Effect of coagulation temperature on the properties of poly(acrylonitrile- itaconic acid) fibers in wet spinning

A dimethyl sulfoxide (DMSO)-water system was used as the coagulation bath in the wet-spun process for poly(acrylonitrile-itaconic acid) fibers. The coagulation bath concentration of DMSO was kept constant at 65%, and the jet stretch ratio was 1. The coagulation bath temperature was varied from 40 to 70 °C. The properties of the fibers so obtained were investigated. The diffusion coefficient of solvent was calculated and the concentration profiles of solvent in a moving filament were computed by using a MOL (method of lines) method. The nascent fibers coagulated at 50 °C obtained a circular symmetrical cross section with high density and strength. The diffusion coefficients of solvent (DMSO) increase with the bath temperature increase. Simulation results show that the noncircular cross section form was the response of the rapid diffusion rate and the loose structure in the core of nascent fibers was caused by the overmuch remained solvent.     

聚丙烯腈基碳纤维原丝在干湿法纺丝中非溶剂扩散过程的研究

聚丙烯腈基碳纤维具有高强度、高模量、耐高温、耐腐蚀的优良性能,广泛应用于化工、机械、造船等方面。在聚丙烯腈基碳纤维的干湿法纺丝中,纺丝原液进入凝固浴后发生的非溶剂扩散过程对聚丙烯腈基碳纤维原丝的结构和性能有重要影响。该文通过Fick定律建立了适用于纺丝原液是溶剂、高聚物和非溶剂三组分体系的非溶剂扩散数学模型,指出该模型的适用范围。此外,该文还作出了非溶剂分子的浓度随时间的变化曲线。     

Diffusion dynamics of ionic liquids during the coagulation of solution spinning for acrylic fibers

The coagulation dynamics of acrylic polymer (PAN) with 1‐butyl‐3‐methylimidazolium chloride [BMIM]Cl as solvent for PAN and H₂O as nonsolvent was investigated in detail. On the basis of Fick's second law of diffusion, a mass‐transfer model of [BMIM]Cl from concentrated PAN/[BMIM]Cl solution was established as verified with the experimental data. The established model has a good fit with the experimental data and the diffusion coefficient D of [BMIM]Cl was calculated according to the model. The diffusion coefficient D decreased a little when the concentration of solution increased. As increasing the coagulation bath concentration, the diffusion coefficient D initially increased and then decreased, reaching a maximum of 5 wt% in the coagulation bath. The diffusion coefficient D decreased with the coagulation bath temperature. From the diffusion coefficient and the structure of the coagulated filament, it can be concluded that the diffusion rate of [BMIM]Cl from PAN concentrate solutions is relatively slow, which is prospective to prepare uniform‐structure fibers. POLYM. ENG. SCI., 48:184–190, 2008. © 2007 Society of Plastics Engineers     

聚硅酸铁(PSF)混凝剂搅拌动力学的特性及理论分析

以水玻璃、硫酸亚铁及氯酸钠为原料，制备聚硅酸铁（PSF）混凝剂；用透射电镜观察PSF的微观形态，针对模拟水及松花江水，采用正交实验从GT值来研究搅拌条件对PSF混凝效果的影响。结果表明，PSF是由许多链节样物种连接而成的分维数很大的敞开式枝状结构，并且形态大小不均，覆盖范围很宽。对于不同的水质，PSF的最佳搅拌动力学条件基本一致，快搅200r／min，2min，慢搅梯度为：60r／min，3min，40r／min，5min，20r／min，2min；快搅和慢搅要密切配合，才能达到最佳的混凝效果；快搅GT值是决定混凝平衡、絮体破碎的关键因素，同时要求适度的快搅速度、稍长的快搅时间，并且要求初始速度较快的慢搅时间较长。     

