Journal of Membrane Science 249 (2005) 21–31 Surface modification of polypropylene microfiltration membranes by the immobilization of poly(N-vinyl-2-pyrrolidone): a facile plasma approach Zhen-Mei Liu a , Zhi-Kang Xu a,∗ , Ling-Shu Wan a , Jian Wu b , Mathias Ulbricht c a Institute of Polymer Science and RIMST, Zhejiang University, Hangzhou 310027, PR China b Department of Chemistry, Zhejiang University, Hangzhou 310027, PR China c Institut f ¨ ur Technische Chemie, Universit¨ at Essen, 45117 Essen, Germany Received 19 July 2004; accepted 4 October 2004 Available online 7 January 2005 Abstract This paper describes a facile approach for the surface modification of polypropylene microfiltration membrane (PPMM) by poly(N-vinyl-2- pyrrolidone) (PNVP), which involved the physical adsorption of PNVP, followed by a plasma treatment to immobilize PNVP on the membrane surface. Chemical and morphological changes of the membrane surface were characterized in detail by attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and water contact angles measurements. Results reveal that both the plasma treatment time and the adsorbed PNVP amount have remarkable effects on the immobilization degree of PNVP. Pure water contact angle on the membrane surface decreases with the increase of PNVP immobilization degree, which indicates an enhanced hydrophilicity for the modified membranes. Static platelets adhesion experiment on the membrane surface was conducted to characterize the hemocompatibility of the PNVP-modified PPMM. The statistical amounts of adhered platelets on unit membrane area decrease significantly, which to a certain degree demonstrates that the hemocompatibility of the PNVP-modified membrane has been improved. Finally, permeation fluxes of pure water and bovine serum albumin solution were measured to evaluate the antifouling property of the PNVP-modified membranes, the results of which have shown an enhancement of antifouling property for the PPMMs. In a word, this pre-adsorption-plasma approach was found to be facile and useful in improving the hemocompatibility and the antifouling property of the PPMMs. © 2004 Elsevier B.V. All rights reserved. Keywords: Polypropylene microfiltration membrane; Poly(N-vinyl-2-pyrrolidone); Plasma treatment; Surface modification; Hemocompatibility; Antifouling property 1. Introduction For many membrane processes such as ultrafiltration and microfiltration, flux decline resulted from protein adsorption, concentration polarization, pore blocking, and gel layer for- mation, etc., is a repugnant problem, which to a great extent prevents the wide-scale applications of membrane separa- tion processes in aqueous solution treatment and biosepa- ration. A typical case is the filtration of complex fluids in biotechnology and food industries, from which proteins ad- ∗ Corresponding author. Tel.: +86 571 8795 2605; fax: +86 571 8795 1773. E-mail address: xuzk@ipsm.zju.edu.cn (Z.-K. Xu). sorb onto the surface and deposit within the pores of mem- brane, resulting in biofouling and/or flux reduction for the membrane [1]. It is reported recently that the adsorptive foul- ing could account for up to 90% of permeability losses [2]. Therefore, much attention has been paid in the past 20 years to find out the mechanism of protein adsorption, and it is now known that the electrostatic forces and the hydrophobic interactions between certain domains in a protein molecule and the hydrophobic membrane surfaces are the main fac- tors [3–5]. Up to now, it has been generally accepted that hydrophilic materials are less sensitive to protein adsorption than hydrophobic ones, the principle behind which is that hy- drophilic surface preferentially adsorb water rather than so- lutes, leaving the membrane surface with protein-resistance 0376-7388/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.memsci.2004.10.001