【作者】 张平允；

【导师】 许振良；

【作者基本信息】 华东理工大学 ， 材料化学工程， 2014， 博士

【摘要】 超滤膜已广泛应用于生物、医药、食品、血液处理、废水和超纯水等方面。作为性能优良的新型聚合物膜材料,聚偏氟乙烯(PVDF)具有优良的化学稳定性、热稳定性、机械稳定性以及低介电常数、低表面能、耐射线、紫外线辐射等性质,近年来在膜分离技术中的应用越来越广泛。但是,PVDF极低的表面能导致其可润湿能力很差,在分离油/水体系(尤其是含蛋白质或活性生物体的溶液)时,容易发生膜污染。膜污染易导致膜分离性能下降,使用寿命缩短,操作成本增加。因此,如何提高PVDF的亲水性、降低膜污染及对膜结构调控一直是研究的热点之一。本文采用小分子表面活性剂Tween-80和两亲共聚物大分子表面润湿剂调控PVDF亲水膜的结构,并对其性能进行表征。优化PVDF平板膜制备方法,制备出渗透性能良好、机械性能高的PVDF中空纤维亲水超滤膜。论文研究结果如下：首先,选用Tween-80和H2O为混合添加剂,在纯水凝胶浴中采用非溶剂致相(NIPS)法制备PVDF平板膜。动态光散射(DLS)结果表明,铸膜液中的非溶剂H20被Tween-80在DMAc中形成的反胶束增溶,形成反胶束的“水池”；Tween-80的极性基团与H2O之间的相互作用提供了PVDF与反胶束疏水外壳之间作用力的平衡力,从而提高了铸膜液的热稳定性；PVDF膜的通量、机械强度和截留等均提高,其结果如下：在适宜的制膜条件下制备的PVDF膜在0.1MPa操作压力下的纯水通量为192L·m-2·h-1;对牛血清(BSA)和葡聚糖(Dextran, MW70K)的截留率分别为88.3%和83.8%；断裂强度为1.3MPa、断裂伸长率为42.2%、杨氏模量为32.2MPa。固定铸膜液中Tween-80的含量(3.0wt.%)不变,当增加非溶剂H2O的含量时,PVDF膜纯水通量分别增加了1.7倍(60℃C铸膜液制膜)和2.3倍(室温250C铸膜液制膜)；PVDF膜的机械强度和接触角均随非溶剂H2O含量的增加而增加,但PVDF膜对BSA和Dextran的截留率变化不大。其次,通过改变凝胶浴组成和铸膜液温度,研究了Tween-80和H2O混合添加剂对PVDF平板膜的结构调控路径,并从PVDF-DMAc-Tween-80-H2O体系制得具有优良机械性能和双连续结构的PVDF亲水膜。选用的凝胶浴为乙醇-水混合凝胶浴(50：50,质量比)和纯乙醇凝胶浴,重点研究了Tween-80和H2O混和添加剂的组成、铸膜液温度和凝胶浴组成对铸膜液物理-化学性能和PVDF膜结构性能的影响。结果表明,凝胶浴组成决定了铸膜液的液液分相和液固分相的顺序和范围,而Tween-80和H2O混和添加剂和铸膜液温度影响了铸膜液的凝胶速率。凝胶过程中,Tween-80反胶束增溶的非溶剂H2O从铸膜液内部扩散,导致铸膜液凝胶速率加快和Tween-80的亲水基团向膜表面的迁移。铸膜液在纯乙醇凝胶浴中的延迟分相有利于树叶状多孔表面和膜断面针状纳米晶粒的形成。制得的PVDF平板膜的通量和亲水性都明显改善。而铸膜液在乙醇-水混合凝胶浴中则呈现较短时间的延迟分相,即液国分相和液液分相同时进行。Tween-80和H20混合添加剂的存在、高温铸膜液和乙醇-水混合凝胶浴的共同作用,导致PVDF主要结晶晶型是a-β杂化晶(结晶度为59.1%)。此外,为了解决Tween-80(?)舌性高、易溶于水、在PVDF膜制备或者PVDF膜使用过程中容易流失的问题及更好调控PVDF膜结构,采用聚乙二醇单甲醚甲基丙烯酸甲酯(PEGMA)与甲基丙烯酸甲酯(MMA)为反应单体,合成了Mn和Mw分别为66,500g/mol和34,200g/mol的两亲嵌段共聚物P(PEGMA-r-MMA),并对其结构和化学组成进行了表征；采用简单共混法,将P(PEGMA-r-MMA)反应原液(包括两亲共聚物、未反应的单体和溶剂的混合物)直接与PVDF共混,溶于TEP-DMAc (70:30,质量比)混合溶剂中,形成铸膜液,制备了结构和性能良好的PVDF-P(PEGMA-r-MMA)共混超滤膜；对铸膜液物理化学性能进行了表征,结果表明,含P(PEGMA-r-MMA)两亲共聚物的PVDF铸膜液中形成了PVDF-P(PEGMA-r-MMA)大分子聚集体。该大分子聚集体的存在导致铸膜液微观构象调整、表面张力下降、凝胶速率加快和粘度增加；讨论了反应原液的含量和凝胶浴组成对PVDF膜结构和性能的影响。结果表明,PVDF-P(PEGMA-r-MMA)大分子聚集体调控了PVDF-P(PEGMA-r-MMA)共混超滤膜的结构,且共混膜有效孔径μ分布变窄；截留分子量(MWCO)和牛血清(BSA)恢复通量均随P(PEGMA-r-MMA)两亲共聚物含量的增加而增加。随后,为了克服简单共混法形成的大尺寸PVDF-P(PEGMA-r-MMA)大分子聚集体(粒径尺寸：100～200nm)对PVDF膜调控结构和性能改善的限制,采用原位自由基聚合反应法制备出小尺寸(粒径尺寸：0-10nm)、窄分布的PVDF-P(PEGMA-r-MMA)大分子聚集体,以强化P(PEGMA-r-MMA)两亲共聚物对PVDF膜结构的调控,并讨论了PVDF-P(PEGMA-r-MMA)大分子聚集体对PVDF膜机械强度和抗污染性能的影响。DLS和扫描电镜(SEM)结果表明,原位自由基聚合反应后的PVDF-TEP-DMAc-PEGMA-MMA铸膜液体系中形成了窄分布、小尺寸的大分子聚集体；铸膜液表面张力下降、凝胶速率加快及粘度增加；制得的PVDF膜除具有窄分布的有效孔径μ和截留分子量(MWCO)外,其μ和MWCO均随铸膜液中添加的单体混合物含量的增加而增加。结果表明,原位自由基聚合反应法增强了PVDF膜的机械强度(其良好的断裂强度、断裂伸长率和杨氏模量分别为：8.8MPa、343%和229MPa)、改善了PVDF膜正反面的亲水性；PVDF膜的主要结晶晶型是α-β杂化晶(以β晶型为主),且随铸膜液中单体混合物含量的增加,膜的结晶度从56.1%增加至81.4%。原位自由基聚合反应后的PEGMA、MMA单体更好地调控了PVDF膜结构：构成膜海绵状断面的聚合物纳米晶粒由条纹状转化为球状。最后,在前文研究的基础上,采用实验室自制的活性更高的聚二甲基丙烯酸四氢呋喃酯(PTMGDA)代替MMA与PEGMA进行原位自由基聚合反应,制备PVDF中空纤维超滤膜。讨论了原位自由基聚合反应后的PVDF-TEP-DMAc-PTMGDA-PEGMA-PVP铸膜液体系的物理-化学性能变化,及形成的PVDF-P(PTMGDA-r-PEGMA)-PVP大分子聚集体对PVDF中空纤维膜结构调控及其渗透性能、机械强度和抗BSA污染性能的影响。结果表明,固定铸膜液中PTMGDA、PEGMA单体混合物含量不变,随着铸膜液中聚乙烯吡咯烷酮(PVP)的含量从1.0wt.%增加至3.0wt.%,PVDF中空纤维膜的海绵状断面结构中出现圆形孔道,而且构成海绵状结构的纳米聚合物晶粒的厚度增加、排列疏松,且膜的纯水通量从15.7L.m-1.h-1增加至60.2L.m-1.h-1,但PVDF膜的机械强度和对Dextran (40K和70K)的截留率变化不大；膜的接触角从78.8°降至65.2°,BSA通量恢复率(FRR)随PVP含量的增加而增加；原位自由基聚合反应后形成的P(PTMGDA-r-PEGMA)两亲共聚物与添加的PVP添加剂协同调控了PVDF中空纤维膜的结构、通量、亲水性和机械性能,并制得可应用于废水处理、生化分离等领域的PVDF中空纤维膜。更多还原

