溶液预凝胶化对再生纤维素水凝胶膜性能的影响

研究了溶液预凝胶化对纤维素/NaOH/尿素水溶液体系以浸没沉淀相转化法制备的再生纤维素水凝胶膜的影响.通过静态拉伸、扫描电子显微镜研究了预凝胶化温度、凝固浴温度、凝固浴组成对再生纤维素水凝胶膜结构和性能的影响.结果表明,与常规的浸没沉淀相转化法相比,使溶液预凝胶化可以提高所制备的水凝胶膜的机械性能.经60℃预凝胶30 min后制备的水凝胶膜,拉伸强度比未经预凝胶处理的水凝胶膜提高85%.凝固浴温度的升高和凝固浴中硫酸浓度的增大均会导致形成具有较大孔结构的纤维素水凝胶膜,机械性能也随之下降.     

细菌纤维素膜的制备与性能

以细菌纤维素为原料,氯化锂(LiCl)/二甲基乙酰胺(DMAc)为溶剂,通过相转化法制备了细菌纤维素膜.用单纤维强力仪对膜的拉伸强度和伸长率进行测试,分析了细菌纤维素浓度、凝固浴温度、凝固浴浓度、凝固时间及塑化条件对膜力学性能的影响.结果表明:在一定范围内,随着制膜液中细菌纤维素浓度的增加、凝固浴温度的降低和凝固浴浓度的增大,膜的拉伸强度和伸长率均提高;随着甘油浓度的增大和塑化时间的延长,膜的拉伸强度逐渐减小,伸长率逐渐增大.     

凝固条件对α-纤维素中空纤维膜结构和性能的影响

考察了芯液种类[水、N-甲基吗啉-N-氧化物(NMMO)和二甲基亚砜(DMSO)],外凝固浴中DMSO浓度(0-60%)和外凝固浴温度(20-80℃)对纤维素中空纤维膜性能的影响,并采用扫描电镜对其结构进行了表征.结果表明,采用DMSO作为芯液,可以得到内皮层多孔的非对称结构膜;随着外凝固浴温度从20增大到80℃,外皮层的厚度逐渐减小,膜的纯水通量增大了2倍左右,而牛血清蛋白(BSA)截留率为60%左右,没有显著的变化.     

内凝固浴组成对聚醚酰亚胺中空纤维膜结构和性能的影响

以N,N-二甲基乙酰胺(DMAc)为溶剂,水为外凝固浴,乙醇为内凝固浴,DMAc为内凝固浴添加剂,采用相转化法制备了聚醚酰亚胺(PEI)中空纤维膜,研究了内凝固浴组成和纺丝液浓度对膜结构和性能的影响。实验结果表明,随着内凝固浴中DMAc含量在一定范围内增加,纤维断面指状孔有所减少,内表面由无孔到有微孔出现,但膜的水通量下降,截留率不受影响;随着纺丝液浓度提高,膜的水通量下降,截留率提高。     

内凝固浴流速对聚醚酰亚胺中空纤维膜结构与性能的影响

以N,N-二甲基乙酰胺为溶剂,水为内、外凝固浴,制备聚醚酰亚胺中空纤维膜,研究了内凝固浴流速对膜的形态结构、分离性能以及力学性能的影响。实验结果表明：随着内凝固浴流速的提高,纤维外径略有下降、内径有较大程度的提高、壁厚减小,其它结构无明显变化。与此相对应,膜的力学性能有一定程度的下降,而水通量有很大程度的提高,截留率变化不大。当内凝固浴流速／纺丝液流速大于0．4时,纤维内壁表面产生较大的轴向应力,把处于相分离早期的分子链或分相微区拉开,产生了微孔。     

