Formation,morphology and control of high-performance biomedical polyurethane porous membranes by water micro-droplet induced phase inversion

Biomedical polyurethane (BPU) porous membranes with controlled morphology and excellent permeability and mechanical properties were prepared via a method involving a phase inversion induced by water micro-droplets, which were generated by an ultrasonic atomizer. The cross-section morphology, air permeability and mechanical properties of the porous membranes were investigated. The SEM images demonstrated that the adjacent pores were connected by a micro-hole, serving as a “backdoor” for the pore. An interconnected porous structure was obtained, improving the air permeability of the BPU membrane relative to the membrane produced by immersion precipitation. Our studies indicated that the diameter of the pores in the membrane depended on the solution viscosity, allowing porous membranes with a desired morphology to be obtained by adjusting the polymer concentration and solution viscosity. The application of micro-droplets of water during membrane preparation reduced the exchange rate between the solvent and nonsolvent, resulting in the microphase separation of polymer molecules and the formation of a uniform porous structure in the membrane, which improved the air permeability and mechanical properties of the BPU porous membranes. This is a simple and effective preparation method for high-performance porous membranes with potential applications in tissue engineering scaffolds, controlled-release drug delivery and vascular grafts.     

Fabrication of porous forsterite-spinel-periclase ceramics by transient liquid phase diffusion process for high-temperature thermal isolation

Porous forsterite-spinel-periclase ceramics with low thermal conductivity were synthesized via a transient liquid phase diffusion process by using pre-synthesized pellets and fused magnesia powder. The effects of sintering temperature on the pore formation, phase composition, sintering behavior, and properties of the resulting porous ceramics were investigated. The pre-synthesized pellets had a porous structure and contained a large amount of cordierite and enstatite. During the sintering progress, the pellets were converted into a transient liquid phase, which diffused into the solid MgO matrix. The liquid phase diffusion reaction promoted forsterite and spinel formation, which resulted in the in-situ formation of large pores. At elevated temperatures, the liquid phase disappeared and a large number of well-developed grains were simultaneously precipitated from the liquid phase. Porous ceramics with thermal conductivities of 0.42–0.48 W/(m·K) and refractoriness under load values of 1588 °C and 1624 °C were obtained after sintering at 1600 °C for 3 h.     

Studies on phase separation rate in porous polyimide membrane formation by immersion precipitation

Phase separation rate during porous membrane formation by immersion precipitation was investigated by light scattering in a polyimide/N‐Methylpyrrolidone (NMP)/water system. In the light scattering measurement, plots of scattered intensity against scattered angle showed maxima in all cases, which indicated that phase separation occurred by a spinodal decomposition (SD). Characteristic properties of the early stage of SD, such as an apparent diffusion coefficient D_app and an interphase periodic distance Λ, were obtained. The growth process of Λ was also followed by light scattering. The growth rate had the same tendency as D_app when water content in the nonsolvent bath and the polymer concentration in the cast solution were changed. The pore size of the final membrane increased with decreasing water content, which was opposite to the tendency of Λ growth rate. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 292–296, 2003     

Asymmetric porous cordierite ceramic membranes prepared by phase inversion tape casting and their desalination performance

Asymmetric porous cordierite ceramic membranes were fabricated by phase inversion tape casting method. It is shown that the membranes consist of a relatively dense skin layer on the top, a sponge layer at the bottom and a finger-like layer in the middle. The membranes have a hierarchical pore structure, where macrovoids (denoted as dozens-micron-sized (DMS) pores) are present in the finger-like layer and micron-sized (MS) pores are located in the skin layer, sponge layer and the wall of macrovoids. After surface silylation by post-grafting with 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FAS), the sample with a starting powder/polyethersulfone (PESf) weight ratio of 9 (M − 4) becomes hydrophobic, with a water contact angle of 150°. At a NaCl concentration of 3.5 wt%, a feed rate of 18L/h and a feed temperature of 80 °C, the hydrophobic M − 4 membrane exhibits a water permeate flux of 22.33 kg/m²h, which is considerably larger than that of the membranes prepared by dry pressing method previously, and a salt rejection of 99.9%. The higher water permeate flux is attributed to the much lower transport resistance of water vapor in the membranes of the present work.     

