Electrospinning of porous polylactic acid fibers during nonsolvent induced phase separation

In this study, porous micron‐sized fibers of polylactic acid (PLA) are fabricated via electrospinning of PLA‐dichloromethane (DCM)‐hexane systems with no post treatment involved. Several compositions from the liquid‐liquid phase separated region of the phase diagram of this ternary system are selected and their electrospinnability are investigated throughout their phase separation process before gelation. We show that under constant processing and ambient parameters, there is a phase separation shelf time for each composition wherein the viscoelasticity of the systems is optimum to produce long, uniform porous fibers. For the first time, we investigate the effect of aging time during phase separation on the morphology of the electrospun fibers using scanning electron microscopy (SEM). Based on our results, certain phase separated systems provide a range of viscosity allowing for the production of porous spherical micro beads or fibers via electrospraying and electrospinning, respectively. It is also shown that obtaining long, uniform fibers from electrospinning of highly phase separated systems, e.g., a gel, is not feasible due to the high degree of crystallinity of their polymer‐rich domains and the solid‐like yielding behavior. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44862.     

Production of porous polylactic acid monoliths via nonsolvent induced phase separation

Polylactic acid (PLA) is one of the most promising polymers for use as the matrix of a bone scaffold. In this work, porous PLA monoliths are fabricated via nonsolvent induced phase separation using dichloromethane as a solvent and hexane as a nonsolvent. The PLA-dichloromethane-hexane compositions which undergo liquid–liquid phase separation followed by gelation are shown to allow for the production of high quality foams. Solvent exchange with methanol after aging the gel is found to substantially reduce shrinkage during drying. Using this simple, versatile and template-free method we produced PLA foams with porosities as high as ∼90.8%, specific surface area up to 54.14 m²/g, crystallinity up to 62.6% and compressive modulus ranging from 1.8 to 57 MPa. Depending on ternary mixture concentration and standing temperature a range of mesoporous and combined meso/macroporous morphologies suitable for use as a bone scaffold are produced.     

Polymerization of methyl methacrylate in the presence of a nonpolar hydrocarbon solvent. I. Construction of a complete ternary phase diagram through an in situ polymerization

This article presents the ternary phase diagram for methyl methacrylate (MMA), poly(methyl methacrylate) (PMMA), and n‐hexane system at 70°C. It was constructed by both theoretical calculations and online laser light scattering (LLS) technique. In situ polymerization of MMA in a nonpolar nonsolvent carried out in a LLS cell provides a new means for the accurate detection of the cloud points of highly viscous polymer mixtures, with polymer weight fractions over 0.6. The ternary phase diagram measured in this study can be used to design the reaction conditions for the precipitation and/or dispersion polymerization in a nonpolar nonsolvent medium where polymerization kinetics as well as polymer particle morphologies are strongly affected by thermodynamic phase separation phenomena. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

相转化法聚合物/溶剂/非溶剂铸膜体系的热力学计算

计算了相转化法铸膜体系中常见的典型三元相图,分析了聚合物与溶剂之间、聚合物与非溶剂之间、溶剂与非溶剂之间的相互作用参数对聚合物/溶剂/非溶剂铸膜液体系相图的影响,以及体系温度和聚合物摩尔体积对聚合物/溶剂/非溶剂铸膜液体系相图的影响。根据溶剂-非溶剂汽液平衡数据和溶解度参数得到了溶剂-非溶剂、溶剂与聚合物以及非溶剂与聚合物之间的Flory-Huggins相互作用参数,从而获得了几种常见铸膜液体系的相图。同时,利用聚合物/溶剂/非溶剂铸膜液体系的相图数据对热力学模型的参数进行了优化,取得了与实验结果较一致的计算结果。     