纤维素膜的制备及性能研究北大核心CSCD

采用新型纤维素溶解体系NaOH/硫脲/尿素体系作为溶剂,对纤维素进行溶解、过滤、脱泡,得到澄清的纤维素溶液,然后通过H2SO4、HOAC(CH3COOH)、H2SO4/Na2SO4等不同的凝固浴制备出纤维素膜,采用XRD、SEM和强力拉伸测试等方法对纤维素膜进行表征得出纤维素膜的最佳凝固温度为20℃,不同凝固浴的最佳浓度及凝固时间分别是H2SO4-5%-3min,HOAC-9%-3min,H2SO4/Na2SO4-7%/9%-5min。其中,最佳的凝固浴及其凝固条件为20℃,H2SO4/Na2SO4-7%/9%-5min。此时纤维素膜具有均匀致密的孔洞结构,其拉伸强度及断裂伸长率分别为166.2MPa-13.5%。     

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.     

抗油污染α-纤维素中空纤维超滤膜油-水分离性能的研究

以α-纤维素为原料,一水合N-甲基吗琳-N-氧化物(NMMO.H2O)为溶剂,聚乙二醇(PEG400)为添加剂,去离子水为内外凝胶浴,采用浸入相转化法制备用于油水分离的中空纤维非对称超滤膜,并采用纯水通量表征了膜的性能.用纤维素中空纤维超滤膜进行油水分离实验,油水乳液的截留率可达到99%以上,渗透液含油量小于10 mg/L,达到国家环境保护排放要求.考察了物理清洗、物理清洗加0.1 mol/L HCL清洗、物理清洗加0.1 mol/L NaOH清洗3种清洗方法对油水污染后膜的清洗效果.其中,物理清洗加0.1 mol/LNaOH清洗的清洗方法的通量恢复率达到99%.与其它种类的膜相比,α-纤维素中空纤维膜的油水通量衰减率仅为9.5%,表现出优异的抗油污染性能.     

凝固浴温度对PVDF-g-PNIPAAm温度敏感膜成膜过程与性能的影响

通过自由基共聚的方法制备了聚偏氟乙烯-g-聚(N-异丙基丙烯酰胺)(PVDF-g-PNIPAAm)共聚物,采用浸没沉淀相转化法制备了PVDF-g-PNIPAAm共聚膜.采用超声时域反射法研究了不同凝固浴温度下PVDF-g-PNIPAAm的成膜动力学,并研究了凝固浴温度对膜结构与性能的影响.结果表明,在不同凝固浴温度下,...     

埃洛石-聚醚砜复合膜的形态结构及性能

通过非溶剂致相分离法成功制备了多孔性埃洛石一聚醚砜复合膜。通过扫描电镜观察了膜的微观结构，并对膜的水通量、截留率、亲水性和力学性能等进行了研究。结果表明：埃洛石的加入使得非对称性膜由海绵状结构转变为大指状孔结构。当凝固浴温度为40℃时，复合膜的水通量均比原膜的低。当埃洛石的质量分数为2％时，复合膜的水通量随着凝固浴温度的升高而升高。当埃洛石的质量分数从2％增加到8％时，复合膜的截留率和亲水性随之增加，力学性能随之降低。     

Effect of the preparation conditions on the formation of asymmetric poly(vinylidene fluoride) hollow fibre membranes with a dense skin

Integrally skinned asymmetric poly(vinylidene fluoride) hollow fibre membranes were prepared and characterized. The effects of phase inversion methods (dry-wet or wet) and spinning conditions, such as the type of solvent (NMP, DMAc), the concentration of polymer in dope solution, temperature of the external coagulation bath and the composition of the inner coagulant on the morphology and on the formation of a dense skin layer were investigated. The structure of the membranes was analyzed by scanning electron microscopy and the gas permeation properties with six different gases (He, H₂, N₂, O₂, CH₄ and CO₂) were measured at 25 °C to confirm the integrity of the selective skin layer. Under the proper conditions highly selective and permeable PVDF hollow fibre membranes were thus obtained by dry-wet spinning of a 30 wt.% PVDF solution in DMAc, using hot water (50 °C) as the external coagulant and a bore fluid of pure water as the internal coagulant. The best membrane had a selective outer skin with an effective thickness of approximately 0.2 μm. The ideal selectivity of the hollow fibres approached or even exceeded the intrinsic ideal selectivity of a dense PVDF film, for instance the selectivity for He over N₂ was 86.2 for the hollow fibre, whereas it was 83.5 for a dense PVDF reference film. DSC and FT-IR/ATR analysis indicated a higher fraction of the β-crystal phase in the selective skin and a high overall crystallinity than in the melt-processed film. The latter explains the relatively high selectivity and low permeability of the membranes. Intrinsic polymer properties make the membranes also suitable for vapour transport than for gas separation.     