Dehydration of ethanol/water mixtures by pervaporation using soluble polyimide membranes

A series of soluble polyimides derived from 3,3′,4,4′‐benzhydrol tetracarboxylic dianhydride (BHTDA) with various diamines such as 1,4‐bis(4‐aminophenoxy)‐2‐tert‐butylbenzene (BATB), 1,4‐bis(4‐aminophenoxy)‐2,5‐di‐tert‐butylbenzene (BADTB), and 2,2′‐dimethyl‐4,4′‐ bis(4‐aminophenoxy)biphenyl (DBAPB) were investigated for pervaporation separation of ethanol/water mixtures. Diamine structure effect on the pervaporation of 90 wt% aqueous ethanol solution through the BHTDA‐based polyimide membranes was studied. The separation factor ranked in the following order: BHTDA–DBAPB > BHTDA–BATB > BHTDA–BADTB. The increase in molecular volume for the substituted group in the polymer backbone increased the permeation rate. As the feed ethanol concentration increased, the permeation rate increased, while the water concentration in the permeate decreased for all polyimide membranes. The optimum pervaporation performance was obtained by the BHTDA–DBAPB membrane with a 90 wt% aqueous ethanol solution, giving a separation factor of 141, permeation rate of 255 g m^?2 h^?1 and 36 000 pervaporation separation index (PSI) value. Copyright © 2006 Society of Chemical Industry     

Preparation of silica nanospheres and porous polymer membranes with controlled morphologies via nanophase separation

ABSTRACT: We successfully synthesized two different structures, silica nanospheres and porous polymer membranes, via nanophase separation between silica sol and polymer. Silica sol, which was in-situ polymerized from tetraorthosilicate, was used as a precursor. Subsequently, it was mixed with a polymer that was used as a matrix component. It was observed that nanophase separation occurred after the mixing of polymer with silica sol and subsequent evaporation of solvents, resulting in organizing various structures, from random network silica structures to silica spheres. In particular, silica nanospheres were produced by manipulating the mixing ratio of polymer to silica sol. The size of silica beads was gradually changed from micro- to nanoscale, depending on the polymer content. At the same time, porous polymer membranes were generated by removing the silica component with hydrofluoric acid. Furthermore, porous carbon membranes were produced by using carbon source polymer through the carbonization process.     

Preparation of porous-structured LiFePO4/C composite by vacuum sintering for lithium-ion battery

The LiFePO₄/C (LFP/C) composite as a cathode material for lithium-ion battery was synthesized by solid-state reaction under vacuum sintering condition (20–5 Pa). The effects of vacuum sintering temperature and time on the phase composition, morphological structure, and electrochemical performance of LFP/C composite were investigated by X-ray diffraction, scanning electron microscopy, galvanostatic charge–discharge cycling test, and electrochemical impedance spectroscopy. The synthetic LFP/C composite possessed uniform particle-size distribution with porous architecture upon sintering at 650 °C for 12 h and thus exhibited the highest discharge capacity and best cycle performance. The complete decomposition of citric acid at a suitable temperature under vacuum condition resulted in the formation of porous structure. Compared with atmospheric argon sintering, vacuum sintering method led to the formation of porous architecture, the porous sample showed excellent cycle performance with less than 2% capacity loss after 80 cycles at 0.2 C, and reached the discharge specific capacity of 87.6 mAh g⁻¹ at 10 C rate, these are better than that of atmospheric argon sintering. The LFP/C composite prepared under vacuum sintering also reduced the optimum sintering temperature by nearly 100 °C compared with that prepared under atmospheric argon sintering.     

