Electro Kinetic Behavior On The Surface Of PVDF Hollow Fiber Membrane Modified By Low-Temperature Plasma Method

Polyvinylidene fluoride (PVDF) material has some character such as excellent chemistry stability, radiation resistance, heat resistance and good mechanical intensity, and it has been widely used in some field of water treatment, chemical industry, biology and medicine, etc. When PVDF was used in micro filtration and ultrafiltration as one of main membrane material, membrane pollution became the main factor which effects the separation efficiency due to its low surface energy and high hydrophobic. So its application was limited in the separation system. Low-temperature plasma treatment is one of the effective methods to solve the problem. This paper researched the modification condition of PVDF hollow fiber membrane plasma modification by the plasma treatment, plasma initiated polymerization and plasma polymerization, and some reasonable modification parameters was obtained. By designing flow potential measurement device, membrane hole and membrane surface charged performance strength of modification PVDF hollow fiber membrane was described, and the electrokinetic behavior on the surface of modification PVDF membrane was also investigated. This paper also researched the water flux with modification membrane, and using attapulgite colloid solution as filtering prefiltration, the rules of change was researched the variation of flux and flow potential with time during the process of membrane pollution. The experimental results were as follows:(1) Using Changzhou big plasma research & development Co., ltd., manufacturing plasma processing equipment for PVDF hollow fiber membrane plasma modification, Ar for plasma gas, the process parameters were that:①AA coating graft polymerization:PVDF membrane soaked in 50% of acrylic acid solution for 3 min, glow discharge time for 2 min and power for 60 W; AM coating graft polymerization:PVDF membrane soaked in 10% of AM solution for 10min, glow discharge time for 3 min and power for 70 W.②Plasma surface treatment technique:glow discharge ime for 10 min and power for 130 W.③Plasma trigger radical grafted:glow discharge time for 3 min and power for 210 W, then introduced AA monomer grafting for 30 min.④plasma deposition polymerization by AA: plasma surface treatment for 30 s and glow discharge power for 50W, then introduced AA and glow discharge for 90 s, power for 25 W.(2) Using self-made flow potential measuring device, the hollow fiber membrane surface flow potential and membrane pore flow potential were determined for 0.001mol/L of KCl solution as background electrolyte solution. As the differential pressure on both ends of membrane is bigger, the absolute value of flow potential is greater. According to flow potential and pressure of the slope calculate Zeta potential. The results showed that the Zeta potential of membrane modified by AA/AM coating graft polymerization, plasma deposition polymerization by AA, plasma trigger radical grafted, plasma surface treatment technique is-4.15 mV,-3.3 mV,-3.19 mV,-2.66 mV,-1.87 mV respectively.(3) Flux tests of modification membrane showed that flux recovery rate of membrane modified by AA/AM coating graft polymerization,plasma deposition polymerization by AA,plasma trigger radical grafted,plasma surface treatment technique was 9.9%,38.3%,72.3%, 28.2%,68.5% respectively. The range of flux recovery rate at different pH value was 15.9%, 22.7%,9%,6.7%,7.6% and the results showed that the flux had increased with the decreasing of pH value. The results of starting bubble point pressure test showed the pore size of AA/AM coating graft polymerization modification membrane have no change. But the pore diameter of plasma deposition polymerization by AA, plasma trigger radical grafted, plasma surface treatment technique modification membrane becomes larger.(4) With attapulgite colloid solution as the filtering prefiltration, modified PVDF hollow fiber membrane's separation properties and resistance pollution performance had been tested. The results showed that the modified membrane flux depression was lower, and the flow potential value was higher with the membrane modified by AA/AM, however, the modified membrane flux depression was higher, and the flow potential value was lower with the membrane modified by plasma surface treatment.