Development of polyacrylonitrile/polyacrylonitrile-g-poly(vinyl alcohol) hollow fiber ultrafiltration membranes with enhanced anti-fouling properties

Abstract

The objective of this study is to develop polyacrylonitrile (PAN)-based hollow fiber ultrafiltration (UF) membranes with improved anti-fouling properties for wastewater treatment. The prepared membranes were characterized with respect to their morphological structure, surface chemical composition, surface roughness, and hydrophilicity to investigate the impact of the membrane properties on the separation and anti-fouling performance. In the first stage of this study, PAN-based hollow fiber membranes incorporated with polyvinyl alcohol (PVA) were fabricated. Experimental results indicated that the resultant membranes demonstrated a trade-off between their separation and anti-fouling performances. Therefore, for the second stage, PAN-g-PVA graft copolymers of different properties (i.e. CP5, CP10 and CP15) were synthesized via ceric (Ce(IV))-initiated free radical polymerization by using different acrylonitrile (AN) monomer weights (5, 10, 15 g of AN per 10 g of PVA) and incorporated in the hollow fiber membranes. Obtained results revealed that the copolymer properties (i.e. number of PVA repeating units (nPVA)) significantly influenced the overall membrane properties. The highest pure water flux (179 L/m2.h.bar) was achieved by the membrane incorporated with graft copolymer of the highest nPVA of 70 due to the increase in hydrophilicity, pore size and porosity, and surface roughness. Thirdly, the investigation on the effect of the graft copolymer compositions in dope solution on the membrane properties and performances was carried out by using the best performance graft copolymer (CP10). The membrane properties and performance were significantly altered using the different copolymer composition. Membranes with the highest copolymer content demonstrated the highest water flux of 297 L/m2.h when tested at 1 bar which attributed to the changes in the membrane morphology, surface roughness and hydrophilicity. Overall, it was summarized that the UF performance and fouling property were mostly affected by the pore structure of the membrane and partly by the membranes physical properties (i.e. degree of PVA surface coverage and surface roughness) during filtration of bovine serum albumin (BSA), albumin from chicken egg white (EA) and trypsin. In the final stage, three different membranes; CP5 (incorporated with graft copolymer with nPVA of 68 at PAN:PAN-g-PVA weight ratio of 90:10), CP10-10 (incorporated with CP10 graft copolymer with nPVA of 25 at PAN:PAN-g- PVA weight ratio of 90:10) and CP10-5 (incorporated with CP10 graft copolymer with nPVA of 25 at PAN: PAN-g-PVA weight ratio of 95:5), which demonstrated among the highest flux recovery during proteins filtration, were subjected to a feasibility study for natural rubber (NR) effluent treatment. The highest flux recovery of 84% could be achieved by CP10-10 membrane using hydraulic cleansing and its properties are summarized as follows: 62.73º contact angle, 34.3% degree PVA surface coverage, 43.5 nm root mean square surface roughness (Rq), 30-72 nm pore size and 23% porosity. It can also be inferred that the pore size and pore size distribution gave profound influence on the membrane fouling resistance during NR filtration. In addition, all the membranes showed remarkable performances in reducing turbidity (> 99%) and colour (>97%). Reduction of 68-70% total proteins, 29-38% chemical oxygen demand (COD), 14-32% total organic carbon (TOC), 8- 11% total dissolved solid (TDS) and 7-8% conductivity were achieved by the membranes depending on the membrane properties.