PVDF平板超滤膜的制备与光接枝改性研究

发布时间：2018-03-03 00:01

本文选题：平板超滤膜　切入点：聚偏氟乙烯　出处：《东北林业大学》2015年硕士论文　论文类型：学位论文

【摘要】：膜技术是21世纪最受关注的研究领域之一,应用于环保、电子、能源和生物等众多领域。随着水资源问题的日益严峻,应用于水处理领域的膜技术吸引了众多研究者的目光。限制膜技术发展的一个最重要因素是膜污染,平板超滤膜相比其他超滤膜能更好的抗污染,机械强度更好,维护清洗也非常简单,因此,平板膜可以长时间稳定的运行。聚偏氟乙烯(PVDF)因为其优异的特性,非常适合作为制备平板膜的材料。平板膜往往应用在大型水处理设备中,这就需要提高平板膜的透过性能,本研究以二甲基乙酰胺为溶剂,通过非溶剂致相转化法制备PVDF平板膜,在铸膜液中加入不同的添加剂,对膜孔的孔径和分布进行控制,并对聚合物质量分数、不同溶剂、添加剂组分和质量分数等因素对膜通过性能的影响进行研究。结果表明,铸膜液中聚合物质量分数越低,水通量越大,当PVDF质量分数为16%时,在15kPa压力下,膜通量可达92.7L.m-2.h。高分子量亲水性添加剂PVP的致孔能力很强,当其质量分数为5%时,膜通量达到152.1L·m-2·h,而未添加PVP的原始膜通量只有69.7L.m-2.h,应该将其质量分数控制在2%以下,含量过高会导致膜孔结构过于疏松,大大降低出水SDI。PEG-400则是低分子量的添加剂,可以与PVP组合,控制膜孔的孔径及分布。经过实验发现,PVDF质量分数为18%的情况下,以2%的PVP作为致孔剂,并配合甘油控制膜表面孔结构,可以在保证出水SDI的情况下,将通量提升至97.4L·m-2·h (15kPa压力下)。膜污染主要作用于膜的表面,所以通过对膜表面进行改性,可以有效的提高膜污染性能。紫外光引发接枝又是一项简单温和,效果稳定的表面改性方式。通过共混添加剂提高了膜通过性能之后,本研究通过常见紫外光源照射,以高铈离子为引发剂,N,N-亚甲基双丙烯酰胺和聚乙烯吡咯烷酮为单体,对PVDF进行了表面接枝改性。考察了光照时间、单体浓度、引发剂浓度对膜抗污染性能的影响。结果表明,光照时间不宜过长,以3mmin为宜,光照太久会造成膜通量的明显下降：MBA单体浓度不宜过高,达到0.07 mol·L/1就可以获得很好的接枝效果；由于高铈离子引发剂会发生水解,引发剂浓度不能过低,0.04 mol·L-1是最佳浓度。在以上实验条件下制备的膜片具备优秀的抗污染性能,膜片通量恢复率得到明显提升,由未改性前的40%,提升到91.3%。膜表面接触角由77.7°下降到50.0°。通过扫描电镜和表面全反射红外表征后发现,经过改性后,膜表面更加光滑,引入了具有亲水性的酰胺基团。本研究采用的两步改性方法,简单高效,能够很好的稳固提升膜通量和抗污染性能,对高性能PVDF膜的大规模生产有重要参考价值。
[Abstract]:In 21th century, membrane technology is one of the most concerned research fields, which is used in many fields, such as environmental protection, electronics, energy and biology. Membrane technology applied in the field of water treatment has attracted the attention of many researchers. One of the most important factors limiting the development of membrane technology is membrane fouling. Plate ultrafiltration membrane has better anti-fouling and better mechanical strength than other ultrafiltration membranes. Maintenance and cleaning is also very simple, so the flat membrane can run steadily for a long time. PVDF is very suitable for the preparation of flat membrane because of its excellent characteristics. Plate membrane is often used in large water treatment equipment. It is necessary to improve the permeability of the membrane. In this study, PVDF flat membrane was prepared by non-solvent phase inversion method with dimethyl acetamide as solvent. Different additives were added to the casting solution to control the pore size and distribution of the membrane. The effects of polymer mass fraction, different solvents, additive composition and mass fraction on the membrane permeability were studied. The results showed that the lower the polymer mass fraction in the cast membrane solution, the greater the water flux, when the mass fraction of PVDF was 16. Under the pressure of 15kPa, the membrane flux can reach 92.7L 路m-2.h. the high molecular weight hydrophilic additive PVP has very strong pore-forming ability. When the mass fraction is 5, the membrane flux reaches 152.1 L 路m-2 路h, while the original membrane flux without PVP is only 69.7 L 路m-2.h. the mass fraction of PVP should be controlled below 2%. Too much content will lead to the porous membrane structure, greatly reduce the effluent SDI.PEG-400 is a low molecular weight additive, can be combined with PVP to control the pore size and distribution. It is found by experiments that the mass fraction of SDI.PEG-400 is 18%, Using 2% PVP as pore-forming agent and glycerol controlling membrane surface pore structure, the flux can be increased to 97.4L 路m-2 路h ~ (-1) 路h ~ (-1) KPA under the condition of guaranteed effluent SDI. Membrane fouling mainly acts on the surface of the membrane, so the membrane surface is modified. UV-induced grafting is a simple, mild and stable way of surface modification. The surface grafting modification of PVDF was carried out using cerium ion as initiator N- N- methylene bisacrylamide and polyvinylpyrrolidone as monomers. The effects of illumination time, monomer concentration and initiator concentration on the antifouling properties of PVDF were investigated. If the illumination time is not too long, the suitable light time is 3mmin, and the membrane flux will decrease obviously when the illumination time is too long, and the monomer concentration should not be too high, and the grafting effect can be very good when the monomer concentration reaches 0.07 mol 路L / 1, because the cerium ion initiator will be hydrolyzed. The best concentration was 0.04 mol 路L ~ (-1) of initiator. The membrane prepared under the above experimental conditions had excellent anti-pollution performance, and the recovery rate of membrane flux was improved obviously. The contact angle of the film surface decreased from 77.7 掳to 50.0 掳. The surface of the film was more smooth after the modification, which was characterized by scanning electron microscope (SEM) and surface total reflection infrared spectroscopy (FTIR). A hydrophilic amide-group was introduced. The two-step modification method adopted in this study is simple and efficient, and can improve the flux and anti-fouling performance of the membrane. It has important reference value for large-scale production of high-performance PVDF membrane.
【学位授予单位】：东北林业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ051.893

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