【Abstract】 Ultrafiltration has been widely applied not only in the biological products, pharmaceutical products and food industry; but also used for blood, wastewater treatment and ultra pure water preparation. Because of its competitive mechanical properties, thermal and chemical stability, radiation resistance, etc. As one of the most popular materials for membranes preparation, polyvinylidene fluoride (PVDF) has earned lots of attention. However, PVDF membranes possess high hydrophilicity, which leads to poor wetting ability and prone to fouling, especially in the oil/water separation system, including protein or organism. This results in decreasing of performance properties, reducing the membrane life and increasing the operation cost. Thus, the fine configurations modulation of PVDF membranes with excellent hydrophilicity and high performance are always highly sought after. The self-assembled of surfactants with various molecular weights (Tween-80and amphiphilic copolymer) in organic solvents was utilized to tune the hydrophilicity, morphology and performances of PVDF membranes. Then, after optimization of preparation parameters of flat sheet PVDF membrane preparation, PVDF hollow fiber membranes possessed good permeability, hydrophilicity and excellent mechanical properties were successfuly fabricated. The results were as follows.Firstly, PVDF membranes were fabricated by non-solvent induced phase separation (NIPS) process using Tween-80and H2O as mixture additive from both60℃and room-temperature (RT) casting solution. PVDF membranes revealed improved pure water flux (PWF), enlarged mechanical properties and well Bovine serum albumin (BSA) and Dextran rejection as a result of addition of H2O into the PVDF-DMAc-Tween-80system. The PWF of resultant PVDF was192L·m-2·h-1with0.1MPa operation pressure, and its rejection of BSA (MW67K) and Dextran (MW70K) were88.3%and83.8%, respectively. Its break strength, elongation at break and Young’s modules were1.3MPa,42.2%and32.2MPa, respectively. The PWF increased to1.7times (prepared with60℃casting solution) and2.3times (prepared with ambient temperature casting solution) after addition of H2O into the casting solution. Besides, PVDF membranes’mechanical properties and dynamic contact angle increased as H2O concentration increasing. However, the rejection of BSA and Dextran of resultant PVDF membranes changed little as H2O concentration increasing. The improved performance was attributed to the existence of non-solvent, which was solubilized by the polar head groups of Tween-80reverse micelle to form the water pool. Furthermore, the interaction between polar head of surfactant and water provided a balance resistance to the interconnection between PVDF and hydrophobic chains of the surfactant, which enhanced the thermodynamics stability of casting solution.Secondly, to obtain the target modulation path of Tween-80and H2O dopants, various compositions of coagulants and temperatures of casting solutions were utilized. PVDF membranes possessed interconnected bi-continuous structures with superior mechanical properties and fine hydrophilicity improvement were obtained from PVDF-DMAc-Tween-80-H2O system with60℃and ambient temperature casting solution, respectively. Tween-80-H2O mixtures were adopted as dope additive; water-ethanol (50:50, mass ratio) and ethanol were chosen as coagulants. The effects of process parameters in terms of variation contents of dope additives, casting solution temperatures and coagulant compositions on phase inversion process and performances of resultant PVDF membranes were investigated. Results showed that the compositions of coagulants modulated the sequence and the extent of liquid-liquid and liquid-solid demixing (crystallization), while the contents of dope additives and casting