Solubility and phase separation of poly(L,D‐lactide) copolymers

In this study, the solubility and precipitation properties of medical‐grade stereocopolymers were investigated. The solubility of the polymers was tested with eight different organic solvents and four nonsolvents. The solubility of poly(L,D ‐lactide) stereocopolymers was highly dependent on the L /D ratio of the copolymer. The phase‐separation ability was tested by cloud‐point titration with a solvent and a nonsolvent. The solvent was in all cases dichloromethane, and the nonsolvents were n‐hexane, methanol, ethanol, and isopropyl alcohol. The results showed that n‐hexane was the most efficient nonsolvent. Methanol and ethanol showed quite similar precipitation properties. Isopropyl alcohol was the least efficient nonsolvent of those studied. Also, the L /D ratio of the copolymer had an effect on the precipitation properties. The precipitation happened most easily when the L content was high. The molecular weight of the copolymer had only a slight effect on the phase separation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Asymmetric porous membranes formed by coagulation-induced phase separation in poly(ether sulfone)/poly(vinyl pyrrolidone)/genistein blends

Development of asymmetric channel morphology driven by coagulation-induced phase separation of genistein (G) modified poly(ether sulfone)/poly(vinyl pyrrolidone) (PES/PVP) blends has been examined in relation to their miscibility phase diagram. PES/G pairs turned out to be miscible in the amorphous state, whereas solid–liquid phase separation occurred at high genistein compositions. The solid–liquid phase diagram involving the liquidus and solidus lines were computed self-consistently in the framework of the combined free energy of Flory-Huggins for liquid–liquid phase separation and phase field free energy for crystal solidification. The ternary phase diagram of PES/PVP/G blends was subsequently established that consisted of various coexistence regions. The actual amounts of genistein incorporated in the PES/PVP membranes were determined as a function of weight percent of genistein in feed. On the basis of UV-vis spectroscopy, the extent of genistein leaching during incubation in human blood was evaluated in conjunction with the PVP leaching from the blend membrane.     

Liquid–liquid phase separation in polysulfone/polyethersulfone/N‐methyl‐2‐ pyrrolidone/water quaternary system

To construct a phase diagram of the polysulfone (PSF)/polyethersulfone (PES)/N‐methyl‐2‐pyrrolidone (NMP)/water quaternary system, cloud point measurements were carried out by a titration method. The miscible region in the PSF/PES/NMP/water quaternary system was narrow compared to the PSF/NMP/water and PES/NMP/water ternary systems. The binary interaction parameters between PSF and PES were estimated by water sorption experiments. The calculated phase diagram based on the Flory–Huggins theory fit the experimental cloud points well. In addition to the usual polymer–liquid phase separation, polymer–polymer phase separation, which resulted in a PSF‐rich phase and a PES‐rich phase, was observed with the addition of a small amount of nonsolvent. The boundary separating these two modes of phase separation could be well described and predicted from the calculated phase diagrams with the estimated binary interaction parameters of the components. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2113–2123, 1999     

Application of a Ternary Phase Diagram to the Phase Separation of Oil-in-Water Emulsions Using Isopropyl Alcohol

The oil-in-water emulsion formed during an aqueous extraction of yellow mustard seed flour was destabilized using isopropyl alcohol (IPA) in a four stage extraction process, with concurrent recovery of oil and water in separate phases. The emulsion was extracted using two different approaches: phase separation extraction (PSE) that used fresh IPA as the extraction solvent at each stage, and phase separation extraction with recycle (PSER) that reused the extracted water-rich phase, containing IPA, as the extraction solvent. Extraction processes by both approaches were modeled by the ternary liquid phase diagram of IPA, canola oil and water to characterize the extraction progress. PSER resulted in improved oil–water separation and IPA usage efficiency than PSE, but achieved only 84.0?% oil recovery, compared to 92.3?% by PSE. The ternary diagram of IPA, canola oil and water offered good approximation of the oil and water separation behavior of PSE and PSER by closely predicting the compositions of the separated phases; however, the weight ratio of the separated phases were not as closely predicted.     

