ether methacrylate) (poly(VC-co-PEGMA)) copolymer via non-solvent induced phase separation (NIPS). The tensile strength of the braid-reinforced PVC hollow fiber membranes were significantly larger than those of previously reported various types of PVC hollow fiber membranes. The high interfacial bonding strength indicated the good compatibility between the coating materials and the surface of polyethylene terephthalate (PET)-braid. Owing to the surface segregation phenomena, the membrane surface PEGMA coverage increased upon increasing the poly(VC-co-PEGMA)/PVC blending ratio, resulting in higher hydrophilicities and bovine serum albumin (BSA) repulsion. To compare the fouling properties, membranes with similar PWPs were prepared by adjusting the dope solution composition to eliminate the effect of hydrodynamic conditions on the membrane fouling performance. The blend membranes surface exhibited considerable fouling resistance to the molecular adsorption from both BSA solution and activated sludge solution. In both cases, the flux recovered to almost 80% of the initial flux using only water backflush. Considering their great mechanical properties and antifouling resistance to activated sludge solution, these novel membranes show good potential for application in wastewater treatment.

Tailoring the surface pore size of hollow fiber membranes in the TIPS process

A new method was used to tailor the surface pore size of PVDF hollow fiber membranes in the TIPS process by the co-extrusion of different solvents at the outer layer of the extruded polymeric solution. In this method, the membrane properties can be controlled over a wide range of mean pore size (from 24 to 600 nm), water permeability (from 3 to more than 4000 L m−2 h−1 bar−1), and acceptable particle rejection (from 50 to 500 nm), with only a slight change in the membrane mechanical strength. Ternary interaction between the extruded solvent, polymer, and diluent in the polymer dope solution played a major role in controlling the hollow fiber membrane properties. At the interface of the extruded solvent and polymeric solution, segregation of the diluent or PVDF molecules near the outer skin layer of hollow fiber membrane strongly affected the mean pore size and filtration performance over a wide range, from MF membranes to typical UF membranes. Considering the competitive solubility difference between the extruded solvent and the diluent in the polymeric solution and that of PVDF, a road map has been shown for the selection of a satisfactory extruded solvent to obtain membranes with desired properties.

Poly(vinylidene difluoride)/poly(tetrafluoroethylene-co-vinylpyrrolidone) blend membranes with antifouling properties

To inhibit fouling phenomenon in membrane process, a new amphiphilic copolymer, poly(tetrafluoroethylene-co-vinylpyrrolidone) (P(TFE-VP)), was blended with poly(vinylidene difluoride) (PVDF) to fabricate a series of antifouling membranes via non solvent induced phase separation (NIPS) method. The effect of copolymer blend ratios and TFE/VP ratios on membrane properties were evaluated, and the stability of P(TFE-VP) in PVDF membrane was studied. The membrane morphology was controlled by adjusting polymer concentration in dope solution, such that all membranes have similar pore size and density, as well as pure water permeability. In evaluating the effect of TFE/VP ratios, the content of VP in dope solutions was also adjusted to allow a fair comparison. We found that for P(TFE-VP) with a higher VP content, adsorption of BSA on polymer film was negligible. Higher blend ratios of this copolymer resulted in higher surface VP content and better hydrophilicity, but antifouling performance ceased to improve when blend ratio was larger than 1:9 (copolymer:PVDF). Meanwhile, a lower VP content in copolymer resulted in inferior hydrophilicity and severe fouling of the blend membranes. It was also proved that comparing with PVP homopolymer, P(TFE-VP) had satisfying stability inside PVDF membrane.

One-step fabrication of polyamide 6 hollow fibre membrane using non-toxic diluents for organic solvent nanofiltration

We developed new polyamide 6 hollow fibre membranes using a green process to fabricate cutting-edge “organic solvent nanofiltration” membranes by one-step spinning process for organic solvent separation. This economic and sustainable membrane showed good rejection and durability performance in various organic solvents.

Tailoring both the surface pore size and sub-layer structures of PVDF membranes prepared by the TIPS process with a triple orifice spinneret

In this study, the surface and sub-layer structures of poly(vinylidene fluoride) (PVDF) membranes were effectively tailored by extruding different types of solvents at the outer layer of the polymer solution with a triple-orifice spinneret using the thermally induced phase separation (TIPS) process. The segregation of the diluent or PVDF chains to the interface between the extruded solvent and polymer solution was exploited to tailor the membrane surface structure. In contrast, the diffusion of extruded solvents having good compatibility with PVDF into the polymer solutions changed the phase separation mechanism and resulted in the formation of a novel composite-like structure (spherules connected by the bicontinuous network structure) in the sub-layer of the membrane. This membrane structure enhanced the permeation stability drastically. The membrane properties and structures are summarized based on the change in the competitive ternary interactions between the polymer, diluent, and extruded solvent, and could be used as a guide for selecting appropriate solvents to design and tailor membranes with desired structures and properties.

Dual Superlyophobic Aliphatic Polyketone Membranes for Highly Efficient Emulsified Oil–Water Separation: Performance and Mechanism

Efficient treatment of difficult emulsified oil-water wastes is a global challenge. Membranes exhibiting unusual dual superlyophobicity (combined underwater superoleophobicity and underoil superhydrophobicity) are intriguing to realize high-efficiency separation of both oil-in-water and water-in-oil emulsions. For the first time, a robust polymeric membrane demonstrating dual superlyophobicity to common apolar oils was facilely fabricated via a simple one-step phase separation process using an aliphatic polyketone (PK) polymer, thanks to a conjunction of intermediate hydrophilicity and re-entrant fibril-like texture upon the prepared PK membrane. Further chemical modification to improve surface hydrophilicity slightly can enable dual superlyophobicity to both apolar and polar oils. It is found that a nonwetting composite state of oil against water or water against oil was obtainable on the membrane surfaces only when the probe liquids possess an equilibrium contact angle (θow or θwo) larger than the critical re-entrant angle of the textured surfaces (73°), which can explain the existences of dual superlyophobicity and also the nonwetting to fully wetting transitions. A simple design chart was developed to map out the operational windows of material hydrophilicity and re-entrant geometry, that is, a possible zone, to help in the rational design of similar interfacial systems from various materials. Switchable filtrations of oil-in-water and water-in-oil nanoemulsions were achieved readily with both high flux and high rejection. The simplicity and scalability of the membrane preparation process and the well-elucidated underlying mechanisms illuminate the great application potential of the PK-based superwetting membranes.