Hailiang Liu

Fabrication and properties of poly(ethylene chlorotrifluoroethylene) membranes via thermally induced phase separation (TIPS)

Poly(ethylene chlorotrifluoroethylene) (ECTFE) porous membranes have been fabricated via thermally induced phase separation (TIPS). Dioctyl adipate (DOA) as the diluent, micro-scale SiO2 particles and a composite powder (composed of soluble and insoluble particles) as the additives were used in this study. The filtration performance of the prepared membranes was characterized in terms of pure water flux, porosity, mean pore size, water contact angle, mechanical strength, and ultrafiltration tests. The morphologies of the obtained membranes were observed by a scanning electron microscope (SEM). The results showed that ECTFE membranes were a kind of homogeneous membrane, the addition of SiO2 particles and the composite powder brought about interfacial microvoids (IFMs) and a dissolved pore structure. The porosity, pure water and protein solution fluxes decreased, while the rejection ratio and mechanical properties increased with the increase of polymer content. With the addition of additives, the ultrafiltration performance improved obviously. Moreover, the membranes showed good resistance to the aggressive chemical corrosive solutions.

Fabrication and properties of polyvinyl chloride hollow fiber membranes plastified by dioctyl phthalate

ABSTRACT Polyvinyl chloride (PVC) hollow fiber membranes were prepared by twin-screw extrusion method. Dioctyl phthalate (DOP) as the plasticizer was used in this study. The influence of stretching and DOP weight fraction on morphology and performance were investigated. The membranes were characterized by scanning electron microscope, pure water flux, mean pore size measurement, and mechanical strength test. The results show that the PVC hollow fiber membrane was a kind of homogeneous membrane. The pure water flux increased with the theoretical draw ratio and the DOP weight fraction increment. The plastic deformation ratio increased with the theoretical draw ratio increment, but decreased with the DOP weight fraction increment. The deformation-recovery ratio was governed by the DOP weight fraction and was slightly controlled by theoretical draw ratio. Both stretching and increment of DOP weight fraction could increase the mean pore size. At the same time, the tensile strength increased and the elongation ...

Poly(vinylidene Fluoride-Hexafluoropropylene) Porous Membrane with Controllable Structure and Applications in Efficient Oil/Water Separation

Poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) porous membranes are fabricated via thermally induced phase separation (TIPS) with mixed diluent (dibutyl phthalate (DBP)/dioctyl phthalate (DOP)). The effects of mixed diluent are discussed in detail in term of morphology, mean pore size, selective wettability, etc. The results show that the membrane structure changes from spherulitic to bicontinuous with the change of DBP/DOP ratio. It is also found that the degree of crystallization decreases with the decrease of DBP/DOP ratio in mixed diluent. When liquid–liquid (L-L) phase separation precedes solid–liquid (S-L) phase separation, the obtained membranes have outstanding hydrophobicity and lipophilicity, excellent mechanical property. Additionally, the PVDF-HFP hybrid membranes are prepared with silica (SiO2) particles and the effect of SiO2 content on structure and properties is discussed. It is found that the PVDF-HFP hybrid membrane with 2 wt % SiO2 (M3-S2) has better properties and higher filtration rate and separation efficiency for surfactant-stabilized water-in-oil emulsion separation. Moreover, the membrane M3-S2 also exhibits excellent antifouling performance for long-running.

Study on the structural design and performance of novel braid-reinforced and thermostable poly(m-phenylene isophthalamide) hollow fiber membranes

Novel braid-reinforced (BR) and thermostable poly(m-phenylene isophthalamide) (PMIA) hollow fiber membranes comprising reinforced braids and a separation layer were prepared by a dry–wet spinning process for the first time. The effects of PMIA concentration and the braid composition on the structure and performance of the BR PMIA hollow fiber membranes were investigated. Field emission scanning electron microscopy (FESEM) was used to observe the morphologies of the BR PMIA hollow fiber membranes. An increase in PMIA concentration resulted in an increase of the protein rejection rate and a decrease in the pure water flux. The higher flux recovery rate indicated that the BR PMIA membranes had excellent antifouling property compared to commercial PVDF membranes. In the BR PMIA membranes existed favorable interfacial bonding between the separation layer and the reinforced braids as the tensile strength of the BR PMIA membranes exceeded 170 MPa. Moreover, when the operating temperature was increased from 25 °C to 90 °C, the water flux increased more than two-fold with stable ink solution rejection, which showed an excellent thermal stability.

Study on the fabrication and properties of FEP/SiO2 hybrid flat-sheet membrane and its application in VMD

AbstractDue to the chemical structure of the perfluoro group, perfluoro-polymers, such as polytetrafluoroethylene and poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) deserves excellent properties of outstanding thermal and chemical resistance and strong hydrophobicity. In this study, FEP hybrid flat-sheet membranes were fabricated by the melt-compressed membrane formation system, which composed of FEP, micro-scale SiO2, and Dioctyl-Phthalate (DOP). Effects of DOP and SiO2 contents on the membrane morphologies and properties were investigated, respectively. The membranes’ corresponding microfiltration performances were characterized in terms of pure water flux, mechanical strength, membrane porosity, and vacuum membrane distillation (VMD). Results illustrated that the obtained FEP flat-sheet membranes displayed a typical asymmetric structure. There were obvious enhancement of membrane’s pure water flux and porosity with increasing DOP and SiO2 contents. The salt rejections achieved as high as 99.9% ...

