Pvdf Hollow Fiber Membrane Surface Modification

Due to the hydrophobicity of poly(vinylidene fluoride) (PVDF), the application of PVDF membrane was limited. In this paper, we adopt a simple chemical modification method for the surface functionalization and grafting of polar monomers onto PVDF membranes, which provides excellent hydrophilicity to the polymeric surfaces.Firstly, the porous membranes of hydrophobic polyvinylidene fluoride were pretreated by a strong alkali solution containing an oxidizing agent to introduce a polar group on the membrane surface. The surface compositions of the pretreated PVDF membrane were determined by Fourier transform adsorption spectrum (FTIR) and X-ray photoelectron spectroscopy (XPS). From the FTIR and XPS results it was evident that HO-C groups were formed. Optimum conditions for pretreatment were ..found to be [KOH] = 2.3mol/L, KMnO4% =3wt%, T=50 C and t =10min. Secondly, the grafted membranes were prepared by grafting 2-Acrylamido-2-methyl propane sulfonic acid (AMPS) on pretreated membranes using cetric ammonium nitrate (CAN) as an initiator in the aqueous medium. The surface compositions of the grafted membranes were determined by Fourier transform adsorption spectrum (FTIR) and X-ray photoelectron spectroscopy (XPS). And the morphology of the grafted membranes was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM).Water content test revealed that grafting AMPS on PVDF membrane was an effective method to improve the hydrophilicity of PVDF membrane. It was found that the flux of water decreased with increasing surface concentration of the grafted AMPS polymer, while the pore size remained almost unchanged. The grafted membranes were capable of rejecting an anionic dyestuff.In common with other polyelectrolytes, the conformation of grafted AMPSA polymeric chains is sensitive to environmental factors such as pH and ionic strength (I). For the conformation of AMPSA polymeric chains, fluxes through the grafted membranes were very sensitive to the solution ionic strength and also to the solution pH. At higher pH or lower /, the flux through the grafted membranes was lower; conversely, the flux through the grafted membranes increased as pH decreased or I increased.