Study On The Preparation Of Novel Polymeric Membrane By Surface Grafting Modification

Water treatment becoming an important subject attracted attention of scienctists from domestic and international academia as the problems in water resource and environmental pollution are getting worse.Among those water treatment processes, the membrane methods have obvious advantages as no additives are used, small energy consumption, high yield, and easy to recycle. The application of membrane methods are dominated by the application of polymer membranes. As he application of the membrane is a direct result of the membrane property, preparation of suitable membranes is an extremely important work.However, membranes composed of single component can hardly be a combination of well filmed, long stability, powerful functionality and cost-efficiency. So, it is generally take use of physical and chemical methods to improve the performance of membranes to satisfy actual applications. Among those methods,surface grafting modification is simple, cost-efficient, stable and widely used.This paper focus on those problems that ordinary single electrospun nanofibrous materials are usually hydrophobic and lack of functional groups, and the separation layer is easily striped and even come off from the supporting layer as the low adhesive strength between them and it has complicated technics. We explore the construct of a novel hydrophilic, functionalized, structurally stabled and easily prepared polymer membrane. This paper includes three parts:1. Presented a method for a novel surface grafting modified hydrophilic polyvinylchloride(PVC) micro/nanofibrous membrane. This work firstly explored the technology of electrospinning for PV C micro/nanofibrous membrane, then grafted hydrophilic olefine monomers(e.g. N-vinyl pyrrolidon e(NVP), dimethylaminoethyl methacrylate(DMAEMA), acrylamide(AM)) onto the surface of PV C micro/nanofibrous membrane. The results showed that the water contact angle of PVC micro/nan ofibrous membrane decreased from 137 ± 0.5° to approximately 60°. Its hydrophilicity is improved and its mechanical properties can be well maintained at the same time. Thus, this method is help ful to solve the problems like larger pressure drop, lower flux and easier to be polluted arising fr om the application of hydrophobic PVC micro/nanofibrous membrane in the process of water treat ment.2. Developed a novel PVC@PDA-PEI membrane-shaped adsorbing material by polydopamine(PDA)assisted grafting method as well as a simple and versatile approach for the fabrication of a amino groups grafted nanofibrous membrane. This method take advantage of dopamine to form a firmly adhered coating on the surface of PVC nanofibrous membrane via spontaneously oxidative polymerization, which could not only improved the hydrophilicity of PVC nanofibrous membrane, but also provided an extremely versatile platform for secondary reactions for PEI grafting. Furthermore, Cu2+ was selected as the target pollutant to investigate their adsorption properties toward heavy metals. The results indicated that PEI-grafted membranes can adsorbed Cu2+ strongly by coordination and the absorption equilibrium data of were well fitted with the Langmuir adsorption isotherm with a maximum adsorption capacity value of 33.59 mg·g-1,which was two times of the fresh. The removal efficiency of Cu2+ merely reduced 4.7% for PVC@PDA-PEmembrane after 3 cycles of adsorption-desorption process. Further analysis of the mechanism showed PEI grafted to the polydopamine coating via Michael addition does not harm to the catechol structure; rather,PEI grafting provided quantities of amino groups which can binding Cu2+. Thus the adsorption capacity of modified membrane for Cu2+ improved greatly. This study provides a very good reference to the preparation of amino groups modified nanofibrous and this method settled the problem of amino groups can hardly grafted onto the surface of PVC-like nanofibrous membrane due to the lack of reactive sites.3. Developed a new method for surface chemistry, topology and performance controlled positive charged membrane via PDA assisted grafting modificaion. The surface hydrophilicity, charge properties, topology and morphology, and separation performance can be well adjusted by altering the generation of polyamidoamine(PAMAM).With the increase of PAMAM generation(from G0 to G2), the zeta potential of the PAMAM grafted membranes increased from 1.68 ± 0.69 m V to 4.88 ± 0.87 m V and the WCA changed from 52.2 ± 0.7o to 49.6 ± 0.4o, the Ra of membrane surface decreased from 8.85 nm to 3.87 nm.The SEM observation also shows that the PAMAM grafted layer firmly adhered to the PES substrate and a ralatively smooth surface was obtained after PAMAM G2 dendrimer grafting. Consequently, the PES/PDA-PAMAM membrane prepared by PAMAM G2 dendrimer has a higher rejections for multivalent cations(e.g. Mg Cl2 rejection is 93.15%) compared to that of the PES/PDA-PAMAM membrane prepared by PAMAM G0 dendrimer is much lower(83.67%). And the PES/PDA-PAMAM membrane possessed a good structural stability and anti-fouling properties suggested by the long-term testing. he polydopamine-assisted PAMAM grafting modification can serve as a facile, mild and controllable strategy to synthesize positive charged nanofiltration membranes and tailor it to meet the user’s actual requirements.