Preparation of PET threads reinforced PVDF hollow fiber membrane
Introduction
Hollow fiber membranes, due to their excellent performances, have been used in wastewater and drinking water treatments, pretreatment of seawater reverse osmosis and so on [1], [2], [3], [4], [5], [6]. However, the most popularly used UF and MF hollow fiber membranes nowadays, which are composed of skin layer and support layer, are prepared by the immersion-precipitation method. Normally, these hollow fiber membranes have high permeability but low mechanical endurance. The frequently broken hollow fiber membranes due to their low mechanical properties may decrease the production quality and increase the cost. The membrane with high separation, permeability and excellent mechanical properties needs to be developed.
Some research studies have been done to improve the mechanical properties of the hollow fiber membranes [7], [8], [9], [10]. The works majorly focused on the optimization of membrane preparation conditions and material concentrations in the dope solution to raise membrane mechanical properties by affecting the micro phase separation or molecule orientation during the membrane formation process. However, very limited improvements were achieved. Besides, a more effective method is revealed by a patent of Zenon Environmental Inc. [11], in which the asymmetric membrane composing of a tubular polymer film and a tubular braid on which the film is supported is developed. The braid used can supply a high mechanical strength. It is because the tubular braid is exposed on the inner surface of the membrane and has a rough porous structure, the membrane pores are easily contaminated and jammed, and also the cleaning process becomes more difficult compared to the normal membranes.
Different from these previous methods, a new idea will be practised in this study. Reinforcement threads as the reinforcement material are incorporated into hollow fiber membrane. To minimize the effects of threads on the process of membrane structure formation and membrane separation performances, in addition to the excellent tensile/rupture strength and ductility, the reinforcement threads should have an excellent resistance to all solvents in the formula of membrane fabrication, wettability with the membrane dope solution and small diameter. Based on the above analysis, polyvinylidene fluoride (PVDF) will be used as membrane material, which is commonly used in ultrafiltration (UF) and microfiltration (MF) applications. PET multifilament will be used as the reinforcement material. The mechanical properties of the fabricated hollow fiber and the effects of the reinforcement on the membrane structure and membrane filtration properties will be studied in the paper.
Section snippets
Materials
Polyvinylidene fluoride (PVDF) was obtained from Chenguang Research Institute of Chemical Industry (Sichuan, China). N,N-dimethylacetamide (DMAc) used as solvent was obtained from Tiantai Fine Chemical Co. Ltd (Tianjin, China). Polyvinylpyrrolidone (PVP, K30, Mw = 30,000) was purchased from Damao Chemical Regent Factory (Tianjin, China). The mass of PVP used as additive was about 20% of PVDF. Polyester multifilament (100 dtex/48 fil, 3.5 cn/dtex, elongation ratio of 30%) was used as reinforcement
Morphology of reinforced PVDF hollow fiber
Two kinds of PVDF hollow fibers, one without PET threads and the other one with 3 threads in (as shown in Fig. 3a and b), were prepared under the same conditions to investigate the effect of PET threads on the membrane structure. It was shown in Figs. 3a, b and 4 that both membranes are composed of skin layer and support layer (finger-like structure). The PET threads lie in the support layer in axes direction. As shown in Fig. 3, Fig. 4, the PVDF had an adequate contact with the filaments,
Conclusion
PET threads reinforced PVDF hollow fiber membranes were prepared. The influences of PET threads on the membrane properties were investigated. The tensile/rupture strength of the reinforced membranes was significantly improved to 10 MPa. PET threads, not much engaging the phase-separation process of membrane formation, had little effects on membrane separation-related properties. The membrane mechanical properties and its separation and penetration properties became two nearly independent
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