One-step Preparation Of Durable Hydrophilized PVDF-CTFE Membrane

Polyvinylidene fluoride(PVDF)is one of the most popular materials for the preparation of ultrafiltration/microfiltration membranes,and has been extensively studied and discussed.How to better resist membrane fouling during the use of PVDF membranes is a hot issue of recent research.Hydrophilic modification of membranes is considered to be a common and effective method for antifouling,and graft modification is an important means of hydrophilic modification.However,the PVDF segment contains high-energy C-F bonds,making the conditions for grafting reactions such as ATRP harsh and the grafting rate low.The polyvinylidene fluoridetrifluorochloroethylene(PVDF-CTFE)used in this paper can effectively avoid this problem.This copolymer pull CTFE segments in the PVDF segments,which provide low-bond and easily reactive C-Cl active sites while retaining the original excellent properties of PVDF.Based on the active site of C-Cl,a polyhydroxy hydrophilic substance N-methylglucamine(N-MG)which can react with it is used to hydrophilize the copolymer.In order to prepare a hydrophilic PVDF-CTFE membrane in one step,triethyl phosphate(TEP),which can dissolve PVDF-CTFE and N-MG at the same time,was selected as the solvent.In addition,TEP is less biotoxic,easily biodegradable,and recyclable than common organic amine solvents such as dimethylacetamide(DMAc)and dimethylformamide(DMF).In this paper,the solubility of N-MG in TEP was first tested,and then the effects of reaction conditions such as N-MG concentration,reaction temperature(casting solution temperature),and reaction time on membrane properties and structure were discussed.It proved by XPS,FTIR and other methods that the one-step modified membrane was successfully grafted with hydroxyl groups.Characterization methods such as contact angle test and water flux prove that the hydrophilicity of the modified membrane is significantly improved,and the mechanical property test proves that the one-step method has no great influence on the membrane strength.Based on this,the best modification conditions were selected by combining with the pore structure and other characterization methods: N-MG concentration of 2.5wt%,reaction temperature of 80°C and reaction time of 8 hours.Under these conditions,the water contact angle was reduced from 130 ° to 65.8 °,and the water flux was approximately doubled.In addition,based on the optimal conditions,this paper compares the difference between the one-step method and two common hydrophilization modification methods.One is to immerse the base membrane in N-MG solution,and use the amine radical in N-MG to react with the C-Cl active site in PVDF-CTFE to graft the hydroxyl on the surface of the membrane.The other one is to use N-MG to react with glutaraldehyde(GA)to increase the molecular segment so that hydrophilic substances are more easily adsorbed on the membrane surface or in the membrane pores.The experiment found that the one-step method used in this paper can complete the grafting reaction before membrane formation,which makes the hydroxyl groups exist in the entire membrane body.Therefore,under the premise of not having a great impact on the pore structure and mechanical properties,the effect of hydrophilic modification of PVDF-CTFE membrane by the one-step method is significantly higher than the other two modification methods.