Preparation And Characterization Of PH Sensitive Polyurethane Blend Membranes

The polyurethane(PU) materials possess many advantages, such as excellent tensile strength, better biocompatibility, low temperature resistance, acid-proof, alkali-proof and designable molecule etc. As a result PU is considered to be the ideal material of base membrane used to prepare the pH sensitive membrane. The studies on the poly-ether-polyurethane(PEU)/polyethersulfone(PES), polyester-polyurethane(PSU)/polyeth-ersulfone(PES), polyvinylidene fluoride(PVDF)/polyethersulfone (PES) blend base membranes and their separation properties were fulfilled at the first stage of this work. Then the pH sensitive membranes were prepared by UV grafting acrylic acid(AAc)onto the blend base membranes with better performance. The work that combined with blend method and UV grafting method has certain significance in preparation novel membranes. In this work, adopting PEU as basal phase, and other polymers such as PAN or PES as dispersed phase, the preparing membrane technology were studied by L-S phase-inversion method using N,N-dimethylformamide (DMF) as solvent, in the presence of polyethylene glycol (PEG) 600 as addictive. Then based the technology, the PEU or PSU blend base membranes were prepared by L-S phase-inversion method with PEU or PSU as the basal phase, PES as the dispersed phase, DMF as solvent, and PEG600 as addictive. The effects of blending ratio, polymer concentration and addictive concen-tration upon properties of membranes were studied in order to prepare membranes with better separating properties. At the same time another type of blend base membrane with better separating properties was prepared by using PVDF as the basal phase, PEU as the dispersed phase, PEG as additive, N, N-dimethyl acetamide (DMAc) as solvent. Afterwards, the grafting membranes were prepared by UV photografting acrylic acid onto the blend base membranes with benzophenone as initiator. The structures were characterized by enviromental scanning electric microscope (ESEM). The results confirmed that the PEU/PES blend membrane had the structure with interfacial micro-void, but the PSU/PES blend membrane had the asymmetric structure. Owing to the structural differences, the two types of blend base membranes had different separating performances and mechanical properties. The characterized results of chemical stability showed that PEU/PES blend membranes possessed better acid-proof and alkali-proof advantages, but PSU/PES blend membranes did not possess the advantages, which restrict their application in preparation of pH sensitive membrane. Fourier transform infrared spectrum (FTIR) was used to analyze the surface component change of the grafting membranes, the results showed that the spectrum of grafting membranes had an obvious carbonyl group, C=O, character peak value, and the base membrane did not. The measurement of water flux of grafting membrane in different pH value proves that grafting membrane had pH sensitive effect. The ESEM photos confirmed that the membrane pores, after grafting, were covered by a grafting layer, and the surface of membrane became rougher, which showed that the membrane had a grafting layer. The crystallinity of the base membranes and grafting membranes was analyzed by X-ray diffractometer(XRD). After the membranes were grafted with AAc, the character peaks of the membranes were not changed but the crystallinity decreased with the grafting time. Meanwhile the influence of grafting rate upon the membrane properties was studied. The results showed that, under low grafting rate (<0.5%), grafting membrane did not have an obvious pH sensitive effect; under the condition of high grafting rate(>1%), grafting membrane had an obvious pH sensitive effect and the smaller contact angle. By characterizing the ability of the membrane antifouling for protein adsorption, the ability of antifouling had certainly been improved after grafting modification.