Characterization of asymmetric hollow fibre membranes with graded-density skins

Asymmetric hollow fibre membranes can be prepared from polysulphone, polyethersulphone, and polyphenylsulphone by phase inversion from Lewis acid:base complex solvent systems. Formation of a complex from the non-solvent (Lewis acid) and the solvent (Lewis base) permits higher concentrations of non-solvent to be included in the spinning dope than can be added with traditional solvent/non-solvent mixtures. These membranes exhibit gas permeation rates which are a multiple of those obtained with membranes fabricated from traditional solvent/non-solvent mixtures as well as maintenance of selectivity. This enhancement in permeation performance results primarily from the creation of a skin structure with a much thinner effective separating layer than can be obtained from spinning processes utilizing solvent/non-solvent mixtures. However, it is also believed that these membranes possess enhanced free volume which is derived from the kinetics of the sol-to-gel transition. The rapid dissociation of the Lewis acid:base complex by contact with water accelerates the coagulation process, which limits conformational rearrangement. The dissociation of the Lewis acid:base complex into smaller moieties facilitates their removal from the nascent hollow fibre membranes. The acceleration of the coagulation process increases the free volume in the resultant membrane, which is reflected by an increase in the glass transition temperature that disappears upon annealing. This increase is readily seen during the first heat in a DSC scan, and it is believed that this increase is not a result of superheating, which yields the ‘T_g overshoot’ commonly observed in glassy polymers annealed below their glass transition temperatures.     

Effect of surfactant on morphology and pore size of polysulfone membrane

The skin layer structure can be changed by adjusting the diffusion rate of the non-solvent into the polymer solution between membrane and coagulation bath through adding surfactant into either coagulation bath or dope solution. When adding SDS in coagulation bath, the variation trend of apparent diffusion coefficient during phase separation and scanning electron microscopy morphology of resultant membranes indicated that, at the beginning SDS migrated to the membrane-bath interface during phase separation process, playing a role as mechanical barrier within 0.15 wt% SDS concentration. Once the SDS concentration exceeds CMC, the remaining SDS will form micelles act as a carrier, hence, the phase separation rate accelerated. The membranes were characterized roughness parameters, obtained by the atomic force microscopic technique. While adding surfactant in the dope solution, compared with SDS addition into the coagulation bath, apparent diffusion coefficient and SEM morphology showed the similar trend, and the excellent range of SDS concentration is 0.08 wt%-0.1 wt%. As changing the nature of surfactant in the dope solution, we found that, with the increase of surfactant hydrophile-lipophile balance (HLB) value, the rate of phase separation speeds up, the size of macrovoid increases, flux increases gradually and rejection is weakened.     

Compositional Effects on Structure and Transport Properties in a Polyelectrolyte Gel

The copolymerization of lithium 2‐acrylamido‐2‐methyl‐1‐propane sulfonate (LiAMPS) with N,N ′‐dimethylacrylamide has yielded polyelectrolyte systems which can be gelled with an ethylene carbonate/N ′,N ′‐dimethylacetamide solvent mixture and show high ionic conductivities. ⁷Li linewidth and relaxation times as well as ¹H NMR diffusion coefficients have been used to investigate the effect of copolymer composition as well as copolymer concentration in the gel electrolyte with respect to ionic transport and polyelectrolyte structure. It appears that ion association is likely even in the case of low lithium salt concentration; however a rapid exchange exists between the associated and non‐associated lithium species. Beyond 0.2 M of LiAMPS, both the conductivity and solvent diffusion reach a plateau, whilst lithium ion linewidth and spin‐spin relaxation are suggestive, on average, of a less mobile species. The thermal analysis data is also supportive of this association effectively leading to a form of phase separation on the nanoscale, which gives a lower overall activity of lithium ions in the solvent rich regions beyond about 0.2 M of LiAMPS, thereby leading to an increase in the final liquidus temperature of the binary liquid solvent from –9 to +5°C.     

Effects of genistein modification on miscibility and hydrogen bonding interactions in poly(amide)/poly(vinyl pyrrolidone) blends and membrane morphology development during coagulation