纤维素中空纤维膜气体加湿性能的研究

采用纤维素N甲基吗啉N氧化物(NMMO)水三元纺丝体系,以去离子水为芯液,自来水为凝胶浴,湿法纺制了纤维素中空膜.经自然干燥后该膜的轴向、径向都明显收缩,断面呈现均质致密结构.干膜在水中会明显溶胀,重新润湿后具有气密性.考察了加湿水温、水气压力差等因素对膜的水渗透通量的影响,并初步测试了膜对质子交换膜燃料电池(PEMFC)反应气体H2和O2的加湿性能.实验结果表明该膜透水性能较优,气体加湿效果明显,具有应用于PEMFC反应气体加湿系统的潜力.     

Effect of take-up speed on physical properties and permeation performance of cellulose acetate hollow fibers

Cellulose acetate (CA) ultrafiltration hollow fibers were spun via the dry-jet wet spinning technique. The effect of the take-up speed on the mechanical properties, morphology, thermal properties, pure water permeation, retention, and surface characterization of hollow fiber membranes were investigated. Both the inner and outer diameters of the hollow fiber decreased with the increase of take-up speed. Macrovoids were observed on the inner surface of the drawn hollow fibers. The d-space decreased with the increase of the take-up speed. The ultimate tensile stress (UTS) increased and the breaking elongation decreased with the increase of take-up speed. The permeation performance was measured. The hydraulic permeability increased and the retention decreased slightly with the increase of the take-up speed. The surface roughness increased with the increase of the take-up speed. The thermal analysis results showed that the endothermic peak shifts to the higher temperature region and coefficient of thermal expansion (CTE) decrease for a higher take-up speed.     

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.     

Influence of drying method on morphology and properties of asymmetric cellulose hollow fiber membrane

Using a dry/wet spinning process, asymmetric cellulose hollow fiber membranes (CHFM) were prepared from a dope composed of cellulose/N-methylmorpholine-N-oxide/water. The formation mechanism for the finger-like macrovoids at the inner portion of as-spun fibers was explained. Naturally drying and three solvent exchange drying methods were tried to investigate their influence on morphology and properties of CHFM. It was found that the ethanol–hexane exchange drying was an appropriate method to minimize morphology change of the as-spun CHFM, whereas the naturally drying caused the greatest shrinkage of the fibers that made the porous membrane become dense. As a result, CHFM from ethanol–hexane exchange drying performed the highest gas permeation rate but gas permeation of the naturally dried membrane could not be detectable. The resultant CHFM from the ethanol–hexane exchange drying also showed acceptable mechanical properties, thus it was proposed to be an appropriate method for gas separation purpose. The experimental results supported the proposed drying mechanism of CHFM. The free water would evaporate or be replaced by a solvent that subsequently would evaporate but the bonded water would remain in the membrane. What dominated the changes of membrane morphology during drying should be the molecular affinities of cellulose–water, water–solvent and solvent–solvent.     

Matrimid®5218/PSf双层非对称中空纤维膜的制备及其气体分离性能研究

以商业化聚酰亚胺Matrimid®5218作为功能层材料, 聚砜作为支撑层材料, 采用共挤出法制备双层非对称中空纤维气体分离膜. 所制备的双层非对称中空纤维膜具有致密无缺陷的超薄皮层, 致密皮层厚度约为0.21 μm. 在25 ℃, 0.5 MPa下, CO2/CH4的选择性系数达51.39, CO2的渗透系数为46.29 GPU, O2/N2的选择性系数达到7.13, O2的渗透速率为6.38 GPU. 考察了温度和压力对膜的渗透系数和选择性系数的影响, 并考察了物理老化对膜性能的影响.     

