Polyacrylonitrile Modified By Copolymerization With Poly(Ethylene Glycol) And The Separation Performance Of Its Microporous Membrane

Polyacrylonitrile-poly(ethylene glycol)-polyacrylonitrile (PAN-PEG-PAN) block copolymers without polyacrylonitrile have been synthesized by the redox method with ceric ion-alcohol(PEG) system, and their micro-porous membranes were prepared bythe phase inversion.The polymerization conditions were established through a lot of experiments. The structure and chemical composition of the block copolymer were characterized by Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared (FTIR) spectroscopy, Element Analysis (EA) and Differential Scanning Calorimetry (DSC). Also, the influences of the molecular weight and concentration of PEG, concentration of AN monomer, and polymerization temperature on the intrinsic viscosity of the block copolymer were studied in detail. The studies shows that among the polymerization conditions for preparing amphiphilic block copolymer of polyacrylonitrile-poly (ethylene glycol)- polyacrylonitrile without polyacrylonitrile homopolymer containing the polymerization temperature, concentrations of certain Ce(IV) salts , AN monomer concentration and the polymerization time, the intrinsic viscosity (molecular weight) of the block copolymer increases with rising polymerization temperature (-1 ℃ ≦ T≦10℃), or decreasing the molecular weight and concentration of PEG, and decreasing the concentration of the Ce(IV) salts in polymerization. And the AN segment weight fraction (Wan) in PAN-PEG-PAN block copolymers increases with decreasing the molecular weight of PEG used in polymerization.PAN-PEG-PAN microporous membranes were prepared by the phase inversion. Both water flux and porosity of the membrane increase firstly, and then decrease with increasing the PEG content(W_EG) in the membrane, the maximum values are 965.6 L m^-2 h¹ and 83.0% respectively as the W_eg is 0.096, and the pore size of the membrane increases at first, and then decreases with increasing W_eg. When NaNO₃ used as additive was added in the casting solvent, the pore size of PAN-PEG-PAN membrane became larger as the content of NaNO₃ increased. The pore size of the membrane became small with increasing the polymer content, and both water flux and porosity of the membrane decreased with increasing the polymer content. The pore size of the membrane became larger with increasing the temperature of coagulationbath, and both water flux and porosity of the membrane increased with increasing the temperature of coagulation bath. When using K2SO4 as coagulation bath, the pore size of the membrane became small with increasing the content of K2SO4 in the coagulation bath, and both water flux and porosity of the membrane decreased with increasing the content of K2SO4.PAN-PEG-PAN membranes treat wastewater effectively. It was found that it could remove the particles larger than 100 nm and raise the light transmission of the ink model wastewater from 32.1% to 98.7%. When the membranes were used for treating the dyeing wastewater, the light transmission of filtrate increase with increasing the Weg, and the resistance to pollution of the microporous membrane is much better than the PAN microporous membrane. It attributed to the hydrophilicity, porosity of the PAN-PEG-PAN membrane and the morphology of inner cross-sections.