Study On Hydrophilic Modification Of PTFE Microporous Membrane Based On Hydrogel Coatintg Method

At present,water pollution and water shortages problems have seriously threatened people’s lives.For a long time,the treatment of water pollution has always been the focus of environmental protection scholars.Membrane technology has become one of the mainstream management methods because of its green environmental sustainability and rapid and efficient separation process effects.PTFE microporous membrane materials have been attracting the attention and research of international scholars because of their excellent chemical resistance,high porosity and good mechanical properties.However,due to its low surface energy and high hydrophobicity,PTFE microporous membranes greatly limit its application in water treatment.Therefore,improving the hydrophilic properties of PTFE microporous membranes has become the focus of research.In this paper,polyvinyl alcohol（PVA）and chitosan/oxycarboxymethyl chitosan is used as a hydrophilic agent,and a cross-linking reaction is used to coat a layer of hydrogel on PTFE microporous membrane fibers by different crosslinking agents to achieve hydrophilic modification of the PTFE microporous membrane.Specifically carried out the following two parts of research:（1）Selecting hydrophilic polyvinyl alcohol（PVA）and chitosan（CS）with good antibacterial properties as the material,under the alkaline condition,the hydrogel coating is formed by the cross-linking of epichlorohydrin,combined with in-situ embedding of SiO₂ nanoparticles for the modification of PTFE microporous membrane.The experimental results showed that the surface of the fiber of the modified PTFE microporous membrane is covered with a layer of hydrogel and a large amount of solid particles are attached to the hydrogel coating and resulting in improved surface roughness,and the average pore diameter and porosity are slightly reduced.Hydroxyl and amino groups appear on the surface of the hydrophilic modified PTFE microporous membrane;new elements N,O,Si appear on the surface of the hydrophilic modified PTFE microporous membrane.With the increase in concentration of the PVA solution,the water flux of the modified membrane first increases and then decreases.In addition,the contact angle of the membrane surface first decreases and then stabilizes.With the increase of reaction time,the water flux of the modified membrane increases first and then decreases.With the increase of reaction temperature,the water flux of the modified membrane first increases and then decreases,also the contact angle of the membrane surface first decreases and then rises.The optimal reaction conditions are found to be with:PVA solution concentration of 1wt%,CS solution concentration of 0.3wt%,and the mass ratio of CS solution to PVA solution is 1:1.5,the reaction time was 6h,the reaction temperature was 40°C,the reaction pH was 12,and the water dilution ratio in the secondary treatment was 45 times（in which PBA:SiO₂=1:2.5）.The contact angle of the hydrophilic modified PTFE microporous membrane was reduced from 136°to 48°,and the pure water flux reached 3172L·m^-2·h^-1.The results of oil-in-water emulsion separation experiments on hydrophilic modified PTFE microporous membranes showed that the hydrophilic modified PTFE microporous membrane has good oil resistance and oil retention（97%）.The physical and chemical stability of the hydrophilic modified PTFE microporous membrane showed that the hydrophilic modified PTFE microporous membrane has good acid resistance and washing resistance.（2）The PTFE microporous membrane was modified by cross-linking reaction between polyvinyl alcohol（PVA）and oxycarboxymethyl chitosan（OCMCS）under neutral conditions to impart hydrophilic properties with glutaraldehyde.The results showed that the surface of the fiber of PTFE microporous membrane is covered with a layer of hydrogel coating,and the surface of the microporous membrane remains the original three-dimensional network structure;the hydrophilic modified PTFE microporous membrane surface has a hydrophilic base with the presence of hydroxyl groups and amino groups.As the PVA content in the reaction solution increases,the water flux of the modified membrane increases first and then decreases,and the contact angle decreases first and then increases.As the reaction temperature increases,the modified membrane water flux increases first increase and then decrease,the contact angle decreases first and then increases;as the reaction time increases,the water flux of the modified membrane first increases and then decreases,and the contact angle decreases first and then increases.The optimum experimental conditions were:OCMCS/PVA mass ratio was 1:1,glutaraldehyde（5wt%）and hydrochloric acid solutions（1wt%）were 2.5mL and 1mL,respectively,and the reaction time was 6h and at the temperature of 50°C.The prepared PTFE-PVA/OCMCS membrane had a greater water flux of 4480.89L·m^-2·h^-1 and a contact angle of 57.48°.The anti-pollution performance test results of the hydrophilic modified PTFE microporous membrane showed that the PTFE-PVA/OCMCS membrane had good anti-bovine serum albumin（BSA）adsorption capacity.The results of long-time washing experiments show that the PTFE-PVA/OCMCS membrane has good physical stability.