Views: 6 Author: Site Editor Publish Time: 2023-05-26 Origin: Site
With the progress and development of society, people's living standards are getting higher and higher, but with this comes the deteriorating pollution of water resources, especially the pollution of water sources by various organic substances, as a result, the traditional water treatment process of pre-chlorination and oxidation, coagulation and sedimentation, filtration, disinfection and other processes can no longer meet the current water quality requirements, while membrane separation technology has become one of the most concerned water treatment technologies today due to its excellent effluent quality and wide applicability in wastewater reuse projects. Therefore, a lot of research has been conducted on the cost, performance, and post-treatment of water treatment membranes.
The most commonly used polymer materials for water treatment membranes are: polyvinylidene fluoride (PVDF), polysulfone (PSF), polyethersulfone (PES), polyvinyl chloride (PVC), polyamide (PA), polyacrylonitrile (PAN). However, water treatment membranes made directly from these polymer materials have their own defects, such as high manufacturing cost, poor mechanical properties, small water flux, easy contamination and breakage of the membrane and other such defects. Therefore, the search for water treatment membranes with low manufacturing cost, good mechanical properties, high water flux and not easy to contaminate and break is the top priority today. Among the membrane contamination problems, membrane surface modification techniques can be used to enhance the hydrophilicity of the membrane surface to reduce contamination. Surface modification techniques can be used to produce suitable separation membranes with sufficient mechanical strength and effective reduction of membrane contamination. Membrane surface modification techniques mainly include organic grafting membrane modification, plasma polymerization, organic block copolymerization membrane modification, solventization, ion shift gel membrane and blended composite modification, etc. Among them, the research on blended composite modification has attracted more and more attention. This method adds a co-solvent with improved properties to the solvent to improve the compatibility (mutual solubility) of two membrane materials and induces one membrane material to form a film on the surface of another membrane material, so that the interfacial polymers penetrate each other to form a network structure, i.e. interpenetrating polymer network.
1. NVP graft-modified polymeric membrane materials (the study of water treatment membranes made of NVP graft-modified polyvinylidene fluoride (PVDF) is illustrated as an example).
N-Vinylpyrrolidone (NVP) is a monomer of polyvinylpyrrolidone (PVP) and copolymer (PVP/V A), which makes a polymer with good solubility, bio-solubility, chemical stability, low toxicity and film-forming properties, thus making it stand out from chemicals and has a wide range of applications in chemistry, pharmacy and materials. For example, by grafting other polymers (cotton fiber, PET cellulose, rubber, polypropylene film and other polymer films), the monomer NVP has the excellent properties of PVP while retaining their respective properties, thus improving the performance and range of application of each polymer.
Polyvinylidene fluoride (PVDF) is a comprehensive polymer material with good chemical stability and heat resistance, which should be widely used in membrane materials and has wide applications in environmental protection, water treatment, petrochemical, food processing and other fields. However, polyvinylidene fluoride (PVDF) has the disadvantage of hydrophobicity, which limits its application and reduces its cost effectiveness. It has been shown that the hydrophobicity of PVDF is due to the lack of hydrophilic groups in its structure, and the introduction of hydrophilic groups in its structural formula by grafting technique is the most important to improve its performance.
A lot of research has been done on grafted polyvinylidene fluoride (PVDF) materials, such as acrylic acid, methyl methacrylate, acrylamide and other monomers, but the superiority of N-vinylpyrrolidone (NVP), the parent material of polyvinylpyrrolidone (PVP), in various aspects makes the PVDF modified with N-vinylpyrrolidone (NVP) finally stand out. It has not only enabled PVDF to be used in a wider range of applications, but also solved practical problems such as contamination of PVDF filter membranes due to electrostatic charges and low water flux.
2. PVP series co-blended modified polymer film materials (illustrated by co-blending modification study with polyvinyl chloride (PVC)):
It has the advantages of good chemical stability, high mechanical strength, low price and strong acid and alkali resistance, which makes it widely used in the field of membrane separation technology. However, the poor hydrophilicity of PVC material leads to low membrane separation effect, poor anti-pollution ability and great difference between wet and dry membranes (the basic products are wet membranes), while wet membranes have the disadvantages of not being antibacterial, not easy to transport and can only be stored in glycerol, which greatly restricts its application area and value. For this reason, today's research on the application of PVC materials in water treatment membranes is focused on the modification of their hydrophilic properties, and a large number of different schemes have been reported both at home and abroad in this area of co-modification. For example: PVC/VC-CO-V AC (vinyl chloride-vinyl acetate), PVC/CEV A, PVC/CPVC (carboxylated polyvinyl chloride), PVC/SAN (polyethylene-acrylonitrile copolymer), PVC/IB-CO-MIL (isobutylene-maleic anhydride copolymer), PVC/PAN (polyacrylonitrile), PVC/PMMA (poly methyl methacrylate), PVC/PVP (polyvinylpyrrolidone), PVC/PVP-VA (vinylpyrrolidone-vinyl acetate copolymer) and other different blending modification studies. The modified membranes have been used under different conditions and in different fields, and their performance has been improved in various aspects. However, after comparing a large amount of experimental data, it was concluded that under the same conditions (e.g., the same retention rate of the reference material), the PVC material modified with polyvinylpyrrolidone PVP or polyvinylpyrrolidone copolymer PVP-VA series has the best performance in various aspects.
Similarly, there are a large number of reports on the use of polyvinylpyrrolidone PVP to modify other polymer materials, such as modified polysulfone or polyethersulfone made of permanent hydrophilic hollow fiber membrane not only in a large number of applications in wastewater treatment, but also in the field of medical and purification of water on the high-grade membrane to occupy a place.
Polyvinylpyrrolidone PVP series (polyvinylpyrrolidone homopolymer, polyvinylpyrrolidone copolymer, insoluble polyvinylpyrrolidone polymer) has not only made significant contributions to membrane technology in modified materials, but also it is an important pore-making agent for water treatment membranes, and many water treatment membranes in the market are now using polyvinylpyrrolidone PVP series as pore-making agents.
For example, a new field of application of polyvinylpyrrolidone has been opened due to the successful attempt of Dow Chemical Company to modulate the pores of polyvinylidene fluoride (PVDF)-based nanofiltration membranes with polyvinylpyrrolidone. However, the structure of the molecular chain of this polyvinylpyrrolidone used as a porogenic agent is significantly different from that of the conventional polyvinylpyrrolidone. Conventional polyvinylpyrrolidone is a linear polymer obtained by initiating a polymerization reaction in aqueous solution by a redox initiation system. The chain transfer reaction between the chain growth radical and the oxidant is the key to determine the average molecular weight of the polymer. However, because of this, the molecular weight distribution of the polymer is extremely wide, with a distribution index of 5 or more, the pore size distribution of the membrane obtained by using this traditional polyvinylpyrrolidone as a pore-making agent is uneven, the mechanical strength of the membrane is poor, and the water flux is low.
In order to meet the needs of customers, Shandong Tsingrun Chemical has been cooperating with domestic universities and colleges that have expertise in the field of water treatment membrane application research, in order to realize the controllability of PVP production process and prepare new PVP with uniform molecular weight distribution in line with customers' requirements, and we are committed to filling the gaps in this field in China. So far, we have made a major breakthrough in molecular weight distribution. We hope that all the technical people who are committed to this field will call and write to us to discuss and exchange ideas and promote together.
