Study On The Evolution Of Microstructure And Performance Of Polyhydroxy Polymer Grafted Ultrafiltration Membrane

Hydrophobicity of Poly?vinylidene fluoride??PVDF?makes it is easy to be fouled and the service life of membrane is shorten,and the development of PVDF in the water treatment industry is hindered.At present,it is generally believed that the reason why hydrophilicity modification can improve the anti-fouling capacity is that the bonded water layer which can play a physical and energy protection role is formed between hydrophilic groups and water molecules through hydrogen bond,which can effectively prevent pollutants to touch the membrane surface,so as to improve the anti-fouling capacity of the membrane.However,there are only theoretical discussions and no detailed quantitative analysis in related research.The physical blending and chemical grafting modification are combined,and the work is carried out mainly from four aspects in this paper.Firstly,glycerol triacetate?GTA?was used as diluent to prepare PVDF/SMA membrane by thermally induced phase separation technology?TIPS?.The effects of the SMA model,the PVDF/SMA proportion and the additive type and dosage on the membrane structure and properties were investigated to determine the process parameters of the PVDF/SMA blending membrane.The membrane structure is through,the flux is moderate and the rejection is high when the SMA model is S3,the PVDF/SMA proportion is 8/2 and the 2%PVP-K30 is added.Secondly,the PVDF/SMA-g-PEG grafting membrane was obtained by the esterification between hydroxyl group of PEG and acid anhydride of SMA on the membrane.The position of the PEG with different molecular weight was investigated,the thickness and tightness of BWL were quantified,and the mechanism and factors of membrane permeability were analysed.The results showed that the PEG chains are grafted on the upper and the matrix near the upper surface of membrane when the molecular weight of PEG is smaller than 2000 g mol^-1,on the contrary,they are grafted on the upper surface of the membrane.The BWL was formed by hydrogen bond between the hydroxyl groups and ether bonds of PEG and water molecules,the thickness and tightness of BWL reached the maximum when the M_w was 2000 g mol^-1.In addition,the tightness of the BWL increase the rejection and anti-fouling capacity of the membrane,and filtration resistance has a great influence on flux.Thirdly,the main influencing factor and optimal reaction conditions were determined by combining the single factor experiment and the response surface method under the condition of PEG molecular weight was 2000 g mol^-1.Research indicated that the effect of reaction temperature was maximum and the highest GD was obtained when the values of reaction time,catalyst dosage and reaction temperature were 4.12 h,0.6%and 73.19?,respectively.Activation energyFT-IR.In addition,the structure,performances and resistances of the membrane were characterized and analyzed.The hydrophilicity of grafting membranes has been improved,the surface charge turned to 0,and the total permeation resistance was decreased with the increase of GD.Finally,the PVDF/SMA-g-PEG-g-PVA was prepared by intermolecular crosslinking of glutaraldehyde?GA?,which was crosslinker,with the hydroxyl groups of PEG and polyvinyl alcohol?PVA?.The thick and tight BWL helps to improve the rejection of membrane.In addition,the hydrophilicity of membrane was obviously improved and the contact angle in 30 s was 34.7°when the concentration of PVA was8%,which meant the hydrophilicity was best.