Study On Polyphenol Tannins/Hydrophilic Polymer Modified Polyvinylidene Fluoride Membrane And Its Properties

The organic filter membranes have the advantages of low manufacture cost,high separation efficiency and low energy consumption,which are widely used in the field of water treatment.As a kind of organic membrane,Polyvinylidene fluoride?PVDF?membrane has more applications because of its high strength,high temperature resistance and chemical stability,but its hydrophobicity is so strong that it can be easily contaminated by protein and oil etc,thus to lose the filtration function,therefore,it's of great practical significance to improve the hydrophilicity and anti-pollution of PVDF membrane.In this study,polyphenol tannins and polyethyleneimine were used as hydrophilic modification materials for the surface hydrophilic modification of pristine PVDF microfiltration membrane,tannin and polyethyleneimine are both paintable and can react with each other to form crosslinking network,which can further enhance the force between the coating and PVDF microfiltration membrane.This study includes two aspects on the following:Firstly,the PVDF microfiltration membrane was coated by polyethyleneimine and 3-chloropropyltrimethoxysilane for the first step,which can form crosslinking on the membrane surface and is favorable for the coating of polyethyleneimine,and then coated by tannic acid for the second step to further improve the crosslinking and hydrophilicity.The influence of the ratio and dosage of modifiers,the modification time of each step,the pH value of tannin buffer and different modification process on the performance of modified membranes was investigated.The surface composition of modified membranes and reaction mechanism of the modifiers were characterized by attenuated total reflection Fourier transform infrared spectroscopy?ATR-FTIR?and X-ray photoelectron spectroscopy?XPS?,the surface morphology of modified membranes were observed by scanning electron microscope?SEM?,atomic force microscope?AFM?etc,the hydrophilicity,permeability,anti-fouling performance and stability of modified membranes were characterized by contact angle,pure water flux,flux recovery ratio,UV-vis absorption spectroscope?UV-vis?and the long-time rinsing tests.After modification,the hydrophilicity,permeability and anti-fouling performance of PVDF membranes are enhanced obviously,the stability of modified membranes is good in pure water and slightly inferior in strong acid and base.Based on the work above,the metal ions were introduced into the system by coordination with tannic acid and polyethyleneimine to further optimize the crosslinking network thus improve the performance of the modified membranes.And the influence of Zr⁴⁺,Fe³⁺,Al³⁺,Cu²⁺,Zn²⁺and Mn²⁺modification time on the performance of modified membranes was illustrated,the surface chemical composition of modified membranes was characterized by XPS,and the surface morphology of modified membranes was observed by field-emission scanning electron microscope?FESEM?,the contact angle,pure water flux,emulsion flux,flux recovery ratio and stability of the modified membranes were tested,in addition,the modified membrane rejection ratio for oil was characterized by UV-vis.Compared with the membranes modified by tannic acid and polyethyleneimine,the modified membranes in this aspect have better anti-fouling performance and stability,besides that,they also have better hydrophilicity than the pristine PVDF microfiltration membrane,demonstrating that the metal ions can change the structure of hydrophilic coating on the surface of PVDF microfiltration membrane and promote the membrane properties.