Basic Studies And Application Of Modified Polymer Membranes By Low-Temperature Plasma

Low-temperature plasma technique has been developed to modify the surfaces ofpolymer membranes. It could endow the polymer membrane surface many excellentproperties without changing its bulk properties. The physical or chemical changeswhich could not be realized by normal reactions could be initiated quickly andefficiently by plasma technique. So low-temperature plasma technique has beenextensively used to modify the polymer membranes.This dissertation concerns using the low-temperature plasma toprefunctionalize poly-acrylonitrile(PAN) and polyvinylidenefluoride(PVDF)ultrafiltration membranes in vapor or liquid phase, and then the monomerswith different properties were introduced to the surface pores of themembranes. Therefore, the surface pore size and its distribution of themembranes can be adjusted from ultrafiltration to nanofiltration by the reationconditions.Styrene, the hydrophobic monomer, was grafted onto the surface of PANmembranes by the low-temperature plasma in gas phase, whileN-vinylpyrrolidone (NVP), the hydrophilic monomer, was grafted onto themembrane surface in aqueous phase. The surface structure of the modifiedmembranes were determined by FTIR-ATR and XPS, while the pore size ofthe membrane before and afer grafting were measued by DSC technique. Theeffect of operation condition, such as plasma power, plasma treatment time,grafting reaction time, on the separation properties and water flux of themembranes were investigated. The styrene grafted PAN membrane using lowtemperature plasma technique showed excellent chemical resistance andrejection for the separation of toluene and ketone from lube oil. For the feedcomposition of 83.94wt% solvent, the solvent in permeate solution was98.42wt%, and the rejection of lube oil was 90.2%. Furthermore, the flux andrejection of NVP graft PAN membranes were invesigated by the separation ofmixed salt (MgSO4+NaCl)/water system. The NVP grafted PAN membranesexhibited applicable separation performances for mixed salt(MgSO4+NaCl)/water system. At 2 MPa, the rejection of mixed salt by using the modifiedmembrane reached 83.54%.Moreover, PVDF ultrafiltration membrane surface was modified by lowtemperature plasma technique, so that the surface pore size of the membranedcan be adjusted by the reaction condition. By argon (Ar) treating andsubsequent grafting reaction, styrene, a hydrophobic monomer, wasintroduced onto PVDF membrane surface. The structure and chemicalcomposition of the PVDF membrane surface were characterized by ATR-FTIR.The surface morphology of PVDF membrane were observed by scanningelectron microscope (SEM), and atomic force microscopy (AFM). The poresize and its distribution of the membrane surface was determined bydifferential scanning calorimeter (DSC). The varation of the pore size and itsdistribution and the water permeability with grafting reaction condition, suchas plasma treatment time, the graftiong time, and the grafting temperaturewere investigated. The results showed that styrene monomer was successfullygrafted onto PVDF membrane surface. With the increasing in plasma time andgraft time, the pore size of modified membranes decreased and thedistribution of pore size narrowed, and the pure water flux decreased.