制膜液黏度对单皮层PVDF中空纤维膜纺制的影响

以二甲基乙酰胺(DMAc)为溶剂,制备聚偏氟乙烯(PVDF)浓度为15%的制膜液,考察了DMAc同时作为内凝胶浴时膜结构的变化.为保持纺膜过程中的稳定性,分别考察了添加剂LiCl、水以及表面活性剂对制膜液黏度的影响.实验发现添加LiCl可以大大提高制膜液的黏度,而水作为添加剂时对黏度的影响与制膜液本身的浓度有关.在不提高制膜液浓度的基础上,通过提高制膜液黏度克服了膜在纺制过程中的不稳定问题,得到阻力较小的,指状孔贯穿的单外皮层中空纤维膜.     

扩散致相转化法制备结晶性聚合物多孔膜

介绍了扩散致相转化法制备结晶性聚合物多孔膜的研究现状。其三元等温成膜体系的相图包含液-液分相和固-液分相两种相分离方式,是理解成膜过程的重要工具,总结了成膜机理和膜的结构形貌：单纯S-L相分离生成粒子状对称膜结构;单纯L-L相分离生成蜂窝状非对称膜结构;两种相分离方式竞争发生将生成多样的混合膜结构。铸膜液浓度、非溶剂种类、铸膜溶剂组成、凝胶浴组成、制膜温度是影响膜结构形貌的主要因素。     

纤维编织管增强型中空纤维膜研究

采用二维编织技术将聚丙烯腈(PAN)长丝编织成中空纤维编织管作为增强体,分别以聚丙烯腈(PAN)和聚偏氟乙烯(PVDF)为成膜聚合物,N,N-二甲基乙酰胺(DMAc)为溶剂,聚乙烯吡咯烷酮(PVP)为添加剂,调制铸膜液,采用同心圆挤出-涂覆法制备了PAN纤维编织管同质增强型PAN中空纤维膜和异质增强型PVDF中空纤维膜.研究表明,所得PAN纤维编织管增强型中空纤维膜断裂强度最大可超过75 MPa,在伸长率10%范围内,表面分离层与增强体之间界面结合良好;表面分离层具有类似于非对称膜的结构,铸膜液可浸入纤维编织管纤维空隙中,铸膜液浸入部分固化后未影响膜的通透性能;随成膜聚合物浓度增加,膜纯水通量减小,牛血清白蛋白(BSA)截留率增大;随添加剂PVP浓度增加,膜的纯水通量先增大后减小,在8 wt%左右达最大值,BSA截留率随PVP浓度增加而单调增加;同质增强型中空纤维膜界面结合程度优于异质增强型.     

TEP-DMAc混合溶剂对PVDF膜性能的影响

利用非溶剂相转化法(NIPS)制备聚偏氟乙烯(PVDF)膜,考察了聚乙二醇(PEG200)与N,N-二甲基乙酰胺(DMAc)的质量比对膜分相速率和膜性能的影响,讨论了以磷酸三乙酯(TEP)和DMAc的混合液作溶剂对PVDF膜凝胶速率、膜结构和膜通量的影响。结果表明:PEG200的加入减弱了溶剂对聚合物的溶解能力,但铸膜液的分相行为由延迟分相转变为瞬时分相,膜通量提高。随着混合溶剂中TEP含量的增大,铸膜液的黏度增大,分相速率减慢;在高质量比m(TEP)/m(DMAc)时,膜表面的孔增多,指状孔膜结构逐渐消失,整个膜截面呈海绵状,膜通量变大,力学性能提高。     

氯化锂为添加剂制得的疏水聚偏氟乙烯不对称微孔膜的形态结构及其膜蒸馏性能

结合膜的形态结构研究了以 LiCl为添加剂制得的疏水 PVDF膜的膜蒸馏性能。与来用水溶液高分子添加剂制得的PVDF微孔膜相比,膜蒸馏性能有了较大提高,尤其具有更高的截留率。制得的微孔膜的蒸馏通量已接近商品膜的膜蒸馏通量,表明以LiCl为添加剂制得的PVDF疏水微孔膜是一种适用于膜蒸馏的较理想的疏水微孔膜。     