solution temperatures changed the precipitation rate of the casting solutions. During demixing process, water diffused from interior of Tween-80reverse micelles, resulting in the accelerated precipitation rate and surface segregation process of polar head groups of Tween-80. And the high temperature of casting solution contributed to the enhancing diffusion rate of liquid-liquid demixing on crystallization. The coagulant compositions changed the extent of liquid-liquid and solid-liquid demixing dynamic of casting solutions. Ethanol coagulant contributed to the crystallization of PVDF-DMAc-Tween-80-water system occurred prior to liquid-liquid demixing. This longer time-delay demixing process favored the formation of porous foliage type top-structures with fibrils or laths bi-continuous fine structure of membrane bulk, contributing to the increased flux and significant hydrophilicity improvement. While casting solutions in water-ethanol coagulant exhibited the shorter time-delay demixing process with both liquid-liquid demixing and crystallization, resulting in the formation of the fine structure in the form of the strings or stripes and limited the hydrophilic improvement. The predominant typical α and β type crystalline with crystallinity degree of59.1%in PVDF was attributed to the existence of dope additives, high temperature of casting solution and water-ethanol coagulant. This was consistent with the superior mechanical properties of corresponding PVDF membrane.In order to avoid the high activity, soluble problem of Tween-80during PVDF membrane preparation and operating process, as well better modulation configuration of PVDF membranes, P(PEGMA-r-MMA) amphiphilic copolymer with Mn of66500g/mol and Mw of34200g/mol was synthesized via free radical polymerization choosing polyethylene glycol monomethyl ether methyl methacrylate (PEGMA) and methyl methacrylate (MMA) as reaction monomers, and its chemical structure and composition were characterized. And polyvinylidene fluoride (PVDF)-P(PEGMA-r-MMA) blend membranes were fabricated from water and ethanol coagulants via simplified blend method by directly blending PVDF and P(PEGMA-r-MMA) amphiphilic copolymer solution (including the reaction mixture) to form casting solution. The formation of the supramolecular aggregates of PVDF-P(PEGMA-r-MMA) in PVDF solution containing the copolymer were confirmed by dynamic light scattering (DLS) and scanning electron microscopy (SEM). This contributed to the micro-structure adjustment of PVDF solution and resulted in its decreasing surface tension, accelerating precipitation rate and increasing viscosity with trivial strain thinning behavior. Furthermore, the effects of the variations in dopant contents and coagulant compositions on the performances of those blend membranes were investigated. All PVDF-P(PEGMA-r-MMA) blend membranes possessed narrow distribution mean effective pore size (p.), molecular weight cut off (MWCO), improved recovery water flux after filtration experiments of BSA and tuned configurations. Compared with the instantaneous demixing process in water coagulant, the delayed demixing process in ethanol favored the pore-forming and surface segregated of the polar head group of the copolymer, which induced the increasing μ, MWCO, tunable morphologies and hydrophilicity improvement.The results of simpilified blend method showed that the formation of the large-sized nanoparticulate aggregates (size:100～200nm) of PVDF-P(PEGMA-r-MMA) in the casting