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.     

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.     

Study on the Coagulation Mechanism of Wet-Spinning PAN Fibers

The mechanism of coagulation process of polyarylonitrile (PAN) wet-spinning was studied based on the numerical analysis of the coagulation of viscous polymer solution by diffusional interchange with a bath. Experiments were performed in order to determine the diffusion coefficient of solvent and non-solvent. The numerical solutions of Fick’s second law equations for diffusion were obtained by using the MOL method. The microstructure of nascent fibers is investigated by Transmission Electron Microscope (TEM) and Electron Probe Microanalyser (EPMA). It is found that the speed of outflow solvent is more rapid than that of influent non-solvent. The speed of concentration change of solvent and non-solvent is rapid in outside layers of filament (0.2R) and slow in inner layers. The solvent concentration is keeping a high value at the center of filament. TEM and EPMA show that the microstructure is a typical layered structure. The thickness of dense skin is about 0.2R. The core region of fiber is very loose.     

Kinetics of diffusion in polyacrylonitrile fiber formation

A H₂O/dimethyl sulfoxide (DMSO) mixture was used as the coagulation bath of the wet‐spun process for polyacrylonitrile fibers. Diffusion behaviors of coagulate and solvent of the protofibers were studied. Diffusion coefficients of H₂O and DMSO of the protofibers, prepared by acrylonitrile (AN) homopolymers, were also determined. It was found that diffusion coefficients of H₂O and DMSO in the protofibers prepared by AN homopolymers, synthesized by DMSO solution polymerization, are highest compared with those of AN homopolymers synthesized by H₂O/DMSO mixture suspension polymerization and aqueous suspension polymerization. With increasing polyacrylonitrile concentration in the dope, diffusion coefficients of H₂O and DMSO decreased continuously. Diffusion coefficients of H₂O and DMSO increased concomitantly with increasing bath temperature, but the changes of diffusion coefficient values were less prominent when the temperature increased beyond 60°C. When DMSO concentration in the coagulation bath was 55 wt %, the values of diffusion coefficients of H₂O and DMSO were minimal. Diffusion coefficients increased with increasing jet stretch minus ratio. When the protofiber radius was increased, there was a corresponding increase of diffusion coefficients of H₂O and DMSO. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1529–1533, 2005     

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     

间位芳纶溶解及凝固性能研究

以二甲基乙酰胺(DMAc)、二甲基甲酰胺(DMF)、二甲基亚砜(DMSO)、1-甲基-2-吡咯烷酮(NMP)为溶剂,分别加入LiCl和CaCl_2制备溶解体系,研究了间位芳纶在这几种溶解体系中的溶解性能。再以H_2O-DMAc、H_2O-DMF、H_2O-DMSO、H_2O-NMP为凝固浴,研究了溶剂种类、芳纶溶液质量分数、离子浓度等对间位芳纶溶液的凝固性能的影响。结果显示:Li Cl-DMAc溶解体系具有更强的溶解性能;凝固值随凝固浴中凝固剂H_2O的含量的增加不断减小,而临界浓度几乎没有变化;随着凝固浴温度的增加,凝固值增大,临界浓度减小;凝固值随凝固浴中离子浓度的升高而增大,但临界质量分数则不断降低。另外,间位芳纶溶液的扩散系数随着凝固浴中H_2O的含量的减少不断减小,随着芳纶浓度的增加不断减小。     

Diffusion coefficient of DMF in acrylic fiber formation

A H₂O/dimethyl formamide (DMF) mixture was used as the coagulation bath of wet‐spun process for acrylic fibers. Diffusion coefficient of DMF in the protofibers prepared by acrylonitrile/acrylamide copolymers was determined. It has been found that diffusion coefficient of DMF outflow of the protofibers prepared by acrylonitrile/acrylamide copolymers synthesized by solution polymerization is highest compared with those of acrylonitrile/acrylamide copolymers synthesized by H₂O/DMF mixture suspension polymerization and aqueous suspension polymerization. With an increase of copolymer concentration in the dope, diffusion coefficient of DMF decreases continuously. Diffusion coefficient of DMF increases along with the bath temperature, but the changes in diffusion coefficient values are less prominent as temperature goes beyond 55°C. When DMF concentration in the coagulation bath was 50%, the value of the diffusion coefficient of DMF was minimal. Diffusion coefficient of DMF increases along with jet stretch minus ratio increase. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3616–3619, 2006     

