喷头拉伸对三角形PAN纤维湿法凝固成形的影响

采用三角形喷丝孔,在二甲基亚砜(DMSO)水溶液凝固成形过程中,研究了不同喷头拉伸比对聚丙烯腈(PAN)初生纤维的截面形状和表面形貌、声速、结晶度以及力学性能的影响。结果表明:当喷头拉伸比增大到0.9倍时,初生纤维的截面的"角部钝化"现象消失,截面变形为和喷丝孔相似的形状;与此同时,初生纤维的力学性能也发生了显著的变化;而且,随着喷头拉伸比的增加,初生纤维的声速取向、结晶度及晶粒尺寸都逐渐增加。     

Effect of DMSO/H2O coagulation bath on the structure and property of polyacrylonitrile fibers during wet‐spinning

The effect of coagulation bath condition on the structure and property of the nascent fibers and polyacrylonitrile fibers during wet‐spinning is studied. The best coagulation condition to produce polyacrylonitrile fibers has been found by examination of EA, XRD, SEM, and so on. The results indicated that when the coagulation bath was DMSO/H₂O system, the temperature was 60°C, the concentration was 65%, the minus stretch ratio was ?10%, fine crystallites and high degree of crystallization in the nascent fibers and polyacrylonitrile fibers could be achieved, and less solvents remained in the nascent fibers with circular cross section morphology. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Study on the Coagulation Process of Polyacrylonitrile Nascent Fibers during Wet-spinning

Summary The coagulation process of polyacrylonitrile (PAN) precursor during wet-spinning was studied by chemical method based on the KMnO₄ titration. Experiments were performed with gelled solutions of PAN in dimethyl sulphoxide (DMSO) to determine the diffusion rate of solvent during the coagulation. The experimental datas about solvent diffusion coeffecient were calculated by using diffusion equation, which reflected the coagulation process of nascent fibers. At the same time, the effects of coagulation on the residual solvent content, the change of morphology of nascent fibers, the crystallization degree and the stress-strain curves were studied by use of X-ray diffraction, SEM, single fiber tensible test and so on. The results elucidated the relationship between coagulation process and the structure and property of PAN nascent fibers.     

干喷湿纺中聚丙烯腈初生纤维断裂行为研究

为了系统研究干喷湿纺中聚丙烯腈初生纤维的拉伸行为,利用SEM、纤维强伸度仪、XRD等手段,分析了凝固浴拉伸比、拉伸速率、微观结构和缺陷等对初生纤维断裂行为的影响。结果表明,干喷湿纺中,凝固浴拉伸比的提高有利于增加初生纤维的结晶度和断裂延伸率;同时发现,初生纤维内外部的缺陷以及拉伸的速率对初生纤维的断裂行为有重要影响。     

Morphological studies on extruded films and filaments of polypropylene

In the present work, an attempt has been made to study the development of morphology during extrusion and uniaxial stretching of polypropylene (PP) films and filaments at corresponding conditions. Dies for extrusion of films and filaments were designed to achieve similar extrusion velocity and shear rates. Orientation in films and fibers of PP produced from these dies was determined by birefringence and wide-angle X-ray diffraction (WAXD). The degree of crystallinity was determined by density and WAXD. The superstructure developed during extrusion was studied in films by small-angle light scattering. It was inferred that films and fibers prepared under similar conditions would produce similar morphology. Hence, films can be characterized by optical techniques when it is difficult to study fibers. © 1994 John Wiley & Sons, Inc.     

三元共聚聚酰亚胺初生纤维结构与性能的研究

以BTDA-TDI/MDI(P84)三元共聚聚酰亚胺(PI)粉末为原料,采用湿法纺丝技术制备BTDA-TDI/MDI三元共聚PI初生纤维,并对其结构和性能进行表征。实验结果表明:三元共聚PI初生纤维的最高抗断裂强度为0.65 cN/dtex;纺丝浆液PI质量分数19%时所得初生纤维表面较光滑;凝固浴溶液NMP质量分数70%时初生纤维结晶度分别比质量分数60%和80%时结晶度大;不同NMP质量分数凝固浴溶液所得初生纤维的热稳定性相差不大。     

