Fluoropolymer resin has outstanding characteristics such as low surface energy, good thermal stability, chemical stability, weather resistance, etc. It is widely used in high-performance anti-corrosion, anti-fouling coatings, anti-corrosion lining, packaging film and separation membrane materials and other fields. In particular, polyvinylidene fluoride (PVDF) has been extensively used in the manufacture of ultra- and micro-filtration flat plates and hollow fiber membranes due to its good processing performance, and plays an important role in the treatment of municipal sewage and industrial sewage by the membrane bioreactor (MBR). (Journal of Membrane Science, 2011, 375, 1-27).
Micro- and nano-porous structure control is a key factor in the preparation of high performance (high throughput, narrow pore size distribution, low pollution, etc.) polyvinylidene fluoride microporous membrane. At present, the preparation principle of polyvinylidene fluoride microporous membranes is mainly non-solvent induced phase separation (Nips) and thermally induced phase separation (Tips). Non-solvent induced phase separation methods usually produce large finger holes, while finger holes The existence of the film is disadvantageous to the use intensity of the film, and the penetration of the finger hole increases the probability of the defect on the film surface.
Thermally induced phase separation A microporous membrane with a high interconnected pore structure can be prepared by liquid-liquid phase separation, and usually does not have a dense skin, and due to the higher preparation temperature (usually higher than the melting temperature of PVDF), hydrophilic modification It is more difficult, so the film of this kind of structure is easy to absorb plugging pollution during use, resulting in serious attenuation of flux.
The Functional Membrane Team of the Ningbo Institute of Materials Technology and Engineering of the Chinese Academy of Sciences developed a non-solvent-assisted thermal induced phase separation method (Nat-ips) (Desalination, 2012, 298, 99-105) to prepare a bicontinuous structure with an interpenetrating network. Polyvinylidene fluoride microporous membrane, which is a non-perfect solvent using polyvinylidene fluoride, thermodynamically stable polymer solution at a temperature lower than the melting point of polyvinylidene fluoride, induced polymerization by lowering the temperature and using a non-solvent method Vinylidene fluoride phase separation, and reduce its kinetic phase separation rate, to obtain a narrow pore size distribution, pore size controllable microporous membrane adjustment.
In order to improve its hydrophilicity, in-situ polymerization is further adopted. In the process of phase separation of polyvinylidene fluoride, a hydrophilic polymer network is fixed in the membrane body in one step to obtain a permanently hydrophilic polyvinylidene fluoride. Microporous membranes and improved their antifouling properties (Journal of Materials Chemistry, 2012, 22, 9131-9137).
Based on the above-mentioned phase separation control and in-situ modification methods, recently the team Xue Lixin researcher and Liu Fu associate researcher proposed and developed for the first time a polyvinylidene fluoride microporous with both super-oleophobic and ultra-hydrophobic properties under water. Membranes (contact angles exceeding 150 degrees) were published in the journal Advanced Materials (influence factor 14.892, Adma. 201305112R2, accepted). The membrane can be converted to strong hydrophilic and oleophilic properties in the air (contact angles are close to 0 degrees).
The research group mainly constructed a multi-layered structure with micropores and rafts, and micro-petals and nano-scale microfibrils on the surface of microporous membranes through the composite method of polymer soft template stripping, non-solvent-assisted thermal phase separation and in-situ modification. Structure (as shown in Figure 1). The PVDF microporous membrane has a good separation effect for micro- and nano-scale water-in-oil emulsions and oil-in-water emulsions that are difficult to separate in the chemical industry. The separation purity is over 99.9%, and the effective separation size reaches 20 nm (eg, Figure 2).
The PVDF microporous membrane exhibits unique underwater super-oleophobic/oil-water ultra-hydrophobic intelligent conversion characteristics. After 20 cycles of oil-water separation experiments, a stable operating flux was exhibited (as shown in Figure 3). The membrane can be prepared with a large area and continuous, with good repeatability, and is expected to be used in the degreasing of steel plant wastewater, oil field reinjection water treatment, and various oily solvent water removal treatment and other fields.
This work has applied for 4 Chinese national invention patents and has been supported by the National Natural Science Foundation of China, the “863†Plan and international cooperation projects.
Fig. 1 (a) Experiment of peeling load of PVDF film and non-woven fabric. (bd) Membrane SEM images (200 micron, 20 micron, and 2 micron, respectively)
Fig. 2 Effect of oil-water emulsion separation experiment (a) Water-in-water toluene emulsion (upper) and toluene-water-in-water emulsion (lower image). (bd) Water-in-water chloroform microemulsion (b) Tyndall effect (c) Dynamic light scattering detection Droplet Size distribution (d) Infrared spectra of the solution before and after filtration
Figure 3 (a) Permeate fluxes of oil-in-water and water-in-oil emulsions. (b) Alternating circulation fluxes of toluene-toluene-water-in-water emulsions (c) Large-area high-intensity super-parent/super-sparse conversion poly-bias Fluoroethylene microporous membrane
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