Hydrophilic Modification Of PTFE Flat Sheet Membrane

With the development of membrane separation technology, more and more membranematerials are used in environmental protection, water treatment and other fields.Polytetrafluoroethylene (PTFE) flat sheet membrane is regarded as the ideal filter materialbecause of its acid and alkali resistance, chemical corrosion resistance and the advantages ofhigh porosity, high flux and so on. So PTFE flat sheet membrane can adapt to the harshenvironment in the field of water treatment. But due to the strong hydrophobic in the surface ofPTFE flat sheet membrane and the surface wettability is poor, which limited its appilication inthe field of water treatment. So the hydrophilic modification of PTFE flat sheet membrane hasbecome a hot topic of researchers at home and abroad.Based on the understanding of that traditional chemical modification of PTFE flat sheetmembrane can damage body structure. A physical hydrophilic modification method wasinvestigated in this study. It took hydrophilic material as vine and the fibril in the PTFE flat sheetmembrane as tree. Using adhesive firmly attached the hydrophilic substances to the membranesurface by chemical crosslinking. The structure and hydrophilic of the surface of PTFE flat sheetmembrane before and after the hydrophilic modification was investigated by Scanning ElectronMicroscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and contact angle. It alsotested the filtration performance and resistance to protein polluting of modified PTFE flat sheetmembrane. The main contents and achievements of the thesis are as follows:(1) Using the solution of poly(butyl acrylate)(PBA) and ethanol to infiltrate the membraneand the hydrolysis reaction accurred on the membrane surface under the catalytic action ofNaOH. The experimental results show that the surface of modified membrane remainsfibrillar-node network strcuture, part of the fibrils become slim, nodes become large, andseveral solid matter accurred on part of the nodes, the microporous increases from the originalfilm and porosity is a bit down; It also show that the hydrophilic group of-OH and-COOHadhered to the surface of modified membrane, contact angle dropped from137.1°to76.8°andthe initial water flux was1043.9kg·m-2·h-1. The hydrophilic persistence of the modified PTFEflat sheet membrane is good, the rejection of turbidity of crystal grinding wastewater was99.88%, and the modification effectively inhibited the pollution of protein adsorption. Theoptimum conditions of experiments: the concentration of PBA alcohol solution is30g·L-1, theconcentration of NaOH solution is0.3M, the hydrolysis temperature is70℃and the hydrolysistime is2h. (2) The PTFE flat sheet membrane was hydrophilic modified by using polystyrene sulfonate(PSS) as a hydrophilic agent, polyvinyl alcohol (PVA) as an adhesive and glutaraldehyde (GA)as a crosslinking agent. The experimental results show that original PTFE flat sheet membranehas fibrillar-node spider mesh structure, uniform distribution of pore size and high porosity.Afterthe hydrophilic modification, the membrane surface remains fibrillar-node structure, part of thenodes become large, the fibrils become thick and the average pore size becomes smaller than theoriginal film and the membrane porosity decreases. It also show that the hydrophilic group of-OH and-SO3Na adhered to the surface of modified membrane, contact angle dropped from137.1°to66.1°and initial water flux was963.9kg·m-2·h-1. The hydrophilic persistence of themodified PTFE flat sheet membrane is good, the rejection of turbidity of crystal grindingwastewater was99.88%, and the modification improved the resistance to protein polluting. Theoptimum conditions of experiments: the concentration of PVA is30g·L-1, the concentration ofGA is35.7g·L-1and the concentration of PSS is26g·L-1. Dipping PTFE membrane to the mixedsolution of reagent above and baking it under70℃.(3) The PTFE flat sheet membrane was hydrophilic modified by esterification crosslinkingreaction between polyacrylic acid (PAA) and PVA. The experimental results show that modifiedPTFE membrane remains fibrillar-node mesh structure, several nodes mergers, fibrils becomethick and part of the microporous increase from the original film, but the membrane porositydecreases. It also show that the hydrophilic group of-COOH,-OH and C=O adhered to thesurface of modified membrane, contact angle dropped from137.1°to65.3°and initial water fluxwas158.9kg·m-2·h-1. The hydrophilic persistence of the modified PTFE flat sheet membrane isgood, the modification improved the resistance to protein polluting. The optimum conditions ofexperiments: the mass ratio of PAA and PVA is3/1, adding a small amount of mixedcrosslinking agent, the esterification temperature is100℃.