Preparation of the interfacial enhanced PA/APVC nanofiltration membrane based on the in-situ amination of substrate membrane

Abstract

In this research, a novel interfacial enhanced thin film composite nanofiltration (TFC NF) membrane with nail-fixed like surface structure and wave line like cross-section structure, good permeability and superior interfacial stability was prepared by interfacial polymerization (IP) on one-step in-situ aminated polyvinyl chloride (APVC) support layer. The effects of amination agent (triethylenetetramine, TETA) content on the support layers and the effects of the support layers with different degrees of amination on the performance of the TFC NF membranes were studied comprehensively. Furthermore, the interfacial bonding strength of the TFC NF membrane was explored by the inverse permeation test. It was concluded from the results that higher TETA content in casting solution led to the APVC membrane to form macroporous surface structure, thinner top skin layer and larger mean pore size. Meanwhile, more TETA molecules were grafted onto the PVC chains through nucleophilic substitution to participate in IP in a synergistic manner. Accordingly, the corresponding TFC NF membrane formed a nail-fixed like surface structure similar to semi-free-standing polyamide (PA) layer and wave line like cross-section structure with thinner and denser active layer. The water flux of the TFC NF membrane prepared with the optimized APVC membrane as the substrate membrane was increased by 395% at 0.6 MPa compared with the TFC NF membrane prepared with PVC membrane as the substrate membrane, while Na2SO4 rejection did not sacrifice and increased by 3.48%, which manifested that unique structure was favorable to speed up the water transmission and effectively conquered the trade-off effect. Moreover, the representative TFC NF membrane prepared with optimized APVC membrane as the substrate membrane with strong covalent bond between support layer and active layer demonstrated superior interfacial stability in the short-term circulating inverse permeation test.