Effect of the solvent type on the formation and physical properties of polyacrylonitrile fibers via a solvent‐free coagulation bath

Polyacrylonitrile (PAN) fibers were fabricated via a dry‐jet wet‐spinning technique, and a solvent‐free coagulation bath system was adopted. The effects of different types of dope solvent on the formation and physical properties of the PAN fibers were investigated. Dimethylformamide and dimethyl sulfoxide (DMSO) were selected as the solvents and were added to a spinning solution consisting of 18 wt % PAN. The PAN fibers were examined with field emission scanning electron microscopy, differential scanning calorimetry, and thermogravimetric analysis. The field emission scanning electron micrographs revealed that the PAN fibers with the DMSO solvent exhibited a more circular shape and a smoother skin. The PAN fibers with the DMSO solvent had their glass‐transition temperature (T_g) at 121°C. This study indicated that the different types of dope solvent used in the dope preparation did not affect T_g of the PAN fibers because of the solvent‐free coagulation bath system; however, they significantly affected the physical formation of the PAN fibers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of coagulation on the structure and property of PAN nascent fibers during dry jet wet-spinning

The paper has studied the effect of coagulation process on the structure and property of polyacrylonitrile nascent fibers during dry jet wet-spinning. The coagulation process to form polyacrylonitrile fibers has been studied by examination of FTIR, XRD, and SEM and so on. The results indicated that compared with coagulation directly, polyacrylonitrile nascent fibers gradually formed with fine crystallites and high degree of crystallization were achieved, the flex vibration peak of S=O gradually decreased, and less solvents remained in the nascent fibers with compact cross section morphology. At the same time, nascent fibers with less DMSO under different draw ratios showed higher fracture intensity and lower elongation.     

超大长径比双螺杆挤出机制备聚丙烯腈初生纤维

采用自主研发的超大长径比(136)双螺杆挤出机实现了PAN初生纤维的纺丝制备,研究了PAN粉料质量分数(16％、20％、24％)、双螺杆挤出机机筒温度(50、60、70 ℃)、循环挤出次数(0、1、2)对PAN初生纤维力学性能及表面形貌的影响.结果表明,PAN初生纤维的拉伸强度随质量分数、机筒温度和循环挤出次数的增加而...     

Two‐dimensional simulation of hollow fiber membrane fabricated by phase inversion method

In the steady fabricating process, two‐dimensional hollow fiber membrane near the spinneret was numerically simulated using the finite element method (FEM). The unknown positions of free surface and moving interface were calculated simultaneously by the velocity and pressure fields. The effects of seven relevant parameters, i.e., inertia term, gravity term, dope flow rate, bore flow rate, dope viscosity, tensile force, end velocity and non‐Newtonian on the velocity and diameter profile were studied. On the basis of the simulated results, the inertia term in hollow fiber‐spinning process was safely neglected in low speed, while the effect of gravity was not be neglected. Besides, the outer diameter of the fibers increased with an increase of dope flow rate and bore flow rate; Large tensile force or large end velocity could cause large deformation in the air gap; larger viscous dope solution tended to make less deformation in the air gap. It was found that an increase of the dope flow rate at small dope flow rate resulted in an increase of the inner diameter, while at large dope flow rate, it decreased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2067–2074, 2006     

喷丝速度对PAN中空纤维成形的影响

研究了于湿法纺丝工艺中喷丝速度对聚丙烯腈(PAN)中空初生纤维成形与性能的影响.结果表明:喷丝速度对PAN纤维截面的规整性、表面形貌、异形度、声速取向和致密性等均会产生影响.在喷丝速度为0.20～0.45m/min时,PAN纤维中空度与声速取向随着喷丝速度的增加而快速增加,随后其增幅逐渐变小或基本不变.纤维内表面在较高的喷丝速度下会产生条纹、粗糙度增大,纤维外表面无明显变化.     