Diffusion coefficient of DMSO in polyacrylonitrile fiber formation

A H₂O/dimethyl sulfoxide(DMSO) mixture was used as the coagulation bath for the wet‐spun process of acrylonitrile/ammonium itaconate copolymers fibers. Diffusion coefficient of DMSO in the protofibers prepared by acrylonitrile/ammonium itaconate copolymers was determined. It has been found that diffusion coefficient of DMSO outflow of the protofibers prepared by acrylonitrile/ammonium itaconate copolymers synthesized by the solution polymerization is highest compared with those of acrylonitrile/ammonium itaconate copolymers synthesized by H₂O/DMSO mixture suspension polymerization and the aqueous suspension polymerization. With an increase of copolymer concentration in the dope, diffusion coefficient of DMSO decreases continuously. Diffusion coefficient of DMSO increases along with the bath temperature, but the changes of diffusion coefficient values are less prominent as temperature goes beyond 60°C. When DMSO concentration in the coagulation bath was 55 wt %, the value of the diffusion coefficient of DMSO was minimal. Diffusion coefficient of H₂O increases with the jet stretch minus ratio increasing. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4447–4451, 2006     

纤维素/磷酸/多聚磷酸液晶溶液的凝固性能

通过捏合机制备了纤维素在磷酸/多聚磷酸复合溶剂中的液晶溶液。讨论了纤维素在该溶剂体系中的溶解性能。利用显微镜观察法测定了该液晶溶液在丙酮、乙醇、正丙醇、乙酸乙酯、乙二醇的凝固浴中凝固层厚度随时间的变化。结果表明:在所有的凝固浴中凝固层厚度与时间的平方根成线性关系,且相关系数很高。利用菲克定律为基础的一维扩散模型对实验数据进行分析,表明所采用的凝固厚度的测试方法准确,凝固速度可作为表征凝固过程的合理参数。     

聚丙烯腈基碳纤维原丝在干湿法纺丝中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。通过Fick定律建立了纺丝液溶剂扩散的数学模型,得出了溶剂沿纤维原丝的径向分布,还讨论了各种因素对溶剂质量分数分布的影响。     

Pore generation in asymmetric polymeric membranes Correlation with solvent mobilities

Summary Analyzing videomicroscopy observations, this work deals with macrovoids detected through the skin of asymmetric polymeric membranes. The circle-like images of the macrovoids were found to form two-dimensional random patterns ; these were characterized from the mean distance, <λ>, determined between nearest neighboring images. Starting from polyetherimide or polyacrylonitrile solutions, each solution cast as a film was immersed in a water bath, at room temperature ; <λ> was shortened either by increasing the solvent concentration in the casting solution or by decreasing the solvent concentration in the bath (non-solvent of the polymer). This study was based on the assumption that the formation of the macrovoid pattern may be correlated to the interface instability resulting from the current of solvent diffusing towards the bath and initiated by the immersion of the polymer solution. Master curves, involving <λ>, the solvent concentrations in the polymeric solutions or in the bath and the solvent diffusion coefficients, measured prior to the immersion of the solution in the bath, were drawn. Diffusion coefficients were measured using a pulsed magnetic field gradient method. Received: 6 November 1998/Revised version: 9 February 1999/Accepted: 9 February 1999     

Determination of the Diffusion Coefficient of H<Subscript>2</Subscript>O in Polyacrylonitrile Fiber Formation