Network polyimide membranes prepared by interfacial polymerization for hot H2 purification

Novel polymeric membranes are to be developed for hot H₂/CO₂ separation. In this work, network polyimide (PI) membranes are prepared via a simple interfacial polymerization method using low-cost melamine and pyromellitic dianhydride monomers. The membrane performance surpasses the upper bound of H₂/CO₂ separation. Moreover, the membranes exhibit a H₂/CO₂ separation factor of 18.7 at 623 K and a robust performance after treatment with steam and H₂S.     

叔丁醇基凝胶注模成型制备氧化铝多孔陶瓷

以微米级Al2O3粉料为原料,叔丁醇为溶剂,采用凝胶注模成型工艺制备了氧化铝多孔陶瓷,并研究了Al2O3浆料的固相体积分数(分别为8%、10%、13%和15%)对1 500℃保温2 h烧后氧化铝多孔陶瓷的气孔率、气孔孔径分布、耐压强度、热导率和显微结构的影响.结果表明:当Al2O3浆料的固相体积分数从8%增加到15%时,氧化铝多孔陶瓷烧结体的总气孔率从71.2%逐渐降低至61.2%,气孔平均孔径从1.0 μm逐渐减小至0.78 μm,耐压强度从16.0 MPa逐渐增大至45.6 MPa,而热导率从1.03 W·(m·K)-1逐渐增大至1.83W·(m·K)-1.     

Surface modification of polyimide and polysulfone membranes by ion beam for gas separation

The surface carbonization of polyimide (PI) and polysulfone (PSf) by ion beam has been performed to adapt the carbon molecular sieve properties on the skin of the polymeric membranes without the deformation of the membrane structure. In order to control the structure of membrane skin and to improve gas transport properties, the irradiation conditions, such as the dosage and the source of ion beams, have been varied. The ideal separation factor of CO₂ over N₂ through the surface‐modified PI and PSf membranes increased threefold compared to those of the untreated, pristine membranes, whereas the permeability decreased with almost two orders of magnitude. This appears to be due to the fact that the structure of membrane skin has been changed to a barrier layer. The formation of barrier layer was confirmed by comparing the calculated values of a simple resistance model with the experimental results, and the estimated permeability of this barrier was 10⁻⁴ barrer. It was concluded that ion beam irradiation could provide a useful tool for improving selectivity for gas separation membranes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1554–1560, 2000     

Formation of integrally skinned asymmetric polyetherimide nanofiltration membranes by phase inversion process

Integrally skinned asymmetric polyetherimide (PEI) membranes were prepared by the phase inversion process from casting solution containing dimethylformamide (DMF) as a solvent and 1,4‐dioxane as a cosolvent. Deionized water was used as a coagulation medium in preparing asymmetric membranes. The effect of 1,4‐dioxane was investigated by measuring casting solution properties, permeation properties, and membrane structures. Various effects of polymer concentration, evaporation time, and coagulation bath temperature were also studied. Low miscibility of 1,4‐dioxane with coagulant (water) resulted in reducing membrane pore size. The molecular weight cutoff values of asymmetric membranes could be controlled by changing the amount of 1,4‐dioxane in the casting solution. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1300–1307, 2002; DOI 10.1002/app.10452     

Superior hydrophobicity of nano-SiO2 porous thermal insulating material treated by oil-in-water microemulsion

Nano-SiO₂ porous thermal insulating material (TIM) has drawn tremendous research interests due to its advantages of low density, high porosity and low thermal conductivity. However, its long-term stability in humid environment can be severely deteriorated by the high hydrophilicity resulting from tetrahedral coordination of oxygen and capillary effect of porous structure. It is still a great challenge to cost-effectively fabricate bulk TIM with superior hydrophobicity and consequent remarkable self-cleaning capability. Herein, via an oil-in-water microemulsion treatment, we have proposed a new strategy to construct 3D superior hydrophobic nano-SiO₂ porous TIM. The polymethylhydrosiloxane-modified TIM exhibits a large water contact angle of 166°, and corresponding excellent self-cleaning characteristic while maintaining low thermal conductivity of 0.031 W/m·K. Moreover, our high hydrophobicity of TIM exhibits excellent durability under high temperature up to 400 °C, high humidity of 100%, and chemical erosions. Detailed knowledge of the physical chemistry basis of the superior hydrophobic nano-SiO₂ porous TIM can provide great opportunity to fabricate advanced self-cleaning and heat insulating devices especially targeted for harsh environments.     

