Preparation And Properties Of Antibacterial Polyvinylidene Fluoride Separation Membranes

Textile printing and dyeing wastewater has the characteristics of large amount of water,deep color,high organic content and complex composition.It is very difficult to treat,which is one of the urgent problems to be solved in the textile printing and dyeing industry.Membrane separation technology has the advantages of low energy consumption,high efficiency,low cost,convenient operation,mild conditions,low environmental requirements,wide processing capacity,and environmental protection.It can be used to treat textile printing and dyeing wastewater with complex components and high treatment difficulty.Polyvinylidene fluoride（PVDF）membrane has the advantages of high mechanical strength,high temperature resistance and chemical corrosion resistance.It is a common organic separation membrane,but its hydrophobicity leads to easy contamination in the separation process,affecting its permeability and service life.Therefore,the modification of PVDF membrane has become a research hotspot for many researchers.In this paper,PVDF membrane was taken as the main research object.The modified membranes and the composite membrane with excellent performance were prepared by coating modification method,non-solvent induced phase separation method and electrospinning method,respectively.The specific research contents are as follows:First,PVDF membrane was prepared by coating modification method.The commercial PVDF microporous membrane was modified by hydrogel coating which was prepared by acrylic acid（AA）,acrylamide（AM）and chitosan（CS）.The AA in the hydrogel coating was chlorinated to give PVDF membrane antibacterial properties.The prepared hydrogel coating modified PVDF membranes had good hydrophilicity and underwater oleophobicity.The water contact angles of the P（AA-co-AM）/PVDF membrane and the P（AA-co-AM）/CS/PVDF membrane were 58.0°and 16.4°,respectively,the underwater oil contact angles were 125.3°and 143.30°,respectively.The pure water flux of the P（AA-co-AM）/PVDF membrane and the P（AA-co-AM）/CS/PVDF membrane were 6519 L?m^-2?h^-1?bar^-1 and 3616 L?m^-2?h^-1?bar^-1respectively.In addition,the P（AA-co-AM）/PVDF membrane and the P（AA-co-AM）/CS/PVDF membrane had certain separation performance for toluene emulsion,copper sulfate solution and methylene blue solution.Moreover,the chlorinated P（AA-co-AM）/PVDF membrane and the chlorinated P（AA-co-AM）/CS/PVDF membrane had good antibacterial properties,and could kill all inoculated S.aureus and E.coli within 30 min and 1 min,respectively.Second,the hydrogel coating was easy to fall off during the use and cleaning process due to the low binding fastness between the hydrogel coating and the commercial PVDF microporous membrane in the first part.In order to solve the problem,the modified PVDF membrane was prepared by non-solvent induced phase separation in the second part.In this part,CS and 1-chloro-2,2,5,5-tetramethyl-4-imidazolidinone（MC）which was one of the N-halamine antibacterial agent were used to prepare modified PVDF membranes with good hydrophilicity,separation performance and antibacterial properties by physical blending.The prepared PVDF@CS@MC membrane had certain hydrophilicity and underwater oleophobicity.The water contact angle was 48.3°,the underwater oil contact angle was 119.7°,and the pure water flux was 2017 L?m^-2?h^-1?bar^-1.In addition,the separation efficiencies of PVDF@CS@MC membrane for mud,toluene emulsion,copper sulfate solution and methylene blue solution had been improved to a certain extent,and the separation fluxes of mud,copper sulfate solution and methylene blue solution had also been significantly improved,which was increased to about 3 times that of the PVDF membrane.Moreover,the PVDF@CS@MC membrane had excellent antibacterial properties,which could kill all the inoculated E.coli in only 1 min and all the inoculated S.aureus in 5 min.Third,the fracture stress of the modified PVDF membrane prepared by non-solvent induced phase separation method after adding chitosan in the second part will be significantly reduced.In order to solve the problem,the PVDF@MC/PAN@MC composite fiber membrane with Janus structure,certain separation performance and antibacterial performance was prepared by electrospinning method using polyacrylonitrile（PAN）,PVDF and MC which is one of the N-halamine antibacterial agent in the third part.The top layer of the PVDF@MC/PAN@MC composite fiber membrane had good hydrophobicity and underwater lipophilicity.The water contact angle of the surface reached to 132.6°,and when the oil droplets fell on the membrane which was immersed in the deionized water,the oil droplets spread rapidly.The bottom layer of the PVDF@MC/PAN@MC composite fiber membrane had good hydrophilicity and underwater oleophobicity.When the water droplets fell on the surface of the membrane,the water droplets spread within 5 s,and the underwater oil contact angle reached to 143.0°.Compared with the PVDF fiber membrane,the pure water flux of the PVDF@MC/PAN@MC composite fiber membrane was also increased,which was 91L?m^-2?h^-1 without any external force.Since the PVDF@MC/PAN@MC composite fiber membrane had a double-layer structure with large performance differences,its separation performance was affected by both the top PVDF@MC fiber membrane and the bottom PAN@MC fiber membrane.Therefore,the separation flux of the PVDF@MC/PAN@MC composite fiber membrane was between the PVDF fiber membrane and the PAN fiber membrane,higher than the PVDF fiber membrane and less than the PAN fiber membrane.Thanks to the composite double-layer structure,the separation efficiency of PVDF@MC/PAN@MC composite fiber membrane was higher than that of PVDF fiber membrane and PAN fiber membrane.Moreover,the PVDF@MC/PAN@MC composite fiber membrane had certain antibacterial properties,and its top and bottom surfaces could kill all the inoculated bacteria when exposed to S.aureus and E.coli for 30 min.In addition,compared with the PVDF fiber membrane,the fracture stress of the PVDF@MC/PAN@MC composite fiber membrane did not change much,even slightly increased,and the elongation at break increased significantly.