An H₂O/dimethyl sulphoxide (DMSO) mixture was used as the coagulation bath of a wet-spun process. The diffusion coefficient of H₂O in the protofibers prepared by acrylonitrile homopolymers was determined. It was found that the diffusion coefficient of H₂O in the protofibers prepared by homopolymers synthesized by solution polymerization was highest compared with those of homopolymers synthesized by H₂O/DMSO mixture suspension polymerization and aqueous suspension polymerization. With an increase of polyacrylonitrile concentration in the dope, the diffusion coefficient of H₂O decreased continuously. The diffusion coefficient of H₂O increased along with the bath temperature, but the changes of diffusion coefficient values were less prominent as the temperature went beyond 60^○C. When the DMSO concentration in the coagulation bath was 55%, the value of the diffusion coefficient of H₂O was minimal. The diffusion coefficient of H₂O increased with increasing jet stretch minus ratio. When the protofiber radius was increased, there was a corresponding increase of the diffusion coefficient of H₂O.     

Influences of diffusion coefficient of 1-allyl-3-methylimidazolium chloride on structure and properties of regenerated cellulose fiber obtained via dry-jet-wet spinning

The diffusion dynamics of the cellulose/1-allyl-3-methylimidazolium chloride ([Amim]Cl) solution during coagulation of regenerated cellulose fiber in a nonsolvent bath was investigated in detail. According to Fick's second law of diffusion, the experimental data were fitted to obtain the diffusion coefficients of [Amim]Cl (D). The cellulose concentration, bath type, and temperature were varied to analyze their influence on the diffusion coefficient of [Amim]Cl. Furthermore, the dependence of the structure and properties of the regenerated fiber obtained via dry-jet-wet spinning on the diffusion coefficients were analyzed. Many defects were formed in the surface and cross sections of the regenerated fibers prepared with high diffusion coefficients. The crystallization and mechanical properties deteriorated with the increase in the diffusion rate of [Amim]Cl. Therefore, the diffusion coefficients of [Amim]Cl should be kept relatively low to enable the preparation of uniform-structured regenerated cellulose fibers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47609.     

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。     

Sorption kinetics of p-nitrophenol by oxidized undrawn nylon filaments

The sorption kinetics of p-nitrophenol (PNP) onto undrawn nylon yarn from an organic, nonswelling solvent in a dye bath in which the concentration of PNP was being depleted were found to obey Hill's solution of the diffusion equation, suggesting the presence of a monolayer of absorbed PNP at the surface of the fiber. Diffusion coefficients were obtained using a nonlinear least-squares curve-fitting computer program. For undrawn nylon samples, oxidized for various lengths of time prior to dyeing, the diffusion coefficient increased as a function of oxidation time, rising particularly rapidly once the fibers developed microscopically visible surface cracks. The dependence of diffusion coefficient on oxidation time implies that oxidative degradation of the material is accompanied by formation of submicroscopic incipient cracks, permeable by PNP, of which at least some eventually develop into visible cracks after sufficient oxidation.     

Preparation and gas separation properties of asymmetric polysulfone membranes by a dual bath method

Defect-free skinned asymmetric gas separation membranes were prepared by a dual bath coagulation method that is a wet/wet phase inversion technique. The membranes were cast from a polysulfone/N,N-dimethylacetamide solution. In two sequent nonsolvent baths, the first bath using iso-propanol (IPA) leads to the formation of a dense skin top layer and the second bath using water makes the actual polymer precipitation. The top skin layer thickness was governed by changing the immersion time of the first IPA bath. We suggest that the growth rate of the skin layer is to be determined by a diffusion process.     