超临界CO_2法制备乙酸纤维素微孔膜

以超临界CO2为非溶剂,丙酮和N, N-二甲基甲酰胺（DMF）为溶剂,制备了乙酸纤维素（CA）微孔膜,采用扫描电镜表征膜的微观形态并测定了膜的纯水通量,考察了溶剂与CO2的亲和性、CA质量分数、成膜压力、成膜温度、保压时间和卸压速度等因素对膜形态及性能的影响。实验结果表明,以丙酮为溶剂可制备出表观形态均一完整的膜;随着CA质量分数的增加,膜孔径变小,膜的水通量迅速降低;随着成膜压力、成膜温度的升高,膜水通量均先增加后减小;保压时间及卸压速度对膜水通量的影响较小。当CA质量分数为10 %时,在成膜压力为15 MPa,成膜温度为45 ˚C,保压45 min,快速卸压的操作条件下,微孔CA膜的水通量可达30 L·m-2·min-1。     

Preparation and performance of novel thermal stable composite nanofiltration membrane

The novel thermal stable composite nanofiltration membranes were prepared through the interfacial polymerization of piperazine and trimesoyl chloride on the poly (phthalazinone ether) ultrafiltration substrate. The effects of polymerization and testing conditions on membrane performance were studied. The surface morphologies of the substrate and the composite membranes were observed by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM). The separation properties of membranes for dyes and salts were tested. The composite membranes show good thermal stability. The rejection for Na2SO4 was kept over 96%, while the flux reached 400 L·m⁻²·h⁻¹ when it was tested at 1.0 MPa and 80°C. When tested at 1.0 MPa and 60°C, the rejection of the composite membrane for dyes was kept at high level, and the flux reached 180–210 L·m⁻²·h⁻¹, while the rejection for NaCl was lower than 20%. __________ Translated from the Journal of Functional Materials, 2007, 38(12): 2025–2027, 2031 [译自: 功能材料]     

Improved thermal stability and flame resistance of flexible polyimide foams by vermiculite reinforcement

In this work, a series of flexible polyimide composite foams with dianhydride and isocyanate as the starting materials were prepared by pre‐dispersing vermiculite in isocyanate. The experimental results revealed that the cellular diameter of foams obviously decreased with the addition of vermiculite. The open cell content decreased with the increase of vermiculite, and foams containing vermiculite possessed higher apparent densities of about 10 kg/m³ when compared with the neat polyimide foams. The compressive strength was dramatically enhanced by vermiculite incorporation, and reached maximum when the filler content was 2%, indicating dramatically reinforcing effect of vermiculite. With the addition of vermiculite, the thermal stability and flame resistance of polyimide foams were improved. The limiting oxygen index of polyimide foams showed an increase from 31 to 33.5% with increase of vermiculite from 0 to 8% and the peak heat release rate decreased, indicating high flame retardant properties. Vermiculites possess excellent heat insulation and high temperature stability. When conditioned at high temperature, the filler would block the heat transfer during the bulk foam. Therefore, it is feasible to further increase the mechanical and thermal properties of polyimide foams by vermiculite filling. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44828.     

