| In recent years,with the rapid development of the economy and the continuous improvement of the living standards of urban and rural residents,people's demand for clean water resources is also growing.However,due to frequent water pollution and other phenomena,China is facing increasing pressure on freshwater supply.With the advantages of high separation efficiency,low energy consumption and good treatment effect,membrane separation technology has been fully applied in the field of sewage treatment.Polytetrafluoroethylene(PTFE)hollow fiber membranes are commonly used as microfiltration membranes,which have strong chemical stability and occupy an important position in separation membranes.And because of its low surface energy and poor wettability,PTFE has low flux and easy to be polluted.Moreover,the preparation of PTFE hollow fiber membranes in China started late and the process needs to be improved.All these problems restrict the development of PTFE hollow fiber membranes.Therefore,this paper optimizes the preparation process of PTFE hollow fiber membranes,and uses the oxidative self-polymerization of dopamine to improve the surface wettability of the membranes,thereby improving the water flux.(1)Exploring the improvement of mixing process.An automatic mixer with fuel injection system was designed.The mixing mode of PTFE resin and lubricant was changed from traditional oil pouring mixing to oil injection mixing to obtain more uniform PTFE paste.(2)The determination of dopamine self-assembly modification scheme.Aiming at the hydrophobicity of the surface of the PTFE membrane,the self-assembly of dopamine was used to deposit polydopamine coating on the surface of PTFE film to improve the surface wettability.The surface morphology and chemical composition of the modified film were analyzed to determine the successful deposition of polydopamine coating on the membrane surface.By testing the static water contact angle of the membrane surface before and after modification,the feasibility of the dopamine self-assembly modified PTFE scheme was proved,and the contact angle was successfully reduced from 137 to 81°,which effectively improved the hydrophilicity of the membrane.The reaction conditions were as follows: the concentration of dopamine solution was 0.1 mol/L,the pH of the reaction system was 8.5,and the reaction time was 12 hours.(3)Dopamine-induced modification of PTFE hollow fiber membranes by oxidants.The above reaction was optimized using copper sulphate/hydrogen peroxide and ammonium persulfate,respectively,to increase the reaction rate.The experimental results show that the oxidant induction can greatly increase the oxidation rate of dopamine,in which the reaction rate induced by copper sulfate/hydrogen peroxide is higher than that of ammonium persulfate;the modified film induced by copper sulfate/hydrogen peroxide reaches the dopamine immersion time.At 1 h,the contact angle reached 85° and then stabilized.When the ammonium persulfate-induced dopamine was modified for 2 h,the contact angle dropped to 60°.The comprehensive reaction time and modification effect,the final determination of dopamine-modified PTFE membrane in this project is: dopamine solution concentration 0.1 mol/L,ammonium persulfate concentration 0.05 mol/L,reaction system pH 8.5,reaction time 2 h.(4)PTFE hollow fiber membrane filtration application exploration.The water flux,particle interception and filtration efficiency and coating stability of the modified membrane were measured,and the feasibility of the modified scheme was verified.The modified PTFE membrane has improved hydrophilicity and increased flux,which can effectively intercept particles of 5 ?m and above,and the single filtration efficiency is over 98%;it can adapt to various solution environments and keep the coating stable.The flux can be restored by ultrasonic cleaning after blocking the membranes.Modified membranes obtained by this way have important ecological and economic values in the field of filtration. |
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