Functional Modification And Properties Of PVDF Hollow Fiber Membrane

Polyvinylidene fluoride(PVDF)membrane has excellent physical and chemical properties and separation properties,and has been widely used in the field of water treatment.However,the surface hydrophobic properties of the surface tend to adhere to organic matter,microorganisms,etc.,thereby causing membrane fouling,reducing the service life of the membrane and increasing operating costs.Therefore,the hydrophilic modification of PVDF membranes has very important scientific and practical significance.Ultrasonic technology can significantly enhance the reaction rate,increase the reaction yield and regulate the structure of the polymer in polymer synthesis and modification.Therefore,the functional modification of PVDF hollow fiber membranes was studied by ultrasonic assisted graft polymerization to improve the hydrophilicity and anti-pollution properties of the membrane surface.The main research contents are as follows:PVDF-g-AA hollow fiber membrane was prepared by the technique of ultrasonic assisted graft polymerization.The effects of ultrasonic time,ultrasonic power,monomer concentration and initiator loading on grafting density were discussed in detail.It can realize the regulation of the grafting density of acrylic acid on the surface of the membrane.It was found that the water contact angle of the surface of the modified membrane decreased from 95.72°to 41.40°compared with the pristine membrane,indicating that the hydrophilicity was significantly improved.The pure water flux of the modified membrane was from 245.78±18.97L/m~2·h increased to 359.27±24.66 L/cm~2·h,which increased by 46.18%.The anti-pollution performance of the modified membrane was also significantly improved,and the flux recovery rate(FRR)increased from 52.75±2.76%to 96.29±3.86%.PVDF-g-GMA hollow fiber membrane surface was prepared by the technique of ultrasonic assisted graft polymerization.The effects of ultrasonic time,ultrasonic power and monomer concentration on the grafting density of the membrane surface were discussed in detail.The grafting density of the membrane surface can be controlled to introduce a reactive group epoxy functional group for further functionalization of the modified membrane.It is found that the water contact angle of the membrane surface decreases from 95.72°to 70.27°as compared with the pristine membrane,indicating that the hydrophilicity of the surface of the modified membrane is to some extent.Improvements have been made;the water flux of the modified membrane has also increased to some extent,from 245.78±18.97 L/m~2·h to 319.21±39.97 L/m~2·h.The zwitterionic structure was successfully constructed on the surface of the modified membrane by inducing a ring opening reaction of the epoxy functional group with different amino acids.It was found that the optimum ring-opening reaction temperature was 55°C.Compared with the unmodified membrane,the water contact angle of the surface of the modified film decreased from 95.72°to 0°when reacted with threonine or alanine.;pure water flux increased from245.78±18.97 L/m~2·h to 766.85±19.40 L/m~2·h and 733.04±16.95 L/m~2·h,respectively;the modified membrane showed excellent anti-pollution performance and flux recovery.The rate of FRR increased from 50.12±3.10%to 96.01±1.48%and 95.34±2.22%,respectively.At the same time,the modified membrane also has excellent oil-water separation ability,and the retention rate of oil in the oil-water emulsion is as high as 99.99%.