凝固浴温度对PVDF铸膜液相分离过程和膜结构的影响

采用皮-亚两步凝胶成膜机理探讨了凝固浴温度对PVDF铸膜液的相分离行为及其膜结构的影响.采用浊度法测定不同温度时铸膜液体系的热力学性质,光透射仪测定不同凝固浴温度时沉淀速率对膜的形态和性能的影响.结果显示:皮层的生成主要受热力学性质控制,随着凝固浴温度的提高,皮层由液固分相转变为液液分相,延时时间缩短,皮层由相互融合的球粒致密结构转变为多孔结构.亚层的生成主要受皮层结构和溶剂/非溶剂相互扩散的影响,膜亚层主要发生液液分相;随凝固浴温度升高,分相速率加快,大孔发展更充分,膜的孔隙率和气通量提高,但结晶度降低.     

溶剂浓度对PVDF相转换膜大孔结构的影响

提出决定大孔能否发展的初始分相点处溶剂浓度临界点的概念 ,认为初始分相点处较高的溶剂浓度有利于大孔的发展 ,溶剂浓度低于一定的界限后 ,大孔停止发展 ,转为海绵状结构 .实验考察了不同凝胶液组成下制得的PVDF中空膜的结构 ,建立了相应的传质模型 ,模拟不同制膜条件下初生态膜内的组成分布情况 ,根据初始分相点处溶剂浓度临界点的概念 ,预测膜的形态结构 .模拟结果与相应制膜条件下的电镜照片有很好的对应关系 ,证明了上述大孔形成机理的正确性 .     

小分子醇对PVDF／PFSA共混膜凝胶动力学、膜结构及膜性能的影响

以小分子醇为添加剂,研究了小分子醇对聚偏氟乙烯(PVDF)/全氟磺酸(PFSA)共混超滤膜凝胶动力学、结构与渗透性能的影响.结果表明:在PVDF/PFSA铸膜液中添加乙醇时,其凝胶速率随乙醇浓度的增加而加快,超滤膜通量随乙醇浓度的增加而增大;而当添加相同浓度的4种小分子醇时,初始凝胶速率差别不大,20 s后添加乙醇的铸膜液的凝胶速率最大;添加小分子醇后超滤膜的水通量大小顺序为:异丙醇<甲醇<乙醇<正丁醇.SEM照片显示在铸膜液中添加5%乙醇所制备的共混超滤膜具有较为圆整的内腔结构与均匀的孔结构.     

聚乙二醇对聚醚砜超滤膜微结构和性能的影响

通过改变铸膜液中添加剂PEG的含量，测试了当铸膜液中PES的质量分数为0．21，凝固浴(DM—SO／H2O体系)中DMSO的质量分数为0．10时，所成膜的水通量和尿素、肌酐去除率。研究了PES／DMSO体系中小分子添加剂PEG作用的规律。     

ZrO2纳米粒子原位杂化PVDF膜的制备及其抗污染性能

针对传统聚合物膜抗污染性差的问题,本文从杂化膜结构设计出发,提出将ZrO2纳米粒子的原位制备和聚偏氟乙烯(PVDF)相转化成膜过程有机结合的制膜新方法.该方法将阴离子交换树脂引入到N,N-二甲基甲酰胺(DMF)中,以氧氯化锆为原料,利用阴离子交换树脂提供的―OH与无机盐的阴离子进行交换,得到ZrO2纳米粒子均匀分散的N,N-二甲基甲酰胺溶胶体系.随后将PVDF聚合物溶解到所得的N,N-二甲基甲酰胺溶胶体系中,获得均一、透明的铸膜液.利用X射线光电子能谱(XPS)和透射电子显微镜(TEM)对杂化膜中锆的存在状态和分散性能进行了表征.结果表明,ZrO2纳米粒子均匀分散在PVDF基体中,并且形成的纳米粒子的粒径约为10-20 nm.通过粘度、分相速度和膜形态的测定,研究了成膜机理.结果表明,ZrO2纳米粒子的引入加速了铸膜液成膜过程的分相速度.杂化膜的亲水性能通过接触角测定仪进行了评价.并选择以牛血清蛋白为代表模拟污染物,考察了杂化超滤膜的抗污染性能.结果表明,原位形成的ZrO2纳米粒子显著提高了膜的亲水性,减少了膜对蛋白质的吸附.这种将ZrO2纳米粒子的原位制备和PVDF相转化成膜过程有机结合的制膜新方法在有机-无机杂化膜的制备领域具有显著意义.     