Uniformity control and ultra-micropore development of tubular carbon membrane for light gas separation

Tubular carbon molecular sieve (CMS) membranes have been recognized as a potential module for commercial application due to its high mechanical strength and large surface area. However, the carbon layer uniformity was restricted by substrate texture and dope fluidity when the dip-coating method was used. This study evaluated the influence of various parameters of dip-coating with an integrated vacuum-assisted system, including solvent vaporization rates, vertical immersion/withdrawal velocity, vacuum degree, dope composition, coating cycles on the microstructure, and gas separation performance of CMS membranes. Using vacuum assistance and a low-vaporization solvent minimized the influence of viscosity and gravity on dope fluidity as a result of fast phase inversion. The as-prepared tubular CMS membranes showed enhanced perm-selectivity according to a H₂/N₂ gas selectivity of 8.8, a CO₂/N₂ gas selectivity of 6.7, a H₂ permeability of 464 barrer, and a CO₂ permeability of 356 barrer.     

Improved microstructure of asymmetric niobium pentoxide hollow fiber membranes

Asymmetric niobium pentoxide (Nb₂O₅) hollow fiber membranes were prepared by the phase inversion and sintering process at temperatures ranging from 1000 to 1350°C. The effects of extrusion parameters on the morphology and properties of the produced membranes were systematically explored. Asymmetric hollow fibers with regular inner contour were obtained at extrusion flow rates of 15 and 25 ml min⁻¹ of ceramic suspension and internal coagulant, respectively. Hollow fibers sintered at temperatures greater than 1200°C presented modifications in the morphology of Nb₂O₅ grains, which were also evidenced by X-ray diffraction and Raman analyses. Hollow fibers produced with an air gap of 50 mm presented a dense outer sponge-like layer and micro-voids formed from the inner surface. These hollow fibers sintered at 1200°C presented suitable bending resistance and water permeability (24.2 ± 0.60 MPa and 3.00 ± 0.01 L h^-1 m^-2 kPa^-1, respectively). The outer sponge like layer was mitigated when the fibers were produced without air-gap.     

Diverse morphologies of PVDF hollow fiber membranes and their performance analysis as gas/liquid contactors

A systematic investigation on the morphology development of polyvinylidene fluoride hollow fiber membrane made using various N‐methyl‐2‐pyrrolidone (NMP) aqueous solutions as an inner coagulant was carried out. The cross‐sectional and inner surface morphology were analyzed with scanning electronic microscopy (SEM). It is found that with increase on NMP concentration, the morphology of the resultant membranes gradually shifted from a double‐skin to a single‐skin structure. When 40.0 ～ 55.0 wt.% NMP solution was used, some unexpected macrovoids near the inner region were observed. This special morphology feature was attributed to the reduced solidification rate of the inner surface as a result of increase on NMP concentration, which sharply weakened the inner skin strength. While the existence of centralized stress formed in the phase inversion process, such as shrinkage stress from syneresis, resulted in fractured points in the nascent skin surface that finally made it difficult to maintain a uniform structure. Investigations on effects of the dope flow rate and the bore fluid velocity on the morphology of PVDF fiber membranes experimentally confirmed the suggestion. Three model membranes with double skins, single skin and single skin with macrovoids structures, respectively, were used to test their permeation performance in a CO₂ membrane contactor system. The experimental results show the membranes without an inner skin present higher permeability and lower mass transfer resistance than the membrane with a double skin structure. © 2010 Wiley Periodicals, Inc. Journal of Applied Polymer Science, 2010     

Computer modeling of isothermal crystallization in short fiber reinforced composites

Computer modeling and simulation for the isothermal crystallization of short fiber reinforced composites with athermal nucleation is presented. The “pixel coloring” technique which is capable of capturing the morphology evolution and calculating the crystallization kinetics is implemented. A parametric study is used to explore the influences of fibers on the crystallization in the reinforced system. The results indicate that the fibers depress the crystallization rate when compared to that of neat polymers or accelerate the crystallization rate by providing nucleation sites. The constraining effect is mainly dependent on fiber content while the enhancing effect is mainly determined by fiber surface and fiber nucleation density. Fiber orientation has almost no effect on the crystallization kinetics but changes the ultimate morphology. Fiber length and fiber diameter have different influences on crystallization kinetics and mean size of spherulites. Results show that fiber diameter affects the crystallization much more than that of fiber length.     

