湿法纺丝凝固负牵伸的研究

采用膨口胀大比的测量、沸水收缩率、X射线衍射、电子探针、孔隙率及机械性能的测试等分析测试手段,系统研究了凝固负牵伸对聚丙烯腈(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。研究发现:随着凝固负牵伸的降低,PAN纺丝液的膨口胀大比减小,初生纤维的凝固取向、结晶度和晶粒尺寸均增加,其截面形状趋于规整,内部结构变得均匀致密、内部缺陷减少。     

凝固条件对PAN初生纤维微结构的影响

通过湿法纺丝工艺制备聚丙烯腈(PAN)初生纤维,借助于X射线衍射仪、声速仪、扫描电子显微镜、小角X光散射仪等,研究了凝固浴温度、凝固浴浓度、喷丝头拉伸等凝固条件对初生纤维晶态结构、取向结构、形态结构的影响。结果表明:PAN纤维的凝聚态结构和形态结构在初生纤维形成时已基本形成;PAN初生纤维的结晶度达40%以上,其结晶度和结晶尺寸受凝固浴温度和浓度的影响;PAN初生纤维和原丝的晶区取向和全取向随着喷丝头拉伸的增大而增大;PAN初生纤维具有沿纤维轴向高度取向的沟槽,通过改变成形条件,可以获得沟槽浅且规整性完美的纤维表面;提高凝固浴浓度,可以形成结构均质、致密的PAN初生纤维,避免皮芯结构及芯部出现较多孔洞。     

沸水再拉伸速率对聚丙烯腈纤维结构与性能的影响

以1-丁基-3-甲基咪唑氯盐([BMIM]Cl)为溶剂溶解聚丙烯腈(PAN)制成PAN纺丝原液,采用干喷湿法纺丝,经过凝固、预拉伸、沸水拉伸制得PAN纤维,对所得PAN纤维进行沸水再拉伸处理,研究了沸水再拉伸速率对PAN纤维结构和性能的影响。结果表明:PAN纤维中残留质量分数为4.38%的离子液体,为沸水再拉伸起到了增塑作用;随着沸水再拉伸速率的增大,PAN纤维的力学性能提高,断裂强度由2.69cN/dtex提高到4.33 cN/dtex,而断裂伸长率由26%减小到20%,纤维的玻璃化转变温度、晶区取向度、双折射率、结晶度、晶粒尺寸均增大。     

三角形PAN纤维湿法纺丝工艺研究

采用三角形喷丝板,以二甲基亚砜为溶剂,进行聚丙烯腈(PAN)湿法纺丝。探讨凝固成形条件及后拉伸对三角形PAN纤维截面形状、声速和力学性能的影响。结果表明:随着凝固浴浓度的升高,PAN初生纤维的异形度降低,声速和力学性能均先升高后降低;随着凝固浴温度的升高,PAN初生纤维的异形度增大,声速和力学性能均降低;随着喷丝头拉伸比的增加,PAN初生纤维的异形度增加,声速和力学性能也都呈上升趋势,随着后拉伸的进行,三角形PAN纤维的异形度基本保持不变,其力学性能和声速均逐渐升高。     

湿纺凝固条件对PAN初生纤维形态结构的影响

分析了凝固浴温度、浓度、表观负拉伸等凝固条件对聚丙烯睛初生纤维形态结构的影响规律及作用机理,得出最佳的凝固工艺参数。结果表明:在其他凝固参数不变时,凝固浴温度、浓度及表观负拉伸均存在各自的临界值,低于或超过此临界值,初生纤维及原丝的性能均下降;采用凝固浴温度60℃、凝固浴质量分数为65％的最佳凝固工艺参数,可获得截面圆形且结构致密的初生纤维,并制得力学性能优异的原丝。     