凝固浴氨化对PAN湿法纺丝凝固行为的影响

在二甲基亚砜/水(DMSO/H_2O)凝固体系中加入氨水,以pH值控制凝固浴氨化程度,研究了凝固浴氨化对聚丙烯腈(PAN)湿法纺丝凝固行为的影响;采用扫描电子显微镜表征PAN初生纤维的皮层结构,采用卡尔费休水分仪和气相色谱仪研究了氨化对水和DMSO扩散系数的影响。结果表明:当凝固浴pH值为8.0时,PAN初生纤维的皮层最薄;随着凝固浴pH值的增大,水的扩散系数逐渐减小,DMSO的扩散系数(D_(DMSO))先减小后增大,当pH值为8.0时,D_(DMSO)出现最小值;氨化的作用机理是通过氨与水和DMSO分子间的氢键作用来实现的。     

Effect of coagulation conditions on solvent diffusions and the structures and tensile properties of solution spun polyacrylonitrile fibers

Polyacrylonitrile (PAN) fibers were spun by solution spinning. In this work, two coagulation compositions, dimethyl sulfoxide (DMSO)/water and methanol, were used, and coagulation temperatures were varied from ?20 to 0 to 20 °C. The coagulation compositions and temperatures strongly affected the solvent diffusion processes, the structures of as‐spun fibers, and the tensile properties of final drawn fibers. When DMSO/water was used as coagulation bath, non‐solvent (water) diffused into PAN fibers and led to a quick PAN solidification. By comparison, when methanol was used as coagulation bath, no or minimal amount of methanol diffused inward to the fibers. The different solvent diffusion behaviors in DMSO/water and methanol baths led to different structures of as‐spun PAN fibers. It was observed that the tensile properties of final drawn fibers strongly depended on the coagulation conditions. When methanol was used as coagulation bath and the bath temperature was ?20 °C, PAN fibers was found to possess the best tensile properties, a tensile strength of 0.89 GPa and young modulus of 20.4 GPa. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44390.     

纤维素/NMMO溶液及其薄膜的制备与性能研究

以水质量分数为13.3%的N-甲基吗啉-N-氧化物(NMMO)为溶剂溶解棉浆粕,制备质量分数为5%～11%的纤维素/NMMO溶液。将所得溶液制备纤维素薄膜,考察了纤维素/NMMO溶液的稳定性,研究了凝固浴温度和组成对纤维素薄膜的成膜性、断面形态及力学性能的影响。结果表明:纤维素/NMMO溶液随着浓度增大,其粘度先增大后减小,再急剧上升;纤维素/NMMO溶液在玻璃介质中稳定性较好,微量Cu~(2+),Fe~(3+)等杂质存在时,其稳定性显著下降;纤维素薄膜随凝固浴温度升高,其透明性、拉伸强度和断裂伸长率均下降;相对于水,含有乙醇和NMMO的凝固浴能减缓双扩散的速度,使纤维素薄膜的拉伸强度略有提高,断裂伸长率出现不同程度下降。     

Preparation of defect-free asymmetric membranes for gas separations

A technique was developed to prepare defect-free, asymmetric, polymer membranes for gas separation. The preparation method eliminates the need for coatings, which are usually required to render asymmetric, polymer based, membranes gas selective. In this method, a casting solution containing a polymer, solvent, and salt additive is given a desired shape and immersed in a coagulation bath containing a nonsolvent. The nonsolvent is selected to have a low affinity for both the solvent and salt additive. After the complete coagulation of the membrane, the additive salt is leached out in a second bath. This leads to the formation of an asymmetric membrane that has a well-interconnected porous network. The fine membrane structure is preserved by solvent exchange before it is finally dried. Polyetherimide (PEI) (Ultem® 1000) membranes were prepared from casting solutions containing 23, 25, and 26.5% (wt) PEI, various amounts of lithium nitrate and N-methyl-2-pyrrolidinone (NMP). Membrane performance was determined for the separation of oxygen from air. The effects of polymer concentration, additive salt concentration and the drying process on oxygen permeance, and the actual separation factor of the membrane are discussed. The addition of a small amount of solvent to the coagulation bath improved the leaching of the salt additive and produced membranes with a more open structure. A polymer concentration of 23% produced membranes with the highest performance. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1471–1482, 1999