复合热致相分离法制备PVDF共混膜的研究

发布时间：2018-09-14 11:31

【摘要】：聚偏氟乙烯(PVDF)作为分离膜的常用材料,广泛应用于给水工程、工业废水、医药行业、食品行业、能源行业等领域。但PVDF膜的强疏水性,导致其易于被污染,增加膜的运行成本,限制了其使用。制备PVDF膜多采用相转化法,其主要包括:非溶剂致相分离法(NIPS)、热致相分离法(TIPS)、复合热致相分离法(NTIPS)等。本文在系统研究PVDF膜的制备方法的基础上,采用了共混改性的方法对PVDF膜改性,利用NTIPS法制备了性能优良、亲水性强、非对称结构的PVDF共混膜。首先,利用流变仪考察了PVDF与己内酰胺(CPL)二元体系的流变性能,研究了PVDF百分含量、剪切速率、制膜温度等对PVDF/CPL铸膜液体系的影响。结果表明,PVDF/CPL铸膜液体系为非牛顿性流体。随着PVDF质量百分含量的增加,粘流活化能增加,非牛顿性指数减小。PVDF质量百分含量高的铸膜液体系,剪切频率对体系的影响较小,温度对其的灵敏度高,制膜过程对温度的控制需要更加精确。PVDF质量百分含量低的铸膜液体系,受剪切频率的影响较大,温度对其的灵敏度低。此研究为制备PVDF膜的工艺选定,提供了参考。其次,本文以CPL为稀释剂,PVDF与亲水性聚合物共混,采用NTIPS法制备PVDF共混膜。采用DSC法考察了亲水的聚合物与PVDF之间的相容性。利用扫描电镜分析PVDF共混膜的不同结构。通过对膜接触角的考察,进而分析膜的亲水性。分别考察了膜材料浓度、共混比例、凝固浴温度不同对膜的结构与性能的影响。研究表明,聚氧化乙烯(PEO)与聚乙烯醇(PVA)对PVDF膜的亲水改性效果较好,聚甲基丙烯酸甲酯(PMMA)亲水改性效果不明显。当高分子膜材料的浓度增加时,PVDF共混膜的膜孔径、孔隙率变小,膜的水通量降低,而膜的截留率升高。PVDF与亲水聚合物的不同比例也调控着膜的结构与性能。当PMMA含量增加,影响PVDF结晶,形成不同的支撑层结构。当PVDF与PEO共混比增加到8:2,由于PEO分子量大,与PVDF存在微观相分离,形成不同结构的皮层。当PVA含量的增加,传质加快,形成海绵状结构,同时,膜的亲水性能加强。凝固浴温度对NTIPS法制得膜的结构影响较大。随着凝固浴温度的升高,NTIPS法制备的PVDF共混膜,NIPS成膜过程占主导,导致大孔结构增加。最后,分别理论计算了PVDF/PMMA、PVDF/PEO、PVDF/PVA共混膜阻力分布。考察共混膜的耐污染性能,并进一步考察清洗、恢复效果。结果显示,PVDF/PEO与PVDF/PVA共混改性膜的耐污染性能提高,清洗效果较好。
[Abstract]:Polyvinylidene fluoride (PVDF) is widely used in water supply engineering, industrial wastewater, pharmaceutical industry, food industry, energy industry and so on. However, the strong hydrophobicity of PVDF membrane makes it easy to be polluted, increases the running cost of the membrane, and limits its use. PVDF films are prepared by phase inversion method, including non-solvent induced phase separation method, (NIPS), thermal phase separation method, (TIPS), composite thermal phase separation method, (NTIPS) method and so on. On the basis of systematically studying the preparation method of PVDF membrane, the PVDF membrane was modified by blending method. The PVDF blend membrane with excellent properties, strong hydrophilicity and asymmetric structure was prepared by NTIPS method. Firstly, the rheological properties of binary systems of PVDF and caprolactam (CPL) were investigated by rheometer. The effects of the content of PVDF, shear rate and film preparation temperature on the casting solution of PVDF/CPL were studied. The results show that PVDF / CPL casting liquid system is a non Newtonian fluid. With the increase of mass percent content of PVDF, the viscous flow activation energy increases, and the non-Newtonian index decreases. The control of temperature in the process of film preparation requires a more accurate casting liquid system with low mass percent content of PVDF, which is greatly affected by shear frequency and has low sensitivity to temperature. This study provides a reference for the process selection of PVDF films. Secondly, the PVDF blend membrane was prepared by NTIPS method with CPL as diluent and hydrophilic polymer. The compatibility between hydrophilic polymer and PVDF was investigated by DSC method. The different structure of PVDF blend membrane was analyzed by SEM. The hydrophilicity of the membrane was analyzed by investigating the contact angle of the membrane. The effects of membrane material concentration, blending ratio and coagulation bath temperature on the structure and properties of the membrane were investigated. The results showed that the hydrophilic modification effect of polyvinyl peroxide (PEO) and polyvinyl alcohol (PVA) on PVDF membrane was better than that of poly (methyl methacrylate) (PMMA). When the concentration of polymer membrane material increases, the pore size of PVDF blend membrane becomes smaller, the water flux of membrane decreases, and the membrane rejection increases. The different ratio of PVDF and hydrophilic polymer also regulates the structure and properties of the membrane. When the content of PMMA increases, the crystallization of PVDF is affected and different supporting layer structures are formed. When the blending ratio of PVDF and PEO is increased to 8: 2, because of the large molecular weight of PEO, there is a microcosmic phase separation from PVDF to form different structures of cortex. With the increase of PVA content, mass transfer accelerates, forming spongy structure, and the hydrophilicity of the membrane is enhanced. The solidification bath temperature has a great influence on the structure of NTIPS film. With the increase of coagulation bath temperature, the film forming process of PVDF blend membrane is dominant, which leads to the increase of macroporous structure. Finally, the resistance distribution of PVDF/PMMA,PVDF/PEO,PVDF/PVA blend membrane was calculated theoretically. The fouling resistance of the blend membrane was investigated, and the cleaning and recovery effects were further investigated. The results showed that the PVDF / PEO / PVDF/PVA blend modified membrane had better cleaning performance and better pollution resistance.
【学位授予单位】：宁波大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ051.893

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