solution limited the function of the P(PEGMA-r-PEGMA) amphiphilic copolymer with respect to pore-forming and morphology modulation of the resultant membranes. Then the in situ free radical polymerization was creatively designed to obtain narrow distribution PVDF-P(PEGMA-r-MMA) supramolecular aggregates with small size and enhance better modulation configration of P(PEGMA-r-MMA); PVDF membranes with superior mechanical behaviors and enhanced antifouling properties was proven to be successfully fabricated. The DLS and SEM results verified the formation of supramolecular polymer-copolymer aggregates with small size (size:0-10nm). The narrow distribution of the supramolecular aggregates explained the decreasing surface tension, increasing viscosity with trivial strain thinning behavior and accelerating precipitation rate of the PVDF casting solution. The resultant PVDF membranes possessed narrowly distributed pore size and MWCO of the final filtration properties, which were attributed to the aggregates; additionally, their corresponding μ and MWCO increased, including the crystallinity of the a and β phase (largely in the β phase form) varied from56.1%to84.1%with increasing concentration of the monomers via in situ polymerization. Furthermore, in situ polymerization not only enlarged the recovery water flux after filtration experiments with BSA but also improved the hydrophilicity of both the top-surface and the bottom-surface of the PVDF membranes. Additionally, in situ polymerization modulated the configurations of PVDF membrane, varying from stripe-shaped grains to agglomerates of globule (with one of the globules bearing on the surface of another). The tunable morphologies, combined with the progressive enhanced crystallinity of the a and P phase were used to interpret the superior mechanical properties (Its break strength, elongation at break and Young’s modules were8.8MPa,343%and229MPa, respectively) of the resulting PVDF membranes.Finally, basic previous study, and choosing polytetrahydrofuran dimethacrylate ester (PTMGDA) that synthesied by our own lab with high reaction activity as reaction monomers instead of MMA, and reacted with PEGMA to synthesis P(PTMGDA-r-PEGMA) amphiphilic copolymer. PVDF hollow fiber UF membranes were prepared from the PVDF-TEP-DMAc-PTMGDA-PEGMA-PVP casting solution system after in situ polymerization. Combined with basic physical-chemical properties of the casting solution caused by the formation of PVDF-P(PTMGDA-r-PEGMA)-PVP supramoleculat aggregates, the configuration modulation, permeability, mechanical properties and antifouling BSA of resulant PVDF hollow fiber membranes were investigated. Results indicated that the round role appreared in the sponge-like cross-section of PVDF hollow fiber membranes, and the nanograins that constrcuted membrane bulk became widen and loose-packing as PVP concentration increasing. Besides, the membranes’pure water flux increased from15.7L.m-1.h-1to60.2L.m-1.h-1, and their mechanical properties and the rejection of Dextran (40K and70K) changed little. This showed that the synergy effects of PVP and the P(PTMGDA-r-PEGMA) amphiphilic copolymer formed via in situ polymerization on configration modulation and tuned performances of PVDF hollow fiber membranes. And the newly developed hydrophilicity PVDF hollow fiber membranes with superior mechanical properties and low-fouling of BSA are anticipated to be suitable not only for wastewater treatment, but also for bio-separation.更多还原