Miscibility characteristics of poly(amide):poly(vinyl pyrrolidone) (PA:PVP) blends containing a soybean-derived phytochemical called “genistein” have been investigated using differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The occurrence of hydrogen bonding in the binary PA/genistein (PA/G) and PVP/genistein (PVP/G) pairs as well as their ternary blends has been confirmed by Fourier transformed infrared spectroscopy (FTIR). On the basis of DSC and POM data, the morphology phase diagram of PA:PVP/G blends is mapped out, which consisted of various coexistence regions such as isotropic, liquid + liquid, liquid + crystal, liquid + liquid + crystal, and solid crystal regions. Subsequently, PA:PVP membranes modified with genistein were prepared by coagulation via solvent (dimethyl sulfoxide, DMSO) and non-solvent (water) exchange. Addition of genistein reduced the miscibility gap of the PA/DMSO/water system. The actual amounts of genistein in the final membranes have been quantified as a function of the genistein in feed. Of particular interest is the development of the gradient cross-sectional porous channels, showing the progressively larger diameters from the surface to the bottom substrate with the progression of solvent/non-solvent exchange or solvent power. Scanning electron microscopy (SEM) investigation of the morphologies of the modified membranes revealed that genistein crystals were embedded on the membrane surface as well as in the cross-section even at a very low feed concentration of genistein. A schematic of a coagulation pathway was inscribed inside a prism phase diagram in order to comprehensively illustrate the formation of genistein modified PA:PVP membranes through the solvent/non-solvent exchange process followed by drying.     

Hydrodynamic resistance in wet forming of chemical fibers

A moving model fiber of diameter 0.2-1.0 mm is used to study boundary layer formation as a function of distance, velocity of motion, and diameter of the fiber. An equation is obtained that describes the dependence of the boundary layer thickness on the viscosity, distance, radius, and velocity of motion of the fiber. In forming a complex filament, the boundary layers of adjacent filaments merge at a distance of ∼0.15 mm from the spinneret, so that the coagulation bath is immobilized (trapped) by the moving fiber and moves along with the filament at a velocity equal to 85% of the velocity of the filament. The amount of the coagulation bath drawn off from the spinneret in the form of boundary layers is equal to the product of the area of the perforated part of the spinneret times the velocity (0.85%) of the filament. This amount of the bath approaches the perforated surface of the spinneret in the form of a normal flow at a distance of ∼5 mm from the spinneret. It causes significant stress in the individual filament (jet of spin dope) and may cause the filament to break.     

Experimental study of diffusivity of hexane in bitumen-saturated porous media under high temperature/pressure conditions

Solvent mass transfer plays a key role in a thermal gravity drainage process involving solvent. The diffusion coefficients of solvent in such a process are not well studied. This article presents the effective diffusion coefficients of solvent in bitumen-saturated sands under high temperature/pressure conditions measured using a CT scanning technique. Experimental results show that the effective diffusion coefficient of n-hexane in bitumen-saturated sands varied with the solvent concentration or with the viscosity of solvent–bitumen mixture (i.e., D_e ∝ c^0.4 or D_e ∝ μ_m^−0.46). The solvent concentration weighted diffusion coefficient of n-hexane in the bitumen under the condition 160–170°C/1,900 kPa had an order of magnitude of about 10⁻⁵ cm²/s for solvent volume concentration less than 0.2. The penetration distance of n-hexane in bitumen-saturated sands depended on the nonlinearity of diffusion and had a value of −2 cm after 1-day diffusion. The stronger the nonlinearity of diffusion, the shorter the penetration distance.     

Processing and microstructural characterization of porous biocompatible protein polymer thin films

The process of electrostatic fiber formation, or electrospinning, was used to create biocompatible thin films for use in implantable devices. The morphology of the thin films was found to depend on process parameters including solution concentration, applied electric field strength, deposition distance, and deposition time. The microstructure of the coatings was examined by Transmission Electron Microscopy (TEM) and Wide-Angle X-ray Scattering (WAXS), with electrospun filaments being weakly oriented along the fiber axis. A shish kebab model for the filament morphology was proposed. The electrospinning process was shown to be a means of creating porous thin films with structural gradients and controlled morphology that could enhance biocompatibility.     

Thermodynamic study of non-solvent/dimethyl sulfoxide/polyacrylonitrile ternary systems: effects of the non-solvent species

In order to investigate the effects of the non-solvent species on the formation mechanism of polyacrylonitrile (PAN) fiber in wet spinning, theoretical ternary phase diagrams of water/DMSO/PAN and ethanol/DMSO/PAN systems were constructed based on the extended Flory–Huggins theory. The cloud-points of dilute PAN solutions of the two systems were determined by titration method and those of concentrated PAN solutions from Boom’s linearized cloud-point correlation. Binary interaction parameters were calculated and optimized to construct the theoretical phase diagram. The obtained diagrams were used to investigate the effects of the non-solvent species on the formation of PAN fibers. If the non-solvent water is replaced with ethanol, the meta-stable two-phase region in the ternary phase diagram increases. This favors the de-mixing of the filament via nucleation and growth mechanism during the coagulation process, resulting in homogenous dense PAN fibers with low porosity.     