凝固与拉伸条件对PAN纤维结构形态的影响

应用X射线衍射仪、声速仪、密度梯度管及扫描电子显微镜研究了在不同凝固条件下拉伸对聚丙烯腈(PAN)纤维结构及表面形态的影响规律。结果表明,拉伸对纤维结构形态的影响受凝固条件不同而不同。在凝固速度较慢时,随着拉伸倍数的增加,纤维的结晶度和晶粒尺寸减小,纤维的取向增加先快后慢;在凝固速度较快时,随着拉伸倍数的增加,纤维结晶度先增加后减小,晶粒尺寸一直减小,取向增加呈S型。拉伸倍数的增大使得纤维的直径变细、表面粗糙度增加、密度增加。     

纺丝方式对PAN基碳纤维原丝形貌、结构及性能的影响

采用三种方式制备了PAN原丝,并利用扫描电镜、X射线衍射、 单丝拉力机等设备对纤维的形貌和结构进行了研究.实验结果表明,湿法纺丝工艺喷丝后即凝固,表面沟槽现象明显;干湿法和"准干湿法"工艺在非凝固相中完成巴拉斯挤出胀大效应才进入凝固浴,纤维表面光滑.湿法初生纤维的结晶度和取向程度高于其他工艺,随着后续牵伸和干燥致密化过...     

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。     

聚丙烯腈碳纤维原丝聚合及凝固成形的研究进展

综述了聚丙烯腈原丝聚合和湿法纺丝时凝固成形的国内外研究进展,简要介绍了聚合的方式、共聚和共混改性的研究进展,介绍了凝固成形中双扩散理论模型的建立与发展,重点讨论了凝固浴的组成及浓度、温度、拉伸比等因素对扩散及初生纤维结构与性能的影响。     

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。     

Effect of jet stretch on polyacrylonitrile as‐spun fiber formation

In this article, the effect of jet stretch ratio on the extrudate die‐swell effect of polyacrylonitrile spinning solution and the structure and properties of as‐spun fibers was systematically analyzed by means of X‐ray diffraction (XRD), electron microprobe analysis, and the measurement of die‐swell ratio, boiling‐water shrinkage, porosity, mechanical properties analysis, etc. It revealed the formation mechanism of the die‐swell effect and spin orientation and its influences on the structure and properties of as‐spun fibers. It showed that with the increase of the jet stretch ratio the die‐swell ratio became smaller, both the degree of spin orientation and the crystallinity increased, the microstructure of as‐spun fibers became compact and homogeneous, and the cross section tended to be circular. As a result, the breaking tenacity of as‐spun fibers and resultant precursors all increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3348–3352, 2007     

A study of shaped fiber formation

An experimental study has been carried out to investigate the effects of spinning conditions on the shape of fibers spun through noncircular spinnerette holes, namely, rectangular holes, trilobal holes, and round holes with lugs. For the study, bench-scale apparatuses of wet spinning and melt spinning were used which had been constructed in connection with an earlier study by Han. In the wet-spinning experiment, the spin dope used was an aqueous solution of polyacrylonitrile (PAN) consisting of approximately 10% polymer and 40% sodium thiocyanate (NaSCN), and the spin dope was spun into aqueous solutions of NaSCN. In the melt-spinning experiment, polystyrene was used. The variables investigated were: size and shape of the spinnerette hole, coagulating bath concentration, throughput rate, and jet stretch. It has been found in wet spinning that, for a given shape of spinnerette hole, the fiber shape is most strongly affected by jet stretch and relatively little by the bath concentration and throughput rate. Also determined in the wet-spinning experiment was the maximum jet stretch at which thread breakage occurs. It has been found that the maximum jet stretch decreases as bath concentration is increased.     

Effect of the drawing process on the wet spinning of polyacrylonitrile fibers in a system of dimethyl sulfoxide and water