A rapid feedback characterization technique for polymeric hollow fiber membranes using disperse dyes

The long time lag between fiber spinning and the availability of characteristic data for process evaluation currently complicates research in hollow fiber membrane formation. This lag time is due to the down-stream processing required before traditional gas based permeation measurements can be made on the spun fiber. A rapid feedback characterization technique, based on commercially available disperse dyes, is described here for polymeric hollow fiber membrane spinning applications. This technique involves dyeing wet hollow fibers, immediately after spinning, in an aqueous dye bath. In the present work, polysulfone fibers are shown to be characterizable using this method before lengthy down-stream processing (i.e. solvent exchange, drying, and post-treatment). Dye uptake in the hollow fibers is a function of skin porosity, thereby allowing quick evaluation of permeation characteristics. Dye uptake was measured using UV-visible spectrophotometry. Examples of fibers characterized using this technique and relationships between dye uptake and post-treated permselectivity are shown and discussed.     

Preparation and characterization of inorganic hollow fiber membranes

Inorganic hollow fiber membranes were prepared by spinning a polymer solution containing suspended aluminum oxide (Al₂O₃) powders to a hollow fiber precursor, which is then sintered at elevated temperatures. In spinning these hollow fiber precursors, polyethersulfone (PESf), N-methyl-2-pyrrolidone (NMP), and polyvinyl pyrrolidone (PVP) were used as a polymer binder, a solvent, and an additive, respectively. The inorganic hollow fiber membranes prepared were characterized using scanning electron microscope (SEM), gas permeation techniques Coulter porometer, and gravimetric analysis. Some primary factors affecting the structure and performance of the membranes such as the sintering temperature and the ratio of the aluminum oxide to the PESf polymer binder were studied extensively. The prepared inorganic membranes show an asymmetric structure, which is similar to the conventional polymeric membranes prepared from the same phase-inversion technique. The inorganic hollow fiber membrane with a higher porosity and better mechanical strength could be prepared by blending the spinning solution with a smaller amount of aluminum oxide powder.     

Effect of coagulant temperature and composition on surface morphology and mass transfer properties of cellulose acetate hollow fiber membranes

Cellulose acetate (CA) hollow fibers were spun via the dry‐jet wet spinning technique under various external coagulant compositions and temperatures. The surface morphology of the resulting hollow fiber was examined using field emission scanning electron microscopy (FESEM) and tapping mode atomic force microscopy (TMAFM). The pure water permeability (PWP) and the retention of dextran of the hollow fiber were also measured. The results showed that both the temperature and composition can affect greatly the surface morphology and hence the permeation performance of hollow fiber membranes when the temperature was over 55°C and the dimethyl formamide (DMF) content was higher than 15%. The on‐line draw ratio increased with the coagulant temperature and DMF content (in the range of 0 to 10%) in the external coagulant. The ultimate tensile strength also increased when the fibers were coagulated in 5–10% DMF and at 70°C. The PWP increased with the DMF content in the coagulant and the coagulant temperature. The retention of dextran decreased with the increase of the DMF content in the coagulant and the coagulant temperature. Copyright © 2005 John Wiley & Sons, Ltd.     

MORPHOLOGIES AND GAS SEPARATION PROPERTIES OF MELT-SPUN ASYMMETRIC POLY(4-METHYL-1-PENTENE)HOLLOW FIBER MEMBRANES*

Poly(4-methyl-1-pentene) (PMP) hollow fiber membranes were prepared by the melt-spun and cold-stretch(MSCS) method. Scanning electronic microscopy (SEM) was used to characterize the section and surface structures of themembranes with special asymmetric structure. The preliminary results of gas permeation measurements indicated that the resultant hollow fiber membranes have the potential ability for oxygen/nitrogen separation.