Study On Preparation And Properties Of Positively Charged Nanofiltration Membrane With Hyperbranched Structure

Owing to its unique structure, hyperbranched polymers have attracted more and more researchers. However, there have been little reports about the utilization of hyperbranched polymers as membrane material until now. No reports have been found on using the layer-by-layer (LBL) self-assembly method to prepare hyperbranched nanofiltration membrane. Aimed at increasing the flux of the nanofiltration membrane, a novel hyperbranched cationic poly-(2-(acryloyloxy)ethyl)trimethylammonium chloride was designed and synthesized in this study. Then, the composite nanofiltration membrane with excellent separation performance was prepared by the LBL self-assembly method and was subsequently applied to separate the crystal violet dye.Firstly, the semicontinuous reversible addition-fragmentation chain transfer (RAFT) method was employed to synthesize the macro chain transfer agents b-PAM and the polymerized product b-PDAC. Then, FTIR, NMR and MALLSGC were then used to characterize the structure, molecular weight and molecular weight distribution of the polymer. The results showed that the hyperbranched cationic polymer b-PDAC was most suitable to prepare the nanofiltration membrane when the preparation condition was [AM]/[DAC]=4:5, [AM]/[BCPA]/[APS]=600/1/0.5, [MBA]/[CTA]=20, the feeding time of MBA 2h and the time of chain extension 4h. The weight-average molecular weight of the polymer was 1.828 X 106, while the dispersion index and the branching coefficient were 1.959 and 0.664, respectively.Finally, LBL self-assembly method was employed to prepare hyperbranched nanofiltration membrane with poly(styrene sulfonic acid) sodium salt (PSS) and b-PDAC as the anionic polyelectrolyte and cationic polyelectrolyte, respectively. The hyperbranched nanofiltration membrane prepared was then studied from the view of ATR-IR, SEM, AFM, CA and separation performance. The results showed that when the concentrations of b-PDAC and PSS were both 25g·L-1 and the number of the layer was 2.5, the surface roughness of the [b-PDAC25/PSS25]2/b-PDAC composite nanofiltration membrane was 12.2nm, which was a little higher than the commercial DL membrane. Although the rejection rate of 0.5mg·L-1 Crystal violet of the [b-PDAC25/PSS25]2/b-PDAC composite nanofiltration membrane was 94.23%, which was slightly lower than that of the NF 270 membrane, but its flux was 1.5 times higher than the NF270 membrane. Thus, compared with the traditional membrane, the nanofiltration membrane with hyperbranched structure had increased the membrane flux markedly with only little loss of the rejection rate.