双凝固浴对膜蒸馏聚偏氟乙烯膜结构性能的影响

以聚偏氟乙烯(PVDF)、磷酸-N,N-二甲基乙酰胺为铸膜液体系,采用非溶剂相转化法,通过双凝固浴制备高性能的PVDF疏水微孔膜。采用正交实验的方法,考察凝固浴条件对PVDF膜结构和性能的影响。结果表明,双凝固浴法对膜的结构和性能有很大的影响,随着第1凝固浴中乙醇含量的增加,固液分相逐渐占据主导,促进了膜表面微纳米粗糙结构的形成,提高了膜表面的疏水性。以温度为60℃的质量分数40%乙醇作为第1凝固浴,浸泡时间20 s,温度60℃的水作为第2凝固浴所制备的PVDF膜,其直接接触膜蒸馏通量为28.3 kg/(m2·h),孔隙率为84.5%,平均孔径为1.05μm,接触角为116.8°。     

凝固浴体系对PVDF超滤膜性能与结构的影响

利用非溶剂相转化法(NIPS),以聚偏氟乙烯(PVDF)、聚乙烯基吡咯烷酮(PVP)为铸膜液,水、二甲基乙酰胺(DMAC)、PVP体系为凝固浴,制备外压中空纤维超滤膜。研究了凝固浴中DMAC和PVP含量以及凝固浴温度对膜性能和结构的影响。结果表明,凝固浴中DMAC含量的增加可以提高超滤膜的通量、断裂伸长率和表面的孔径,降低膜丝拉力;PVP含量对膜通量、拉力与断裂伸长率有非线性影响,当着PVP的质量分数大于12%时,支撑层孔径明显增加;凝固浴温度升高可以增加膜的通量,而对孔隙率、拉力和断裂伸长率则影响不大。当凝固浴中DMAC和PVP的质量分数分别为35%和12%、凝固浴温度为70℃时,可以得到性能较好得超滤膜。     

高溶剂含量第1凝固浴停留时间对PVDF膜结构和性能的影响

以聚偏氟乙烯(PVDF)、聚乙烯吡咯烷酮(PVP)、二甲基乙酰胺(DMAc)为铸膜液体系,采用高含量溶剂DMAc水溶液作为第1凝固浴,水为第2凝固浴组成的双凝固浴制备PVDF中空纤维膜.通过扫描电镜(SEM)形貌观察,纯水水通量和BSA截留率测试,探讨了第1凝固浴停留时间对PVDF-PVP中空纤维膜性能与结构的影响.结果表明,随着膜丝在高溶剂含量第1凝固浴中停留时间从0变化至10s,膜丝纯水通量在2s时下降,之后持续增加,而BSA截留率不断降低.SEM显示随停留时间延长,膜表面孔隙率增加,亚层指状孔增多,大孔孔径增大,亚层海绵结构变得疏松.在停留时间为10s时,膜水通量达315 L·m-2.h-1,BSA截留率86％,可做为制备高通量PVDF超滤膜的最佳成形条件.     

强疏水性PDMS/PVDF微孔膜的制备及其性能研究

利用非溶剂相转化法（NIPS）,通过在聚偏氟乙烯(PVDF)铸膜液中加入聚二甲基硅氧烷(PDMS),制备了PDMS/PVDF共混疏水微孔膜,并研究了凝胶浴组成（水/乙醇）对铸膜液凝胶动力学、膜形貌、疏水性及力学性能的影响。结果表明,随着凝胶浴中乙醇百分含量由零增加至100 %时,PDMS/PVDF共混膜的断面上指状孔基本消失,海绵状孔结构贯穿断面;当凝胶浴中乙醇含量为100 %时,PDMS与PVDF发生分相;膜表面疏水性能增加,水接触角达到139.68 °;弹性模量、拉伸强度、断裂伸长率分别由（48.06±4.20）、（2.82±0.15） MPa、（92.90±2.53） %下降至（15.70±2.83）、（0.72±0.13） MPa、（15.47±1.63） %。     

