AGEING MECHANISM OF PVDF FOLLOW-FIBER MEMBRANES USED IN WATER PURIFICATION PLANT

Abstract

 PVDF hollow-fiber membrane used in a water purification plant was analyzed and compared with the virgin and the artificially aged membranes in order to evaluate the aged membrane condition and to clarify the ageing mechanism. From the results of the bubble point test and the diffusive air flow test, the used membrane became more permeable to air than the virgin membrane, and the analysis of the SEM image of the membrane surface confirmed the increase of the porosity in the used membranes. Slight changes were observed in the molecular weight distribution of the polymer molecule by gel permeation chromatography (GPC) and in the crystallinity by X-ray diffraction (XRD) and attenuated total reflection-Fourier transform infrared spectrometry (ATR-FTIR). On the other hand, in the ATR-FTIR analysis, the attenuation rate of peaks for the used membranes was almost the same between the crystalline phase and the amorphous phase. Furthermore, in SEM analysis of the used membrane, a decrease in the density of PVDF structure and the rougher membrane surface were observed. These results suggested that the ageing of the PVDF hollow-fiber membrane used in a water purification plant was caused by the detachment of PVDF structure including both the crystalline and amorphous phase rather than by the change in crystalline structure or the chain scission of PVDF polymer.