Correlation between macrovoid formation and the ternary phase diagram for polyethersulfone membranes prepared from two nearly similar solvents

The morphological structure of membranes prepared from two nearly similar systems consisting of water/N,N-dimethylacetamide (DMAc)/polyethersulfone (PES) and water/N-methyl-2-pyrrolidone (NMP)/polyethersulfone (PES) has been studied. The morphology of the prepared membranes showed that both systems exhibit an instantaneous liquid–liquid demixing that leads to the formation of macrovoids in the resulting structures. Nevertheless, the resulting macrovoid structures were contrary to the generally accepted concepts concerning macrovoid formation. The membranes morphologies showed that in spite of better miscibility between water and DMAc, which must promote the formation of channel- and finger-like structures, more sponge-like structures were observed in membranes prepared from the water/DMAc/PES system compared to those prepared from the water/NMP/PES system. To find the source of this unexpected phenomenon, the complete ternary phase diagrams consisting of theoretical binodal curves, vitrification boundaries, and gelation boundaries were constructed for both systems and it was shown that gelation process occurs earlier in the water/DMAc/PES system compared to the other system, which inhibits the growth of macrovoids in this system.     

溶剂对PVDF铸膜液相转化和微孔膜皮-亚两层结构的不同影响

采用皮-亚分步凝固成膜机理分析了3种不同溶剂对聚偏氟乙烯(PVDF)铸膜液相转化和膜结构的影响,采用浊度法测定铸膜液体系的热力学性质,沉淀速度采用光透射仪测定.结果显示,3种膜的皮层分相主要由热力学性质控制,均发生延时液固分相,生成了相互融合的球粒组成的致密皮层.3体系的亚层分相行为由动力学扩散过程控制;对于二甲基亚砜(DMSO)、N,N-二甲基乙酰胺(DMAc)体系亚层发生瞬时液液分相,结晶化对动力学过程影响小,表现为光透射曲线上分相时间t2短,生成了大孔结构为主的亚层,膜厚度、孔隙率和气通量均高、结晶度低;N,N-二甲基甲酰胺(DMF)体系亚层发生延时液液分相,结晶化对动力学过程影响大,t2长,生成蜂窝状孔结构亚层,其膜厚度、孔隙率和气通量较低,但膜的结晶度高.     

INFLUENCE OF ALCOHOL-BASED NONSOLVENTS ON THE FORMATION AND MORPHOLOGY OF PVDF MEMBRANES IN PHASE INVERSION PROCESS

Through the preparation of PVDF membranes using various nonsolvent coagulation baths following the phase inversion process, the influence of alcohol-based nonsolvents on the formation and structure of PVDF membranes were investigated. The light scattering and light transmission measurements were used to characterize the equilibrium phase diagram and the gelation speed, respectively. The locations of the crystallization-induced gelation boundaries for various systems and precipitation processes were explained from the corresponding thermodynamic and kinetic parameters. It was found that the better affinity between alcohol-based nonsolvents and DMAc solvent caused the gelation boundaries further away from the PVDF-DMAc axis with the coagulation bath varying from water, methanol, ethanol to iso-propanol. Due to the lower exchange rate of DMAc and alcohols, the delayed demixing took place for the membrane-forming using alcohols as baths, and the delayed time became longer when the coagulation bath was changed from methanol, ethanol to iso-propanol. The characterization results of membranes indicate that the influence of nonsolvents on the phase diagram and the precipitation process are in agreement with those on the membrane morphology. The better thermodynamic stability and a low exchange diffusion rate of PVDF/DMAc/alcohols favor the liquid-solid phase separation in gelation process, and therefore yield the membranes with a porous upper surface, a particular bottom surface and symmetrical structure.     

