Study On The Performance Of PVDF Membrane Modified By Nanoparticles To Retard Membrane Aging

More and more attention has been paid to the stability of ultrafiltration membrane materials in the process of membrane drinking water treatment.PVDF(polyvinylidene fluoride)is a widely used membrane material,in order to improve the removal effect of pollutants,it is inevitable to use strong oxidizing agents for chemical cleaning.The chemical agents will decompose to form free radicals with small polarity and strong activity,which will rapidly spread into the polymer to trigger the aging process,and eventually lead to the degradation and performance degradation of membrane materials.Therefore,it is of great significance to slow down the oxidation of organic membrane materials by free radicals for the safe and stable operation of membrane drinking water process.To solve these problems,a new method for the determination of free radicals in sodium hypochlorite solution by electron spin resonance and salicylic acid spectrophotometry was proposed.The experiment results show that the free radical scavenging rate of 0.5wt%nano-titanium dioxide(nano-TiO₂)or carboxy-modified multi-walled carbon nanotubes(MWCNT_S-COOH)can reach more than 86%,which proves the oxidation resistance of nanoparticles and analyzes the mechanism of free radical scavenging of nanoparticles.When p H=9,the free radical activity was strong,and the subsequent accelerated aging experiments were carried out under this condition.The PVDF modified membranes PVDF-PVP/TiO₂ and PVDF-PVP/CNT were prepared by blending modification method,as well as the original PVDF-PVP without nanoparticles.The membrane materials were further immersed in 2000 ppm(p H=9)sodium hypochlorite solution for 30 days for accelerated aging experiment.Through the surface chemical properties(FTIR,XPS),surface morphology(SEM),surface hydrophilicity(contact Angle),surface electronegativity(Zeta potential)and mechanical properties(tensile fracture strength)to explore.Compared with PVDF-PVP after aging,PVDF-PVP/TiO₂ and PVDF-PVP/CNT can effectively inhibit the formation of macropores after aging treatment,the pure water flux increased by 43.1%and 70.6%,and the tensile strength was increased by 46.3%and 59.2%.FTIR showed that the degradation(crosslinking and precipitation)of PVP(polyvinylpyrrolidone)hydrophilic additive was effectively inhibited,the aging rate was reduced,and the chemical stability of the membrane material was improved.This study proposed a new conclusion that the nano-particle blend could effectively improve the antioxidant property of PVDF membrane itself.The experiment further explored the influence of different dosage of nanoparticles(0.25wt%,0.5wt%,1wt%)on the oxidation resistance of the membrane,and it was found that 1wt%nano-TiO₂ modified membrane had stronger anti-aging performance,while 0.5wt%MWCNTS-COOH maintained good anti-aging performance.This is because the carboxyl-modified MWCNTs have more holes and higher contact rate with free radicals,so the effect of carbon nanotubes is better than that of titanium dioxide.Free radicals preferentially react with the contact sites on the nanoparticles to form macromolecular free radicals and water,which reduces the attack of free radicals on membrane matrix PVDF and additive PVP,the addition of nanoparticles with free radical scavenging function significantly slows down the aging.This paper analyzed the reason and mechanism of anti-aging of nano-particle modified membrane,which provided theoretical support for reducing the process cost and extending the service life of membrane.