Interactions in PEG/Aerosil® and PLA/Aerosil® composites described by IGC-determined Flory-Huggins χ 23 parameter

Nonsolvent Induced Phase Separation (NIPS) is among the most well-known methods for membrane fabrication in which the phase separation behavior of the polymer solution is one factor that governs the structure of the membrane ultimately obtained. In this study, phase separation behavior of the polyetherimide (PEI)-casting dope was investigated for different types of coagulants and nonsolvent additives. Cloud point data were obtained by the titration method on the ternary polyetherimide/solvent/coagulant diagram from a limited number of experiments. The whole cloud point curves were then drawn by calculation using the fitting parameters based on the linearized cloud point relation (LCP). In the first part, water, methanol, ethanol, glycerol, and acetic acid were used as the coagulants for the PEI/NMP solution. The cloud point curves obtained for the above coagulants indicated that water has the strongest coagulation power among them. In the second part, methanol, ethanol, glycerol, and acetic acid were used as nonsolvent additives to NMP in different (nonsolvent additive/NMP) mass ratios. The latter (NMP?+?nonsolvent additive) mixtures were then used as the solvents to prepare PEI/(NMP?+?nonsolvent additive) solutions. The cloud point data obtained for the above solutions using water as a coagulant indicated that the cloud point curves shift toward the polymer/solution axis as the (nonsolvent additive/NMP) mass ratio increases.

Phase investigations of fats. II. Systems containing oleic and stearic acids and an organic solvent

1. The ternary systems oleic acid-stearic acid-commercial hexane and oleic acid-stearic acid-acetone containing varying amounts of the three components have been equilibrated at 0°C., −10°C., −20°C., −30°C., and −40°C.
2. From compositional data of the liquid and solid phases in equilibrium at each isotherm, ternary phase diagrams have been constructed. From these diagrams it is possible to predict the degree of separation which can be obtained with any given mixture of oleic and stearic acids, using either acetone or commercial hexane as solvent.
3. With practical solvent ratios the phase diagrams at −20°C., −30°C., and −40°C., exhibit closed areas representing liquid phase composition. The liquid phase boundaries have been established for each isotherm investigated.
4. The intersolubilizing effect of oleic acid on stearic acid, greater in commercial hexane than in acetone, and the possible formation of mixed crystals of oleic and stearic acid have been noted.
5. Oleic acid of high purity can be obtained as one of the practical applications of these data.

     

Polylactide films formed by immersion precipitation: Effects of additives,nonsolvent, and temperature

The influence of nonsolvent, crystallinity of the polymer film, and addition of dodecane (a poor solvent for the polymer and for the nonsolvent) on the morphology of polylactides films has been investigated and was related to phase separation behavior. Both amorphous poly‐DL ‐lactide (PDLLA) and crystalline poly‐L ‐lactide (PLLA) were dissolved in dichloromethane, and subsequently films were made by immersion in nonsolvent baths. PDLLA gave dense films without any internal structure, since the structure was not solidified by crystallization or glassification. PLLA films show varying structure depending on the nonsolvent. With methanol, asymmetric morphologies were observed as a result from combined liquid‐liquid demixing and crystallization, while with water symmetric spherulitic structures were formed. As a next step, dodecane was added, which is not miscible with the nonsolvent, and we found it to have a strong influence on the morphology of the films. The PDLLA films with dodecane did not collapse: a closed cell structure was obtained. In PLLA films, dodecane speeds up phase separation and induces faster crystallization in the films, and the porosity, size of the pores, and interconnectivity increased. When the PLLA solutions were subjected to a heat pretreatment, crystallization could be postponed, which yielded a cellular structure around dodecane, which did not contain spherulites anymore. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 959–971, 2007     