Studies on the mechanism of fine-structure development during industrial cellulose yarn production

A study has been made of the diffusion of zinc ions into alkaline solutions of sodium cellulose xanthate (viscose) when these are extruded into acidified salt solutions (spin-bath). Under these conditions, which exist during the manufacture of regenerated cellulose industrial yarns, the zinc ions are diffusing into a continuously coagulating gel structure from which water is exuded as the structure is developed. It has been shown that the presence of certain additives (modifiers) in the viscose can slow down the diffusion of both zinc and hydrogen ions, thus retarding the coagulation and neutralization of the viscose. In the initial stages of coagulation, before the neutralization point is reached, the modifiers reduce the rapid filament shrinkage and pressure rise within the filament which would otherwise be caused by the presence of zinc ions in the spinbath. The mode of action of the modifiers is discussed in the light of current theories. A hypothesis is put forward that the modifiers act by preventing the initial rapid shrinking action of the outer cuticle of the filament. This permits the production of the desired fine structure inside the filament during a slower steady shrinkage which leads to a round cross-sectioned filament of good mechanical properties.     

Diffusion of solvent from a cast cellulose acetate solution during the formation of skinned membranes

The transport of solvent out of a cast cellulose acetate (CA) solution into the coagulation bath during membrane formation is treated as a diffusion process. From the increase of solvent concentration in the bath with time (solvent leaching experiments) an overall solvent diffusion coefficient has been calculated. In size these coefficients compare well to mutual pseudo-binary solvent-non-solvent diffusion coefficients determined by means of a classical boundary broadening method applied to ternary solutions with fixed CA concentration, but with a gradient in solvent-nonsolvent composition. Since binary polymer-solvent interdiffusion coefficients are at least one order of magnitude lower, it is concluded that the diffusion of solvent into the coagulation bath is essentially a pseudo-binary solvent-non-solvent diffusion process. Combination of experimental results with model calculations for the effect of a thin dense skin on the diffusion of solvent out of the sublayer shows that the casting-leaching diffusion coefficient can be used to describe the out-diffusion of solvent from the layer under the skin provided that the relative skin resistance is not too high, or that the skin thickness is small.     

Strategy for self-assembly of the poly(9,9-dihexylfluorene) to microspheres: optimizing the self-assembling conditions

Self-assembly of π-conjugated polymers upon slow precipitation was comprehensively studied by suffusion of a vapor of non-solvents into polymer solutions. However, it was reported that only copolymers with steric hindrance in their backbone tended to form ordered spheres, while homopolymers having a single monomer component were hard to form ordered microstructure. This article presented here a strategy for the self-assembly of microspheres of a π-conjugated polymer having a single monomer component, e.g., poly(9,9-dihexylfluorene) (PDHF). The microspheres of PDHF were fabricated in the methanol vapor by the non-solvent vapor method. To obtain the optimized assembling parameters, the effect of self-assembling conditions including polymer concentration, the injection volume, the types of the non-solvent vapor, and solvent on the microstructural formation of PDHF were well investigated. The experimental results indicated that the increase of polymer concentration and injection volume led to the increase of partial aggregate of the spheres. Besides, the relatively uniform microsphere could be easily obtained with the concentration ranged from 2.5 to 5.0 mg/mL, and the injection volume of 5.0 μL in the methanol vapor. Furthermore, the polar solvent was advantageous to form well-ordered microspheres in the methanol vapor.     

Mathematical simulation of wet spinning coagulation process: Dynamic modeling and numerical results

A dynamic model of polymer wet spinning coagulation process is proposed in this article. The model is based on the double diffusion phenomenon, phase separation process, continuity balance, and momentum balance of the entire coagulation process. The uniqueness of the model lies in its dynamic feature. The model can simulate the system's dynamic response to variations in system inputs/parameters. Steady‐state system solutions can also be produced as the long‐time solutions of the dynamic model; a settling time can be observed at the same time. This paper employs a computationally efficient method of lines numerical algorithm for solving the dynamic model. A simulation experiment on a selected non‐solvent‐solvent‐polymer ternary system is carried out to verify the model as well as the numerical method. The dynamic simulation results are analyzed and discussed. At the end of the article, h‐refinement and p‐refinement are used to confirm the spatial convergence of the numerical solutions. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3432–3440, 2016     

