Preparation Of PVDF Membrane Modified By Hyperbranched Polysiloxane And Study On Oil-water Separation Performance

With the rapid development of economy,the discharge of industrial wastewater and domestic sewage is increasing,resulting in a massive amount of oily wastewater inevitably entering water bodies,which has caused serious damage to the ecological environment.Membrane separation technology has attracted much attention in the field of water treatment due to its advantages of high separation efficiency,low cost,small footprint and simple operation.However,the surface of traditional membrane materials is easily polluted by oil droplets,which leads to the attenuation of membrane permeability flux and the reduction of membrane service life,limiting the application of membrane separation technology in oily wastewater treatment.Therefore,it is of great significance to develop efficient and environmentally friendly anti-fouling membrane materials by means of modulating the chemical composition and microstructure of the membrane surface based on the study of the special infiltrative surfaces in nature.Hyperbranched polysiloxane（HBPSi）is a highly branched polymer with backbone of-Si-O-Si-chains,and it has sufficient nanocavity and a large number of easily functionalized terminal amino groups,which can not only achieve demulsification,but also form a strong hydration layer on the membrane surface to resist oil droplet pollution.Therefore,in this thesis,new anti-fouling membrane materials were prepared by grafting HBPSi onto the surface of polyvinylidene fluoride membrane（PVDF）through different methods to achieve efficient separation of oil-in-water emulsions.The changes of microscopic morphology,chemical composition and surface wettability of PVDF membranes before and after modification were studied,and the oil-water separation performance and anti-fouling performance of the membranes were further investigated.The details of the study are as follows:1.Preparation of hyperbranched polysiloxane grafted polyvinylidene fluoride membrane and study on oil-water separation performanceThe membrane surface was modified by changing the chemical composition.Specifically,hyperbranched polysiloxane grafted polyvinylidene fluoride membrane（HBPSi-g-PVDF）was prepared through grafting amino-terminated hyperbranched polysiloxanes onto the PVDF membrane surface via an amidation reaction.The surface morphology and chemical composition of HBPSi-g-PVDF membrane were tested and analyzed by various characterization methods,and the wettability and anti-fouling properties of the membrane were investigated.The results showed that the HBPSi-g-PVDF membrane possessed superhydrophilic/underwater superoleophobic properties and excellent resistance to oil droplet adhesion.The water flux of HBPSi-g-PVDF membrane reached up to 16924 L·m^-2·h^-1·bar^-1 and the flux recovery rate was higher than 99.0%.In addition,the HBPSi-g-PVDF membrane exhibited high separation efficiency（>99.1%）for different types of oil-water emulsions with permeation flux of more than 6000 L·m^-2·h^-1·bar^-1.At the same time,HBPSi-g-PVDF membrane also showed excellent environmental durability and recyclability,maintaining stable performance even in acid,alkaline and salt chemical environments.2.Preparation of zwitterionic hyperbranched polysiloxane@poly（dopamine）@poly（vinylidene fluoride）membrane and study on oil-water separation performanceTo improve the anti-fouling performance of the membrane,the hydration capacity of the membrane surface modification layer is improved by zwitterionic functionalization.The zwitterionic hyperbranched polysiloxane@polydopamine@polyvinylidene fluoride membrane（ZHBPSi@PDA@PVDF）was prepared by surface modification of PVDF membrane through polydopamine deposition,which was used as a chemical reaction platform to graft amino-terminated hyperbranched polysiloxane via Michael addition reaction,followed by zwitterionic functionalization using the reaction of terminal amino with 1,3-propanesulfonate lactone.The surface structure and chemical composition of ZHBPSi@PDA@PVDF membrane were analyzed by various characterization methods,and the wettability and anti-fouling properties of the membrane surface were investigated.The results showed that the surface of ZHBPSi@PDA@PVDF membrane achieved superhydrophilic modification and the underwater oil contact angle reached 158.6°.In addition,ZHBPSi@PDA@PVDF membrane possessed excellent self-cleaning and anti-fouling properties,which can effectively resist the adhesion and contamination of crude oil.Moreover,the membrane showed high water flux of 13924 L·m^-2·h^-1·bar^-1 and achieved excellent separation of oil-in-water emulsions with emulsion permeation flux and separation efficiency of 5534 L·m^-2·h^-1·bar^-1and 99.9%,respectively,as well as exhibited superior recycling performance.Meanwhile,ZHBPSi@PDA@PVDF membrane can achieve effective separation of crude oil emulsion with permeation flux of 3986 L·m^-2·h^-1·bar^-1and separation efficiency of 98.3%,which provides a new idea for the treatment of high-viscosity oil-containing wastewater.3.Preparation of hyperbranched polysiloxane@tannic acid—3-aminopropyltriethoxysilane@polyvinylidene fluoride membrane and study on oil-water separation performanceConsidering both surface roughness and chemical composition,the superhydrophilic modification of PVDF membrane was realized by constructing rough multi-level micro and nano structures and introducing a significant number of hydrophilic groups on the surface.The hyperbranched polysiloxane@tannic acid—3-aminopropyltriethoxysilane@polyvinylidene fluoride membrane（HBPSi@TA-APTES@PVDF）with hyperhydrophilic/underwater hyperoleophobic properties was prepared by grafting hyperbranched polysiloxane through Michael addition reaction between terminal amino groups and tannic acid on the surface of TA-APTES rough coating,which was formed by the interaction between annic acid（TA）and 3-aminopropyltriethoxysilane（APTES）.The surface structure and chemical composition of HBPSi@TA-APTES@PVDF membrane were analyzed by various characterization methods,and the wettability and anti-fouling properties of the membrane surface were investigated.The results showed that HBPSi@TA-APTES@PVDF membrane possessed excellent anti-fouling and recycling properties.Furthermore,the membrane exhibited superior separation performance in oil-water separation process,with pure water flux and emulsion permeation flux of 24781 L·m^-2·h^-1·bar^-1 and 6586 L·m^-2·h^-1·bar^-1,respectively.And the separation efficiency of HBPSi@TA-APTES@PVDF membranes for different emulsions was as high as 99.9%.The multistage layered structure and abundant amino groups on the surface of HBPSi@TA-APTES@PVDF membrane endow the membrane with excellent anti-crude oil adhesion performance and outstanding separation effect on crude oil emulsion,with separation efficiency and permeation flux reaching 99.2%and 5590 L·m^-2·h^-1·bar^-1,respectively.In addition,HBPSi@TA-APTES@PVDF membrane features excellent chemical corrosion resistance which leads to promising applications.