聚醚砜制膜液的相分离：Ⅰ.三元体系

本文对聚醚砜在不同溶剂和不同非溶剂中所构成三元体系的相分离进行研究。采用浊点滴定法测定了在常用溶剂和非溶剂中的浊点数据，溶剂对ＰＥＳ的溶解能力，依次为：甲酰胺〈二甲基业砜〈Ｎ，Ｎ－二甲基甲酰胺〈《Ｎ，Ｎ－二甲基乙酰胺〈Ｎ－甲基吡咯烷酮；以二甲基甲酰胺为溶剂，非溶剂的沉淀能力依次为：Ｈ２Ｏ〉丙三醇〉甲醇〉乙二醇〉乙醇〉丙二醇〉丙醇，线性浊点不能较好描述三元体系的浊点关系。     

Separation of neutral lipid,free fatty acid and phospholipid classes by normal phase HPLC

Normal phase high performance liquid chromatography methods are described for the separation of neutral lipid, fatty acid and five phospholipid classes using spectrophotometric detection at 206 nm. Separations were accomplished in less than 10 min for each lipid class. A mobile phase consisting of hexane/methyltertiarybutylether/acetic acid (100∶5∶0.02) proved effective in separating cholesteryl ester and triglyceride with recoveries of 100% for radiolabeled cholesteryl oleate and 98% for radiolabeled triolein. Free fatty acid and cholesterol were separated by two different mobile phases. The first, hexane/methyltertiarybutylether/acetic acid (70∶30∶0.02) effectively separated free fatty acids and cholesterol, but did not separate cholesterol from 1,2-diglyceride. A mobile phase consisting of hexane/isopropanol/acetic acid (100∶2∶0.02) effectively separated free fatty acid, cholesterol, 1,2-diglyceride and 1,3-diglyceride. Recoveries of oleic acid and cholesterol were 100% and 97%, respectively. Five phospholipid classes were separated using methylteriarybutylether/methanol/aqueous ammonium acetate (pH 8.6) (5∶8∶2) as the mobile phase. The recoveries of phosphatidylinositol, phosphatidylethanolamine, phosphatidylcholine, sphingomyelin and lysophosphatidylcholine were each greater than 96%.     

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.     

Effects of kinetics coefficients on ternary phase separation during the wet spinning process

A new Monte Carlo diffusion model is employed to simulate the phase separation of the ternary system during wet spinning process. Our results illustrate the thermodynamics parameters are the primary factors in morphology determination during the phase separation process. Meanwhile by varying kinetic parameters different fiber structures ranging from dust-like, finger-like to sponge-like morphologies are obtained. The morphological patterns are discussed in relation to the rate of particle exchange and the phase diagram. On the basis of the systematical simulation experiments we propose how the competition between segment–solvent and solvent–nonsolvent exchange determines the ultimate fiber morphologies in spinning solution.© 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Phase separation phenomena in solutions of polysulfone in mixtures of a solvent and a nonsolvent: relationship with membrane formation

The phase separation phenomena in ternary solutions of polysulfone (PSf) in mixtures of a solvent and a nonsolvent (N,N-dimethylacetamide (DMAc) and water, in most cases) are investigated. The liquid-liquid demixing gap is determined and it is shown that its location in the ternary phase diagram is mainly determined by the PSf-nonsolvent interaction parameter. The critical point in the PSf/DMAc/water system lies at a high polymer concentration of about 8% by weight. Calorimetric measurements with very concentrated PSf/DMAc/water solutions (prepared through liquid-liquid demixing, polymer concentration of the polymer-rich phase up to 60%) showed no heat effects in the temperature range of ?20°C to 50°C. It is suggested that gelation in PSf systems is completely amorphous. The results are incorporated into a discussion of the formation of polysulfone membranes.     