Crystallinity development in polyacrylonitrile nascent fibers during coagulation

This paper has studied the crystal and thermal property of nascent fibers during the polyacrylonitrile coagulation process. A water (H₂O)/dimethyl sulphoxide (DMSO) mixture was used as the coagulation bath for the coagulation process of acrylonitrile(AN)/itaconic acid(IA) copolymer fibers in the study. By transforming the spinning conditions, especially air gap distance between the spinneret and coagulation bath, draw ratios, coagulation time, we received the crystal and thermal properties of nascent fibers under different conditions. The relationship between the property of nascent fibers and the spinning conditions has been studied by use of X-rays, SEM, differential scanning calorimetry (DSC) and so on. The results indicated that the degree of crystallization gradually increased with the rise of coagulation time and tended to a fixed value when reached some time. With the augment of draw ratios, the crystal degree appeared differently, in which it decreased when the air gap distance was 0 mm and it increased when the air gap distance was 1 mm and 2 mm. At the same time, the thermal properties showed little difference in peak position and biggish difference in heat energy, which indicated the ability to endure heat for latter spinning process and thermal stabilization process.     

SEBS-g-MAH和EP复合增容PA610/PC合金的研究

选用SEBS-g-MAH和EP为复合增容剂,采用熔融挤出的方法制备了PA610/PC合金,研究了该合金的力学性能、熔融结晶及微观结构形态。结果表明,当PA610/SEBS-g-MAH(EP)/PC组分比为75/9(2)/25时,合金的冲击强度比不加增容剂时提高了281.4%,断裂伸长率提高了346.0%。而增容剂的加入使合金中PA610的结晶温度升高,结晶速率增大而结晶度降低,由于异相成核作用使结晶发生细化,使得韧性提高、熔点降低。微观结构形态研究表明,在只加入SEBS-g-MAH的PA610/PC合金中,合金断面有很多PC被拔出及余留空洞的现象;在加入EP协同增容后,PC被拔出的现象减少,与PA610基体的界面粘合增强,空洞消失。     

湿纺工艺纺制PAN中空纤维成形机理研究

利用C型喷丝板进行挤出凝固,采用湿法纺丝工艺制备聚丙烯腈(PAN)中空纤维,从PAN/二甲基亚砜(DMSO)纺丝原液的流变性能和凝固过程的相分离两个方面探讨了PAN中空纤维的成形机理。结果表明:纺丝液随剪切速率(γ)的增加逐渐发生由粘性向弹性的转变是挤出胀大的主要原因,其粘弹转变点随着温度的升高而向高γ移动,在60℃下的纺丝液弧片接触成孔的理论临界γ为212 s~(-1);纺丝液在凝固浴中表层成膜是PAN-DMSO-H_2O三元体系相分离的结果,纺丝液细流表面成膜速度是影响孔结构闭合的重要因素,可以通过凝固浴浓度和凝固浴调节剂来控制。     

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。     

Investigation on the effect of spinning conditions on the properties of hollow fiber membrane for hemodialysis application

Polyethersulfone (PES) hollow fiber membranes were fabricated via the dry‐wet phase inversion spinning technique, aiming to produce an asymmetric, micro porous ultrafiltration hollow‐fiber specifically for hemodialysis membrane. The objective of this study is to investigate the effect of spinning conditions on the morphological and permeation properties of the fabricated membrane. Among the parameters that were studied in this work are air gap distance, dope extrusion rate, bore fluid flow rate, and the take‐up speed. The contact angle was measured to determine the hydrophilicity of the fibers. Membrane with sufficient hydrophilicity properties is desired for hemodialysis application to avoid fouling and increase its biocompatibility. The influences of the hollow fiber's morphology (i.e., diameter and wall thickness) on the performance of the membranes were evaluated by pure water flux and BSA rejection. The experimental results showed that the dope extrusion rate to bore fluid flow rate ratio should be maintained at 1:1 ratio to produce a perfectly rounded asymmetric hollow fiber membrane. Moreover, the flux of the hollow fiber spun at higher air gap distance had better flux than the one spun at lower air gap distance. Furthermore, spinning asymmetric hollow fiber membranes at high air gap distance helps to produce a thin and porous skin layer, leading to a better flux but a relatively low percentage of rejection for BSA separation. Findings from this study would serve as primary data which will be a useful guide for fabricating a high performance hemodialysis hollow fiber membrane. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43633.