| Polyacrylonitrile(PAN)has the characteristics of anti-oxidation,good chemical stability,cheap and easy availability,and is often used in the preparation of microfiltration,ultrafiltration and nanofiltration membranes.Non-solvent-induced phase inversion(NIPS)is a commonly used method for the preparation of organic polymer membranes.There are few studies on the effect of gel bath residence time and solvent residues on the membrane pore structure during the phase separation process.Thermal crosslinking is a common method for preparing solvent-resistant polymer films.As a thermoplastic material,polyacrylonitrile is a thermoplastic material.When the polyacrylonitrile film is heat-treated above the melting temperature,the pore structure of the film will merge,causing it to penetrate Flux dropped significantly.In this paper,polyacrylonitrile was used as raw material to prepare polyacrylonitrile-based asymmetric membranes by phase inversion method.Polyacrylonitrile solvent-resistant film was modified by sol-gel method and carboxylation method to inhibit the fusion of pore structure of polyacrylonitrile thermally cross-linked film.The influence of nitrile membrane structure and properties,the effects of carboxylation concentration,temperature and time on the structure and properties of polyacrylonitrile membrane were systematically studied.Using the optimized modification method,a high-flux polyacrylonitrile solvent-resistant membrane was prepared,and the following research results were obtained:(1)The polyacrylonitrile-based asymmetric base membrane was prepared by the phase inversion method.The residence time of the gel bath was 1min and 30 s.segregated to the membrane surface in the bath.With the increase of pure water exchange time,the residual amount of DMAc solvent decreases,the membrane becomes gradually densified,the pure water flux gradually decreases,and the hydrophilicity of the membrane also gradually decreases.The residual amount of DMAc solvent was reduced,the mobility of PAN molecular chain was weakened during the thermal cross-linking process,the degree of fusion of the pore structure was reduced,and the degree of densification of the film was reduced.(2)The silica gel modified membrane was prepared by the sol-gel method.With the increase of TEOS concentration,the polymerization degree of the silica gel network increased,the membrane surface became denser,the membrane pore size was smaller,and the water flux of the modified membrane increased.With the increase of BSA rejection,the silica gel surface contains abundant hydroxyl groups,which increases the hydrophilicity of the membrane and decreases the water contact angle.The higher the TEOS concentration,the smaller the shrinkage rate of the PAN film during the thermal crosslinking process,which fully indicates that the silicone gel plays a role in restricting the movement of the polymer segments during the pre-oxidation process and inhibits the shrinkage of the modified film.(3)The PAN-based membrane is compounded on a flexible support to prepare a PANsupported membrane,and the PAN-supported membrane is modified by carboxylation,which promotes cyclization and oxidation of cyano groups in the pre-oxidation stage,and improves the performance of the carboxylated supported membrane.The degree of cross-linking,avoiding the fusion of membrane pores at high temperature,and maintaining the flux of PAN thermally cross-linked membrane,the carboxylation conditions for maintaining the pore structure during the pre-oxidation process of PAN membrane are: carboxylation concentration0.4mol/L,carboxyl group The carboxylation time was 1h,and the carboxylation temperature was 60°C. |
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