PEO改性PVDF/SMA膜结构和性能

将聚氧化乙烯(PEO)添加到聚偏氟乙烯/苯乙烯马来酸酐树脂(PVDF/SMA)膜体系中,通过非溶剂致相分离法(NIPS)制备了添加不同PEO含量的PVDF/SMA共混膜。其中PEO质量分数为2%的共混超滤膜性能最好,水通量为531.1L/(m²·h),牛血清蛋白(BSA)截留率为65.8%,水接触角为63.6°,膜剥离强度为0.2756kN/m。接着以PVDF/SMA膜为主要研究对象测试了凝固浴温度对共混超滤膜的纯水通量以及BSA截留率的影响,该实验的结果表明凝固浴温度的改变对膜性能没有产生明显的影响。因此,选择在常温凝固浴温度下测试不同凝固浴成分对共混膜性能的影响。探究了膜在凝固浴成分分别为N,N-二甲基乙酰胺(DMAc)(质量分数为3%、6%、9%)、氯化钠(NaCl)(0.05mol/L、0.1mol/L、0.2mol/L)和乙醇(质量分数为3%、6%、9%)时的膜性能变化,以及对各个组分得到的膜样本进行扫描电子显微镜(SEM)表征。结果表明,随着DMAc含量增加,膜表面的孔在减少,且膜皮层的厚度增加,使得膜的水通量减少而BSA截留率提高。而随着NaCl浓度...     

第2凝固浴对气-液膜接触器用PVDF膜润湿性能的影响

以聚偏氟乙烯(PVDF)为基膜材料,以乙醇为第1凝固浴,以不同N-甲基吡咯烷酮(NMP)含量的水溶液为第2凝固浴,采用双凝固浴法制备了高疏水和高透气的PVDF膜。结果表明,以水作为凝固浴时,PVDF膜的空气侧较为平整,当用双凝固浴时,PVDF膜空气侧开孔结构和无皮层结构逐渐明显,PVDF膜基底侧较为粗糙;随着NMP含量的增大,膜的接触角先增大后减小,当第2凝固浴中的NMP的质量分数为50%时,接触角、最小液体渗透压力、通气量最大,分别为141.9°、35 kPa、540 L/h。     

凝固浴温度对PVDF/PES-C共混膜结构及性能的影响

以邻苯二甲酸二丁酯(DBP)和N,N-二甲基乙酰胺(DMAc)为混合稀释剂,采用热致相分离法(TIPS)制备了聚偏氟乙烯(PVDF)/酚酞型聚醚砜(PES-C)共混膜,考察了不同凝固浴温度对膜结构和性能的影响。采用扫描电镜观察了膜的结构,测试了膜的纯水通量。运用DSC和XRD方法检测了膜的结晶性能。将制备的膜在膜生物反应器(MBR)中运行测试了膜的污水通量和出水指标。随凝固浴温度的升高,共混膜的最高熔融温度上升,膜中α晶型的含量增加。在凝固浴温度为25℃时,膜形成了较为致密的皮层结构和较为疏松的支撑层结构,此时共混膜的纯水通量和污水通量达到最大值,且MBR出水COD和NH4+-N含量达到排放要求。     

相转化法制备聚砜膜研究进展

系统概述了相转化法制备聚矾膜时聚矾含量、添加剂、凝固浴及铸膜液在空气中的蒸发时间对其结构和性能的影响。随着聚矾含量的增加,膜结构从疏松向致密转变;在铸膜液中添加适合的添加剂可制备适当结构和渗透性能的聚矾膜;在凝固浴中添加适量的溶剂,可有效抑制膜内大孔结构的形成;空气中蒸发时间的增大时,膜表面趋于疏松,当增加到一定程度后基本趋于稳定。还综述了相转化法制备聚矾膜时聚矾含量、添加剂、凝固浴及铸膜液在空气中的蒸发时间对其结构和性能的影响。     