Study on poly(tetrafluoroethylene- co -hexafluoropropylene) hollow fiber membranes with surface modification by a chemical vapor deposition method

In this paper, poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) hollow fiber membranes, for applications in water purification, were prepared by a melt-spinning method with FEP as the polymer matrix, water-soluble composite powder as the pore-forming agent and dioctyl phthalate (DOP) as the diluent. Then, a layer of polypyrrole (PPy) was deposited on the surface of the FEP hollow fiber membranes by a chemical vapor deposition method. The microstructures and acid/alkali resistance properties of the FEP/PPy composite hollow fiber membranes were investigated. The results showed that the as-prepared FEP hollow fiber membranes had a multi-microporous structure of stretched pores, interfacial pores and dissolved pores. The sponge-like pore structure was distributed homogeneously over the cross-section of the membrane, which brought about a larger pure-water flux. The polymerization of the pyrrole deposit on the surface of the FEP hollow fiber membranes brought about the improvement of hydrophilicity while the reduction of membrane pore size further resulted in the increase of rejection. The acid/alkali resistance results indicated that the un-deposited FEP hollow fiber membranes had excellent acid and alkali resistance, whereas the alkali resistance was weak after PPy deposition.

Fabrication of tubular braid reinforced PMIA nanofiber membrane with mussel-inspired Ag nanoparticles and its superior performance for the reduction of 4-nitrophenol

A novel tubular braid reinforced (TBR) PMIA/CA-PEI/Ag nanofiber membrane for application in dynamic catalysis was introduced in this study. The preparation method of the TBR PMIA/CA-PEI/Ag nanofiber membrane was facile and efficient. The TBR PMIA/CA-PEI/Ag nanofiber membrane was characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and thermal gravimetric analysis (TGA). The mechanical properties were evaluated by a universal material testing machine. The tensile strength of TBR nanofiber membrane exceeded 500 MPa, whereas that of the nanofiber membrane without reinforcement was merely 10 MPa. Besides, the compressive strength of the TBR nanofiber membrane was also reinforced, which indicated that the TBR nanofiber membrane could withstand a higher operating pressure. The reduction of 4-NP to 4-AP was selected as the model reaction to evaluate the catalytic property of TBR PMIA/CA-PEI/Ag nanofiber membrane. The apparent rate constant of dynamic catalysis was 34.58 times higher than that of static catalysis. After 10 cycles, the conversion of 4-NP was still higher than 95.3%. This indicated that the TBR PMIA/CA-PEI/Ag nanofiber membrane had superior stability and recyclability. Besides, the TBR PMIA/CA-PEI/Ag nanofiber membrane also showed superior catalytic performance when it was used for catalyzing other environmental pollutants.

Effect of stretching on continuous oil/water separation performance of polypropylene hollow fiber membrane

In this work, polypropylene (PP) hollow fiber membranes were fabricated by thermal-induced phase separation method. The influence of cold-stretched and hot-stretched treatment on the morphology and permeability of the PP hollow fiber membranes was investigated. The results showed that there were cracks and crystalline particulate structures on the outer and inner surfaces of the stretched PP hollow fiber membranes, which were not isolated but linked together through fiber-like connections. Compared to the original PP hollow fiber membrane, the mean pore sizes, the porosities, the hydrophobicity and water entry pressure of the stretched PP hollow fiber membranes improved significantly. When applied in conjunction with a vacuum system, the PP hollow fiber membranes could continuously remove oils from water surface, and separate surfactant-free and surfactant-stabilized water-in-oil emulsions, as well. The initial kerosene fluxes of the hot-stretched PP hollow fiber membrane were higher than that of the membranes prepared from original PP hollow fibers or cold-stretched PP hollow fibers. The permeate fluxes of the hot-stretched PP hollow fiber membrane for all different emulsion separations were higher than those of the original PP hollow fiber membrane. There could be seen no emulsion droplet in the optical micrographs after separation, indicating that the water-in-oil emulsions were effectively separated in one-step method.

Preparation and Properties of Two-Dimensional Braid Heterogeneous-Reinforced Polyvinylidene Fluoride Hollow Fiber Membrane

The two-dimensional braid heterogeneous-reinforced (BHR) polyvinylidene fluoride (PVDF) hollow fiber membranes which include PVDF polymer solutions (coating layer) and the two-dimensional braid as a reinforcement were prepared through the dry-wet spinning process. The influence of PVDF concentration in polymer solutions on performance of BHR hollow fiber membranes were investigated by terms of pure water flux, protein rejection, a mechanical strength test, and morphology observations by a scanning electron microscope (SEM). The results of this study indicated that the tensile strength of the BHR PVDF hollow fiber membranes was nearly 75 MPa and the hollow fiber membranes were endowed with better flexibility performance. The BHR PVDF hollow fiber membranes had a favorable interfacial bonding between the coating layer and the two-dimensional braid. The pure water flux decreased, while the rejection ratio increased with the increase of polymer concentration.

Effect of Ethanol Composition in Water Coagulation Bath on Structure and Performance of Homogeneous-Reinforced Polyvinyl Chloride Hollow Fiber Membranes

Homogeneous-reinforced (HR) polyvinyl chloride (PVC) hollow fiber membranes consisting of coating layer and matrix layer were fabricated via coating process. The mixtures of polymer solutions were uniformly coated on the homogeneous PVC matrix membrane which was prepared by melt-spinning method. The influences of ethanol composition in water coagulation bath on structure and performance of HR membranes were investigated. The results showed that the pure water flux of the HR PVC hollow fiber membranes increased with the increase of ethanol weight fraction in coagulation bath, while the porosity changed slightly. The increase of ethanol weight fraction in coagulation bath brought about the decrease of the protein permeation flux and rejection rate. The tensile strength of HR PVC hollow fiber membranes was about 9.5 MPa, while the elongation at break was higher than 97 %.