The effects of hydroxyapatite nano whiskers and its synergism with polyvinylpyrrolidone on poly(vinylidene fluoride) hollow fiber ultrafiltration membranes

Abstract

By introducing hydroxyapatite (HAP) nano whiskers as well as polyvinylpyrrolidone (PVP), poly(vinylidene fluoride) (PVDF)/PVP/HAP hollow fiber membranes were fabricated with the wet spinning method. The aqueous solution containing 90 wt% N-methyl-2-pyrrolidone (NMP) is used as bore liquid. The effects of two additives and the synergism on the morphologies, surface properties, permeation performances, antifouling ability and mechanical properties of the PVDF/PVP/HAP membranes were characterized by numerous state-of-the-art analytical techniques, and reasonably elucidated accompanying with precipitation kinetics and shear viscosity of dopes. The results show that with the addition of HAP, the finger-like structure of PVDF/PVP/HAP membranes is gradually suppressed and replaced by sponge-like structure, and the hydrophilicity is evidently improved. The hydraulic permeability J_w firstly increases from 224.2 of M-1 to 549.1 L M⁻² H⁻¹ bar⁻¹ by adding 1.0 wt% HAP nano whiskers of M-2, and then decreases to 425.9 and 316.3 L M⁻² H⁻¹ bar⁻¹ for M-3 and M-4. The rejections of three proteins and humic acid range from 31.4% to 98.4%, and slightly decrease as HAP content increases in the membranes. The mechanical properties of the membranes are markedly improved with the addition of HAP nano whiskers. The membranes containing dual additives have higher permeability and mechanical strength than those of the fibers containing either single additive, implying the synergism of them in improving membrane properties.