PVDF亲水复合膜的制备及表征

聚偏氟乙烯(PVDF)膜材料存在强疏水性的缺陷,亲水化改性是解决该问题的主要途径。以PVDF为基膜材料、聚乙烯醇(PVA)为共混材料、N,N-二甲基乙酰胺(DMAc)为溶剂,采用相转化法制备PVDF/PVA复合膜。考察了复合膜的PVDF/PVA共混比、固含量、低分子化合物添加剂、聚合物添加剂等非溶剂添加剂对复合膜接触角的影响。结果表明,当PVDF/PVA共混比为7/3,固含量为13%时,制备的复合膜接触角为22.92°;当添加剂为无水氯化锂、纳米二氧化硅、聚乙烯吡咯烷酮(PVP)时,复合膜接触角分别从53.12°、30.51°和41.89°都降低到了0°,亲水性提高,其中纳米二氧化硅作为添加剂时复合膜亲水性最好;当添加剂为丙三醇、PMMA、PEG时,复合膜接触角都增大,亲水性变差。     

THE INFLUENCE OF PEG MOLECULAR WEIGHT ON MORPHOLOGIES AND PROPERTIES OF PVDF ASYMMETRIC MEMBRANES

The preparation and properties of asymmetric poly(vinyldiene fluoride)(PVDF)membranes are described in this study.Membranes were prepared from a casting solution of PVDF,N,N-dimethylacetamide(DMAc)solvent and water- soluble poly(ethylene glycol)(PEG)additives by immersing them in water as coagulant medium.Experiments showed that when PEG molecular weight increased,the changes in the resultant membranes' morphologies and properties showed a transition point at PEG6000.This indicated that PEG with a relati...     

两亲性梳状聚醚硅氧烷对相转化法聚偏氟乙烯多孔膜的共混改性作用研究

以聚醚链段为侧链的两亲性梳状聚醚硅氧烷(ACPS)为改性剂,研究了相转化法制备聚偏氟乙烯(PVDF)多孔膜的改性效果与机理.采用SEM、XPS、接触角、水通量等考察了ACPS对膜结构与性能的影响.研究发现,ACPS在相转化成膜过程中不流失,随着制膜液中ACPS含量的增加,相分离速度降低,膜中微孔由指状结构向蜂窝状结构发展,膜强度提高,亲水性显著提高.提出了ACPS在膜表面的富集现象和在膜中的稳定性机理和模型.结果表明,两亲性梳状聚醚硅氧烷在原理上是一类适合于相转化法制备聚合物微孔膜表面亲水化改性的有效物质.     

Preparation and characterization of polyvinylidene fluoride (PVDF) hollow fiber membranes

Polyvinylidene fluoride (PVDF) hollow fiber membranes were prepared by dry/wet and wet phase inversion methods. In spinning these PVDF hollow fibers, dimethylacetamide (DMAc) and polyvinyl pyrrolidone (PVP) were used as a solvent and an additive, respectively. Water was used as the external coagulant. Water or ethanol was used as the internal coagulants. The membranes were characterized in terms of water flux, molecular weight cut-off for the wet membranes. Gas permeation fluxes and effective surface porosity were determined by a gas permeation method for the dried membranes. The cross-sectional structures were examined by scanning electron microscopy. The effects of polymer concentration, air-gap, PVP molecular weight, PVP content in the polymer dope, and the internal coagulant on the permeation properties and membrane structures were examined. Highly permeable PVDF hollow fiber membranes could be prepared from a polymer dope containing low molecular weight PVP and using ethanol as the internal coagulant.     

Effect of surfactants on the structure of PMMA membranes

In this work, the role played by surfactants in the formation of PMMA membranes was investigated. For a wet inversion process with PMMA as polymer, acetone as solvent, and water as coagulant, delayed demixing was observed and the resulting membrane possessed a sponge-like structure. Adding 1.8 vol% of Tween 80 in the casting solution (PMMA + acetone) could shift the PMMA/acetone/water system from delayed demixing to instantaneous demixing and could induce macrovoids with small pin-holes on the membrane surface. It was found that the affinity of surfactant for coagulant is crucial for the enhancement of the formation of macrovoids. When water was the coagulant, adding the surfactants with high water solubility in PMMA/acetone solution can enhance the formation of macrovoids while adding the surfactants with low water solubility has no effect. On the other hand, for a lipophilic coagulant such as n-hexane, lipophilic surfactants were more effective in changing membrane structure than hydrophillic surfactants. In addition, a mechanism describing the role of surfactants in the formation of macrovoids is proposed: the addition of appropriate surfactants can enhance the affinity between solvent and coagulant, resulting in a shift from delayed demixing to instantaneous demixing, and macrovoids can then be induced.