Preparation of High Flux Chlorinated Polyvinyl Chloride Composite Ultrafiltration Membranes with Ternary Amphiphilic Copolymers as Anchor Pore-Forming Agents and Enhanced Anti-Fouling Behavior

N-Phenylmaleimide-styrene-maleic anhydride (NSM) copolymer, an inexpensive and commercial heat-resistant agent, was used as an additive in this work to tune the properties of chlorinated polyvinyl chloride (CPVC) composite ultrafiltration membranes. The NSM chains did not agglomerate in the casting solution, but increased the thermal instability, leading to faster phase separation and changing the cracked pores to rounded pores on the membrane surface. Moreover, the cross-section appeared with sub-layered finger-like macropores and micropores, which facilitated the rapid passage of water through the membrane. Notably, NSM copolymers were anchored to the membrane surface and the cyclic groups (maleic anhydride and maleamide) were not hydrolyzed during the phase separation as demonstrated by ATR-FTIR and XPS analysis. This may affect the membrane separation behavior. The results indicated that the pure water permeability of NSM-tuned membranes increasing by 350% that of pristine membrane. The rejection of all NSM-tuned membranes was higher than 90% for humic acid (HA) and 85% for sodium alginate (SA), which still outperformed the pristine membrane. With a NSM content of 5 or 10 wt % for two foulants (20 mg/L SA and 100 mg/L HA), the FRR of the NSM-tuned membrane exceeded 90.0% and the reversible flux decline ratio reached 50%, exhibiting better anti-fouling performance. Extended Derjaguin-Landau-Verwey-Overbeek theoretical model was utilized to evaluate and analyze the fouling mechanisms of the NSM-tuned membrane. Therefore, NSM can not only play a role of pore-forming but also significantly enhance the separation behavior of the CPVC membrane, providing a reference for future environmentally friendly membrane manufacturing processes.

Automated summary

In this study, N-Phenylmaleimide-styrene-maleic anhydride (NSM) copolymer was used as an additive to modify the properties of chlorinated polyvinyl chloride (CPVC) composite ultrafiltration membranes. The addition of NSM changed the morphology of the membrane surface and improved its thermal stability and water permeability. The NSM copolymers remained anchored to the membrane surface during phase separation, which affected the membrane separation behavior. Moreover, the NSM-treated membranes exhibited higher rejection rates for humic acid and sodium alginate, showing better anti-fouling performance.