Formation of a bicontinuous structure membrane of polyvinylidene fluoride in diphenyl ketone diluent via thermally induced phase separation

The polyvinylidene fluoride (PVDF)‐diphenyl ketone (DPK) mixture was studied as a new system to prepare PVDF membranes via thermally induced phase separation (TIPS). The phenomena of liquid–liquid phase separation was found in this mixture when the temperature of mixture was decreasing and the PVDF concentration was less than 30 wt %. Using DPK as diluent, PVDF membrane with bicontinuous structure was obtained without necessity to add a nonsolvent or a stretching process further. The phase diagram of PVDF‐DPK system was also constructed to help investigate the effect of PVDF concentration and coarsening temperature on morphology of resulting membrane. The experiments showed that high coarsening temperatures and low PVDF concentrations resulted in the formation of the large pore size membrane. The strength of the wet membrane was decreasing with decreasing PVDF concentration. On condition that the PVDF concentration was larger than 30 wt %, thermally induced solid–liquid separation occurred and bicontinuous structure disappeared. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermally induced phase separation in liquid crystalline polymer/polycarbonate blends

Thermally induced phase separation in liquid crystalline polymer (LCP)/polycarbonate (PC) blends was investigated in this study. The LCP used is a main‐chain type copolyester comprised of p‐hydroxybenoic acid and 6‐hydroxy‐2‐naphthoic acid. Specimens for microscopic observation were prepared by melt blending. The specimens were heated to a preselected temperature, at which they were held for isothermal phase separation. The preselected temperatures used in this study were 265, 290, and 300°C. The LCP contents used were 10, 20, and 50 wt %. These parameters corresponded to different positions on the phase diagram of the blends. The development of the phase‐separated morphology in the blends was monitored in real time and space. It was observed that an initial rapid phase separation was followed by the coarsening of the dispersed domains. The blends developed into various types of phase‐separated morphology, depending on the concentration and temperature at which phase separation occurred. The following coarsening mechanisms of the phase‐separated domains were observed in the late stages of the phase separation in these blends: (i) diffusion and coalescence of the LCP‐rich droplets; (ii) vanishing of the PC‐rich domains following the evaporation‐condensation mechanism; and (iii) breakage and shrinkage of the LCP‐rich domains. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Gradient separation of soybean phospholipids with retention factors of a new polynomial correlation

The separation mechanism of solutes under gradient conditions has been studied. The separation of a mixture of soybean phospholipids (phosphatidylethanolamine, phosphatidyl-inositol, and phosphatidylcholine) in the ternary mobile phase of methanol, hexane, and isopropanol was investigated. An analytical expression was obtained to calculate the retention volume under a two step-gradient mode. The following new polynomial equation was also presented, log k′=A+BxF+CxF²+DxG+ExG² where A, B, C, D, and E are empirical coefficients and F and G are volume percentage of isopropanol and methanol in the mobile phase based on hexane, respectively. The resulting equations of the three phospholipids were used to describe the effect of the composition of the ternary mobile phase on the retention factor under step-gradient conditions.     

三元铁基离子液体-乙醇-水体系的湿法烟气脱硫性能研究(英文)

Fe-based ionic liquid(Fe-IL) was synthesized by mixing FeCl3?6H2O and 1-butyl-3-methylimidazolium chloride [Bmim]Cl in this paper.The phase diagram of a ternary Fe-IL,ethanol and water system was investigated to construct a ternary desulfurization solution for wet flue gas desulfurization.The effects of flow rate and concen-tration of SO2,reaction temperature,pH and Fe-IL fraction in aqueous desulfurization solution on the desulfuriza-tion efficiency were investigated.The results shows that the best composition of ternary desulfurization solution of Fe-IL,ethanol and water is 1︰1.5︰3 by volume ratio,and pH should be controlled at 2.0.Under such conditions,a desulfurization rate greater than 90% could be obtained.The product of sulfuric acid had inhibition effect on the wet desulfurization process.With applying this new ternary desulfurization solution,not only the catalyst Fe-IL can be recycled and reused,but also the product sulfuric acid can be separated directly from the ternary desulfurization system.