Hydrophilic Modified Pvdf Membrane And Anti-pollution Performance Study

Poly (vinylidene fluoride) (PVDF) membranes are widely used in microfiltration (MF) and ultrafiltration (UF) due to their excellent chemical resistance, well-controlled porosity, and good thermal and mechanical properties. However, the higher hydrophobicity of the membrane limited its application in the fields of biotechnology and pharmacy, where the fluid phases to be treated are generally complex and heavily loaded with colloidal matters and hydrophilic membranes with better fouling resistances are required.In this article, a novel method was used to prepare hydrophilic PVDF ultrafiltration membrane. As for PVDF, C-H and C-F bond with high bond energy was difficult to cleave only by UV irradiation. To make graft polymerization easier, we incorporated a small amount of photoactive polymer PES into PVDF in the asymmetric membrane casting, then grafted hydrophilic monomers (N-vinyl-2-pyrrolidinone and 2-acrylamido-2-1-propanesulfonic acid) on the dense layer of the blend membrane under UV irradiation. Firstly, PES/PVDF blend membrane was prepared for photo grafting surface modification. As the content of PES in the blend membrane was low, the modified PVDF was expected to keep well its mechanical properties. The characteristics of the modified membrane were studied by ATR-FTIR, energy dispersive spectrometry (EDS) and contact angle. It was found that the mechanical property of the blend membrane did not change if the PES content in the blend membrane was lower then 0.5% and the contact angle of water on the membrane surface decreased with the grafting time. The modified membrane showed higher fouling resistance. First, the adsorption amount of bovine serum albumin (BSA) on the membranes decreased from 159±2μg/cm~2 to 13±2μg/cm~2 after 10 min of grafting. Secondly, the filtration of a 0.1% BSA solution showed that the modified membrane had lower BSA adsorption and better flux recovery. Compared with the non-modified PVDF membrane, the fouling degree of the blend membrane with 7 min grafting was reduced by 66% and the flux recovery after chemical cleaning increased about 32%.In our investigation of preparation of nanofiltration membrane by UV-graft polymerization on PEK-C ultrafiltration membrane, it was found that negatively charged nanofiltration membrane prepared by grafting acrylic acid (AA) performed lower retention of multi-valent cations. In this article, we firstly developed a method to prepare hydrophilic positively charged nanofiltration membrane by graft polymerization of chloromethylstyrene (CMS) onto surface of PEK-C ultrafiltration membrane and quaternary animation processes. ATR-FTIR spectra detected CMS grafted on the surface of PEK-C, and relative grafting ratio increased with irradiation time, while contact angle of water on the modified membrane surface decreased. The modified membranes showed a good retention of multi-valent cations that is a characteristic of nanofiltration. For example, the retentions to magnesium chloride and sodium chloride of the membrane grafted for 10 min under UV intensity of 3.44 mW/cm~2 was 70% and 39% at 0.4MPa, respectively.