聚偏氟乙烯中空纤维膜纺丝凝固浴中有机物含量测定方法的研究

通过紫外光谱扫描分析PVDF中空纤维膜纺丝凝固浴的主要成分,用折光指数法测定了聚偏氟乙稀(PVDF)中空纤维膜纺丝过程中凝固液主要成分N,N-二甲基乙酰胺(DMAc)随时间的变化及其与COD的关系。结果表明,紫外光度法、折光指数法、COD法都可以用于DMAc的测定,其中折光指数法对0~70%体积分数的DMAc溶液有很好的线性相关性;在纺丝过程中,凝固浴的COD与其折射率具有很好的相关性。随着凝固浴中DMAc含量升高,膜孔径和断裂强度变化不大,膜通量降低。可利用折光指数法分析监控纺丝过程中凝固浴组成。     

凝胶相转化温度和空气预蒸发时间对PVDF超滤膜性能及结构的影响

利用非溶剂相转化法(NIPS),以聚偏氟乙烯(PVDF)/聚乙烯吡咯烷酮(PVP)/N,N-二甲基乙酰胺( DMAC)为铸膜液体系,水为凝固浴制备了大通量超滤膜.考察了铸膜液温度、凝胶浴温度、空气预蒸发时间等条件对超滤膜性能与结构的影响.研究结果显示,随着铸膜液和凝胶浴温度的提高,膜纯水通量增大,强度增强,截留率降低,膜的第一泡点压力减小,膜的孔隙率随铸膜液温度升高而增大,随凝胶浴温度升高先增大后减小,膜断面指状孔发育较为通透,海绵层致密.延长铸膜液在空气预蒸发时间,膜的第一泡点压力和孔隙率降低,超滤膜截留率提高,通量和强度变化不大.     

Influence of the coagulation‐bath temperature on the phase‐separation process of poly(vinylidene fluoride)‐graft‐poly(N‐isopropylacrylamide) solutions and membrane structures

A poly(vinylidene fluoride)‐graft‐poly(N‐isopropylacrylamide) (PVDF‐g‐PNIPAAm) copolymer was synthesized, and flat‐sheet membranes were prepared via the phase‐inversion method with N,N‐dimethylformamide (DMF) as the solvent and water as the coagulation bath. The effects of the coagulation‐bath temperature on poly(vinylidene fluoride) (PVDF)/DMF/water and PVDF‐g‐PNIPAAm/DMF/water ternary systems were studied with phase diagrams. The results showed that the phase‐separation process could be due to the hydrophilicity/hydrophobicity of poly(N‐isopropylacrylamide) at low temperatures, and the phase‐separation process was attributed to crystallization at high temperatures. The structures and properties of the membranes prepared at different coagulation‐bath temperatures were researched with scanning electron microscopy, porosity measurements, and flux measurements of pure water. The PVDF‐g‐PNIPAAm membranes, prepared at different temperatures, formed fingerlike pores and showed higher water flux and porosity than PVDF membranes. In particular, a membrane prepared at 30°C had the largest fingerlike pores and greatest porosity. The water flux of a membrane prepared in a 25°C coagulation bath showed a sharp increase with the temperature increasing to about 30°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Omega-3 Polyunsaturated Fatty Acids Concentration Using Synthesized Poly-Vinylidene Fluoride (PVDF) Asymmetric Membranes

In this study, the performance of synthesized poly‐vinylidene fluoride (PVDF) membranes to concentrate ω3‐polyunsaturated fatty acids from lantern fish oil was evaluated. The PVDF membranes were prepared via the phase inversion method. The effect of coagulation bath temperatures (CBT: 0, 25 and 50 °C) on the morphology of the membranes and the ω3‐PUFA concentration process was examined and discussed. Scanning electron microscopy images showed that an increasing coagulation bath temperature (CBT) leads to a more porous structure in the membranes as well as a larger pore diameter. ω3‐PUFA concentration was evaluated at different pressures and temperatures, ranging from 3 to 5 bar and 20 to 40 °C, respectively. The PVDF membrane prepared at a CBT of 0 °C (M1) resulted in the best ω3‐PUFA concentration (40.4 %) at a pressure and temperature of 5 bar and 30 °C, respectively. Conversely, the PVDF membrane formed at CBT of 50 °C (M3) showed the highest oil flux. In addition, fouling analysis indicates that complete pore blocking was the predominant mechanism for the M1 membrane and intermediate pore blocking for the M2 and M3 membranes.     