含氰基聚酰亚胺薄膜的制备及其热分解动力学

以4-[3,5-双(4-氨基苯氧基)苯氧基]邻苯二甲腈和3,3′,4,4′-联苯四甲酸二酐为原料,经聚酰胺酸热酰亚胺化制备含氰基的聚酰亚胺(CN-BP-PI)薄膜。采用傅里叶变换红外光谱、热重分析、差示扫描量热法对CN-BP-PI薄膜进行了分析。采用动态热重法研究了CN-BP-PI的分解动力学,用积分法结合常见固相热分解反应动力学函数来判断热分解的动力学函数。由Ozawa,KAS,Kissinger,Achar,Coats-Redfern,MacCallum-Tanner,van Krevelen方程求热分解反应的动力学参数。转化率为0.2~0.8时所得CN-BP-PI在氮气中热分解反应的表观活化能为119.68~215.61 kJ/mol,平均活化能为136.35 kJ/mol,指前因子平均值为8.52×107 s-1。     

Understanding and guiding the phase inversion process for synthesis of solvent resistant nanofiltration membranes

Since its introduction in membrane technology in the 1960's, phase inversion by means of immersion precipitation has been widely studied for the preparation of membranes to be applied in the fields of microfiltration (MF) and ultrafiltration (UF). However, much less knowledge is available about this process in terms of integrally skinned asymmetric nanofiltration membranes, especially for more hydrophobic polymers applied in solvent resistant nanofiltration (SRNF). This review focuses on the preparation aspects of integrally skinned asymmetric membranes to be applied in the field of SRNF via phase inversion. It starts with the explanation of the basic principles of the phase inversion process, covering both thermodynamic and kinetic aspects. Further, it summarizes the parameters that significantly influence final membrane performance and morphology, including polymer type and concentration, casting solvent, additives, evaporation time, and temperature, humidity, membrane thickness, composition, and temperature of coagulation bath and post‐treatment. Literature contained within this review constitutes the core references in the field of SRNF, but also several references on preparation of MF, UF, aqueous NF, and reverse osmosis (RO) membranes have been included to better clarify or illustrate certain aspects of the process. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42130.     

Morphology and performance control of PLLA-based porous membranes by phase separation

The structure, porosity and crystallization behavior of poly (L-lactic acid) and poly (L-lactic acid)/polyurethane porous membranes, prepared from ethanol/dioxane and ethanol/water coagulation baths through immersion precipitation, have been systematically investigated. The diffusion rate between solvent and nonsolvent as well as the equilibrium phase diagram of PLLA/solvent/nonsolvent system were also well studied. It has been proved that the ultimate structure and performance of the membranes could be mediated under control by suitable adjustment on phase separation behavior of the ternary system through varying coagulation bath compositions. The results show that the presence of lower ratio of dioxane in ethanol baths endows the resulting membranes with uniform sponge-like structure, higher porosity and crystallinity due to the moderate solidification and crystallization of PLLA, while increasing the water concentration tends to have a modestly opposite effect and obtains membranes with irregular finger-like structure, lower porosity and crystallinity. Under the same coagulation baths, PLLA/PU membranes possess slightly larger pores size and porosity than pure PLLA membranes, but the presence of PU appears to have no effect on the crystallinity of PLLA.     

耐溶剂聚酰亚胺/陶瓷复合膜的制备及性能表征

采用3,3',4,4'-二苯酮四羧酸二酐(BTDA)、4,4'-二氨基二苯基甲烷(MDA)和4,4'-二氨基联苯(Bz)按一定比例共聚合成了一类新的共聚型聚酰亚胺(PI-BTDA/MDA/Bz),通过调整MDA和Bz的比例制备了4种具有不同化学结构的聚酰亚胺均质膜,测试了这些聚酰亚胺均质膜对水的接触角和在N,N-二甲基甲酰胺中的溶胀性。实验结果表明:BTDA、MDA、Bz的摩尔比为5:4:1时,所得的聚酰亚胺均质膜亲水性最好,且耐溶剂性能最优。以此比例的聚酰胺酸为铸膜液,0.2mm孔径的Al₂O₃陶瓷膜片为支撑体,制备了聚酰亚胺复合膜,并考察了进料温度和进料浓度对复合膜分离性能的影响。