Preparation Of PVDF Membrane Doped With Polyethylene Glycol/chitosan And Study On Filtration Performance Of Waterworks

This paper mainly studies the preparation and characterization of polyvinylidene fluoride(PVDF)membrane,and the filtration performance of the prepared membrane to a Water plant.This research topic takes PVDF as the raw material for membrane preparing,polyethylene pyrrolidone(PVPK30)as the porogen,polyethylene glycol 200(PEG200),polyethylene glycol 400(PEG400),polyethylene glycol 600(PEG600),Mixed additives(M-A)and chitosan(CS)were used to adjust the membrane pore structure and improve the hydrophilicity of the membrane surface,and the N,N-dimethyl acetamide was used as a good solvent.PVDF flat and hollow fiber membranes were prepared by non-solvent induced phase separation(NIPS).The effects of different hydrophilic modifiers and additives on the properties of flat and hollow fiber membranes were investigated.Using rotary rheometer,scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),contact Angle measurement instrument to characterize the membrane structure and hydrophilicity.The permeability and antifouling performance of the membrane were tested by the self-assembled flux testing equipment in the laboratory.the research topic is mainly includes three aspects.Firstly,the PVDF membrane was prepared via NIPS.The effect of PEG/M-A on membrane structure and properties was investigated.Polyethylene glycol(PEG200,PEG400,PEG600)is used as porogen,then the membrane pore structure is adjusted by the M-A?M-A,composed of MAA/DMAc/TEP:1:80:20(wt.%)?made in the laboratory.The results exhibit that with the increase of PEG molecular weight,pure water flux of the membrane is up to 1200.5 L·m²·h^-1(MPEG600-0).The PVDF membrane cross section finger-like pore structure changed from irregular to regular;the retention ratio(R)and flux recovery ratio(FRR_B)of MPEG400-5 membrane are89.0%and 87.0%,respectively,and the flux is slightly reduced(415.3 L·m²·h^-1).It was found that PEG/M-A was beneficial to slow down the fouling of bovine serum protein(BSA),and the PVDF membrane prepared by PEG/M-A has a good removal effect on turbidity and UV₂₅₄ of the influent treated in different process sections of a Water plant.Secondly,through the first part of the exploration found that compared with PEG200and PEG400,PEG600 is a better hydrophilic modifier and porogen.In this part,the preparation of PVDF membrane with PEG600 and CS as hydrophilic additive was studied to improve the membrane permeability and antifouling performance.The membrane was fabricated by the NIPS.SEM was accustomed to prove the presence of CS in the polymer matrix.The surface characteristics and structure of the prepared membrane were analyzed,including:pore size distribution,porosity,contact angle and wettability.The addition of CS increased the permeation flux of the membrane,and The highest pure water flux of the modified membrane is 1368.2 L·m²·h^-1(M-0.5),which decreased the water contact angle of the membrane.Studies have shown that as the mass fraction of CS(wt.%)increases,the pore size of the large pores on the reverse side of the membrane gradually decreases,and the number of small pores gradually increases.Antifouling experiments showed that adding CS could alleviate the fouling of BSA.The highest average rejection ratio as well as flux recovery ratio(FRR_B)are80.4%(M-0.5)and 73.9%(M-0.3).The addition of CS reduces the degree of membrane fouling and the smallest irreversible fouling(R_ir)is 41.5%.The ordinary PVDF-CS membrane preparation method provides a potential solution to the low flux and fouling problems of ordinary PVDF microfiltration membranes.Finally,PVDF as raw material,PEG600 as hydrophilic modifier,PVPK30 as porogen,DMAc as good solvent to prepare single and porous hollow fiber membrane.The inner as well as outer diameters of hollow fiber membrane were calculated by high power LED magnifying glass,and the structure and element types of hollow fiber membrane were characterized via SEM and EDS.The results show that the inner diameter of the single hole is 0.7±0.03mm,as well as the outer diameter is 1.2±0.01mm.Porous inner diameter is 0.8±0.01mm,the outer diameter is 1.2±0.02mm;The inner surface of a single pore is relatively smooth and the outer surface shows some white spots compared to the porous surface.From the SEM figure of cross section,it is easy to see that the single-pore and porous hollow fiber membranes have asymmetric structure.There are short finger-like pores in the middle of the cross section,and a dense layer of cortex is formed on both the inner and outer surfaces.It is because of this specific structure that the retention ratio is improved while the flux is guaranteed.The experimental results exhibit that the average flux of porous hollow fiber membrane is 258.1 L·m²·h^-1,which is significantly higher than the single-hole flux of 123.3 L·m²·h^-1,and the BSA rejection ratio of both can reach more than 80.0%.The application results of hollow fiber membrane show that it has a good removal effect on turbidity in water,and the removal ratio of turbidity in raw water can reach 98.0%.Further study showed that the hollow fiber membrane has good resistance to acid and base.With the increase of concentration in the soaking solution,the membrane flux was increased,as well as the rejection ratio of BSA decreased slightly.