凝固浴组成对NMMO法纤维素膜形貌的影响

为实现对分离用纤维素膜形貌的控制,采用NMMO法,分别以水、甲醇、乙醇和由它们配制的双组分溶液为凝固浴,制备了纤维素膜,观察了干膜的表面和断面形貌,测定了湿膜的孔结构参数,在对比基础上分析了干膜中微孔的形成过程与机制,探讨了纤维素结晶尺度与湿膜平均孔径的相关性和影响因素.研究表明,不同凝固浴制备出的纤维素膜在干态形貌上差别明显.纤维素膜的湿态孔隙率基本不受凝固浴组成影响,而干态下的致密区域在水溶胀后呈现多孔结构,对湿膜平均孔径影响很大.通过改变凝固浴组成,可分别或协同地调控纤维素膜的干态或湿态结构.     

Preparation and characterization of asymmetric polysulfone membrane for separation of oxygen and nitrogen gases

Defect‐free skinned asymmetric gas separation membranes were prepared by a dual bath coagulation method using a wet phase inversion technique. The membranes were cast from polysulfone solution in different solvents such as: dimethyl‐formamid, 1‐methyl‐2‐pyrrolidone, N‐N‐dimethyl‐acetamide (DMAC), and tetrahydrofuran. The mixtures of water/iso‐propanol (IPA), water/propanol, water/ethanol (EtOH), and water/methanol (MeOH) with volume ratio of 80/20 were used as the first coagulation bath. This led to the formation of a dense skin top layer. Distillated water was used as the second coagulation bath. The influences of several experimental variables, such as thickness of the membrane, polymer concentration, type of solvent and nonsolvent, immersion time in IPA 20%, and second coagulation bath temperature on skin layer and sublayer were elucidated. For preparing membrane with higher permeance, the influence of internal nonsolvents and addition of polyvinylpyrrolidone (PVP) as additive were investigated. The membrane performance was tested in terms of gas permeance and selectivity for O₂/N₂ separation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Porous poly(vinylidene fluoride) membrane with highly hydrophobic surface

The preparation of very hydrophobic poly(vinylidene fluoride) (PVDF) membranes was explored by using two methods. The first one was the modified phase inversion method using a water/N,N‐dimethylacetamide (DMAc) mixture instead of pure water as a soft precipitation bath. The second method was a precipitation‐bath free method, that is, the PVDF/DMAc casting solution underwent gelation in the open air instead of being immersed into a precipitation bath. The morphology of the surface and cross section of the membranes was investigated by using scanning electron microscopy (SEM). It was found that the membranes exhibited certain micro‐ and nanoscale hierarchical roughness on the surface, which brought about an enhanced hydrophobicity of the membrane. The contact angle (CA) of the samples obtained by the second method was as high as 150° with water. The conventional phase inversion method preparing PVDF porous membrane using pure water as precipitation bath usually results in an asymmetric membrane with a dense skin layer having a CA close to that of a smooth PVDF surface. The modified approach avoided the formation of a skin‐layer and resulted in a porous and highly hydrophobic surface of PVDF. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1358–1363, 2005     

Study on the control of pore sizes of membranes using chemical methods: Part III. The performance of carbonates and bicarbonates in the membrane-making process by the chemical reaction

In this paper, polyvinylidene fluoride (PVDF)/polymethyl acrilate (PMMA)/cellulose acetate (CA) blend UF membranes were prepared by chemical reaction introduced phase-inversion method. The results of the experiment show that: (1) The membrane pore size distribution is more uniform due to the presence of carbonates or bicarbonates in the coagulation bath; (2) No more than the stoichiometric ratio amount of carbonates or bicarbonates in the coagulation bath can effectively improve the membrane pore size distribution and make the pore size of membrane more uniform; (3) The membrane prepared by carbonates solution as a working solution in coagulation bath possess superior performance than that by bicarbonates.     