湿纺凝固负拉伸对初生纤维结构与性能的影响

研究了凝固负拉伸对聚丙烯腈(PAN)纺丝液的膨胀效应、初生纤维聚集态结构和性能的影响,初步揭示了膨胀效应和凝固取向的产生机理及其对初生纤维结构与性能的影响;指出溶剂与水之间的传质速率差是控制初生纤维结构进而控制其性能的最关键因素,它决定了原液细流表面凝固层的组成及结构,而凝固速率反映了凝固层的生长速度。研究发现:随着凝固负拉伸的降低,PAN纺丝液的挤出胀大比减小,其传质速率差与凝固速率均下降,初生纤维的凝固取向、结晶度和晶粒尺寸均增加,其截面形状趋于圆形,内部结构变得均匀致密、缺陷减少,从而使断裂强度得以提高。     

Dissolution and wet spinning of silk fibroin using phosphoric acid/formic acid mixture solvent system

Regenerated silk fibroin (SF) filaments could be prepared by wet spinning in common solvent/coagulation system. SF was directly dissolved in mixture solvent of phosphoric acid and formic acid (20/80–30/70 ratio) and coagulated in methanol bath. The concentration and stability of SF dope solution have been studied by varying the mixture ratios of these solvents in accordance with elucidating the role of formic acid in the mixture solvent system. Morphological structure as well as crystalline structure of the regenerated filament was examined using SEM and XRD analyses. As a result of tensile test, the regenerated SF filament, which was made by one‐step dissolution and coagulation process, had good mechanical properties, 2.3 gf/d tenacity and 18% breaking strain. In this study, a simple wet spinning method which enables to apply to practical production has been reported for the preparation of the regenerated SF filament. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Nitrogen-doped porous carbon microspherules as supports for preparing monodisperse nickel nanoparticles

N-doped porous carbon microspherules were developed through controlled carbonization of the copolymer of vinylidene chloride and acrylonitrite. The carbon precursors were prepared by an inorganic-organic hybrid route. Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS) analysis showed the formation of N-doped carbon spherules. N₂ sorption analysis showed that the resultant carbon materials have a BET surface area of 692 m²/g. Nickel nanoparticles supported over them are kept in a well-dispersed state. Electron Probe Microanalysis (EPMA) and Transmission Electron Microscopy (TEM) showed nickel nanoparticles are quite monodisperse. Analysis of XPS spectra of the samples with different surface nitrogen atomic concentration demonstrated that nitrogen species on the carbon surfaces have a great impact on the dispersion state of the mounted metal nanocrystals.     

Performance control of asymmetric poly(phthalazinone ether sulfone ketone) ultrafiltration membrane using gelation

We studied the influence of the gelation conditions on the formation kinetics of the polyphthalazine ether sulfone ketone (PPESK) membrane via wet phase inversion process experimentally and theoretically. Membrane formation and its morphology were first observed with an online optical microscope - CCD camera system. The resulting membranes prepared under various gelation conditions were then characterized by the gelation parameter, optical microscope, and SEM. Lastly, the relationship between the final membrane structure/permeation properties and the gelation parameter was discussed extensively. The results showed that both the gelation rate and the membrane flux increased dramatically as the gelation temperature increased. Moreover, the membrane structures became loose, and the porosity of membrane increased. Different non-solvent could change the solubility parameter between the polymer and the non-solvent, and thus the gelation rate greatly. With the increasing number of carbons in non-solvent, the gelation rate became slow, and the membrane gradually changed from a finger structure into a sponge structure. Adding NMP into the non-solvent changed the difference in the chemical potential and the solubility parameter between the polymer solution and the non-solvent, which in turn changed the gelation rate of polymer solution greatly. With the increasing concentration of NMP in non-solvent, the gelation rate became very slow and sponge structures formed with the non-solvent system of 80% NMP. A novel conclusion could be made that we could control the flux and reject of membrane just by changing the mean diffusion coefficient of skin, D, and the diffusion coefficient of skin, D1, in the process of membrane formation. This work was presented at 13 ^th YABEC symposium held at Seoul, Korea, October 20–22, 2007.