Dye removal using hydrophobic polyvinylidene fluoride hollow fibre composite membrane by vacuum membrane distillation

Hydrophobic polyvinylidene fluoride (PVDF) hollow fibre composite membranes were prepared by the dilute solution coating process to build a special surface structure that was similar to the dual micro‐nano structure on the lotus leaf. Poly(vinylidene fluoride‐co‐hexafluoropropene) was chosen as the hydrophobic polymer candidate in dilute solution. Membrane morphology and surface hydrophobicity were evaluated by scanning electron microscopy and dynamic water contact angle measurement. The prepared PVDF hollow fibre membranes were employed to separate dyes (Congo Red and Methylene Blue) from water by vacuum membrane distillation. The effects of operational conditions (feed temperature, vacuum pressure and feed flow rate) on the vacuum membrane distillation performance of different PVDF membranes were investigated. The results indicated that the water contact angle values of PVDF composite membrane surfaces improved from 93.6° to 130.8°, which was mainly attributed to the formation of micro‐nano rods. This structure was similar to the dual micro‐nano structure on the lotus leaf. Under test feed temperature, vacuum pressure and feed flow rate conditions, the dye rejection rate of Congo Red and Methylene Blue by the hydrophobic PVDF hollow fibre membrane remained above 99.5% and 99%, which was higher than that of the pristine PVDF membrane (99% and 98%, respectively). In addition, the hydrophobic PVDF hollow fibre composite membrane showed higher permeation flux under different conditions compared with the pristine PVDF membrane, which was attributed to membrane surface hydrophobicity and the electrostatic interactions between dyes and the PVDF membrane surface.     

化学浴沉积制备防污自洁型PVDF/PMMA共混膜研

使用NaOH溶液亲水改性聚偏氟乙烯(PVDF)/聚甲基丙烯酸甲酯(PMMA)共混膜,在共混膜表面化学浴沉积烷基氯硅烷,构筑微纳米结构,制备出具有超疏水能力的PVDF/PMMA共混膜,对共混膜的微观结构和性能进行了表征。结果表明,亲水改性提升了PVDF/PMMA共混膜表面烷基氯硅烷的化学浴沉积效果;亲水改性的最佳工艺条件为：NaOH的浓度为40 %、反应时间为60 min、反应温度为70 ℃;化学沉积后的PVDF/PMMA共混膜接触角高达154.6 °;集灰实验表明,倾斜角度约为1 °时水滴能将膜表面的灰尘带走,膜的防污自洁性能优良。     

High flux and CO2 stable La0.6Ca0.4Co0.2Fe0.8O3-δ hollow fiber membranes through internal coagulation bath optimization

La_0.6Ca_0.4Co_0.2Fe_0.8O_3-δ (LCCF) ceramic powder prepared by sol-gel method was used to fabricate LCCF hollow fiber (HF) membranes via a combined phase inversion-sintering technique. Three types of LCCF HF membranes were developed by changing the composition of the internal coagulation bath containing H₂O, EtOH or the mixture of NMP + EtOH. The best one was achieved via the mixture (0.7NMP + 0.3EtOH by weight). At 1000 °C, the oxygen flux reached 6.16 mL min⁻¹ cm⁻² under inert sweep gas; however, it reached 8.83 mL min⁻¹ cm⁻² when reactive CH₄ was used as the sweep gas, mirroring the high capability of oxygen transport through the membrane. The good stability of the developed LCCF membrane was confirmed by a series of long-term operation tests up to 300 h with sweep gas containing CO₂. The findings of this work can advance the applications of LCCF membranes to reactors where CO₂ atmosphere cannot be avoided.