The effect of the drawing process on the structural characteristics and mechanical properties of polyacrylonitrile (PAN) fibers was comparatively studied. The protofibers extruded from the spinneret were the initial phase of stretching, which involved the deformation of the primitive fiber with the concurrent orientation of the fibrils. Wet‐spun PAN fibers observed by scanning electron microscopy exhibited different cross‐sectional shapes as the draw ratio was varied. X‐ray diffraction results revealed that the crystalline orientation of PAN fibers increased with increasing draw ratio; these differences in the orientation behaviors were attributed to the various drawing mechanisms involved. The crystalline and amorphous orientations of the PAN fibers showed different features; at the same time, the tensile properties were strongly dependent on the draw ratio. However, the stream stretch ratio had most influence on the tensile strength and the orientation of PAN fibers for the selected process parameters. Electron spin resonance proved that the local morphology and segmental dynamics of the protofibers were due to a more heterogeneous environment caused by the sequence structure. Differential scanning calorimetry indicated that the size and shape of the exotherm and exoenergic reaction were strongly dependent on the morphology and physical changes occurring during fiber formation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1026–1037, 2007     

杂环芳香族聚酰胺纺丝原液孔口胀大效应的研究

采用摄影法研究了杂环芳香族聚酰胺纺丝原液的孔口胀大效应。结果表明:杂环芳香族聚酰胺纺丝原液在喷丝头挤出时会发生孔口胀大现象,在纺丝原液比浓对数黏数为4.20 dL/g,温度20～65℃,挤出压力0.25～0.45 MPa,喷丝孔长径比为1～7,滤布层数为1的条件下,纺丝原液的孔口胀大比为1.089 0～1.344 8;纺丝原液的孔口胀大比随着原液温度的上升、毛细管长径比的增大和滤布层数的增加呈逐渐减小趋势,随着聚合物相对分子质量的增大和挤出压力的增加呈逐渐增大趋势;纺丝原液的孔口胀大活化能随挤出压力的增加而增大。     

Dry‐jet‐wet spun polyurethane fibers. I. Optimization of the spinning parameters

This study examined the spinning of polyurethane‐based elastomeric fibers with the dry‐jet‐wet spinning method. The three important spinning variables that were chosen were the coagulation bath ratio (dimethylformamide/water), the bath temperature, and the stretch ratio. A three‐variable factorial design method, proposed by Box and Behnken, was used to optimize these process parameters. The spinning process was further fine‐tuned by the variation of the stretch ratio and the dope solid content. The effect of the dry‐jet length on the fiber properties was also studied. The tenacity and elastic recovery properties of the fibers were found to be optimum at a bath ratio (dimethylformamide/water) of 60 : 40, a bath temperature of 15°C, and a stretch ratio of 2.5. The density and sonic modulus were measured to determine the effect of varying the process variables on structural parameters such as the density and orientation. The surface morphological features, as revealed by scanning electron microscopy, were correlated to the fiber properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Investigating the jet stretch in the wet spinning of PAN fiber

The jet stretch of wet‐spun PAN fiber and its effects on the cross‐section shape and properties of fibers were investigated for the PAN‐DMSO‐H₂O system. Evidently, the spinning parameters, such as dope temperature, bath concentration, and bath temperature, influenced the jet stretch. Also, under uniform conditions, the postdrawing ratio changed as well as that of jet stretch. When coagulation temperature was 35°C simultaneously with bath concentration of 70%, jet stretch impacted obviously the cross‐section shapes of PAN fiber, but had little effect when the temperature was below 10°C or above 70°C. As the jet stretch ratio increased, the crystallinity, crystal size, sonic orientation, and mechanical properties of the as‐spun fiber changed rapidly to a major value for jet stretch ratio of 0.9 where the cross section of as‐spun fiber was circular. With further increasing of jet stretch ratio, the properties changed slightly but the fiber shape was not circular. The results indicated that appropriate jet stretch, under milder formation conditions in wet‐spinning, could result in the higher postdrawing ratio and circular profile of PAN fiber, which were helpful to produce round PAN precursor with minor titer and perfect properties for carbon fiber. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

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     

Investigation the jet stretch in PAN fiber dry‐jet wet spinning for PAN‐DMSO‐H2O system

The jet stretch of dry‐jet wet spun PAN fiber and its effects on the cross‐section shape of fibers were investigated for a PAN‐DMSO‐H₂O system. Clearly, the spinning parameters, such as dope temperature, bath concentration, bath temperature, and air gap, all influenced the jet stretch. Also, under uniform conditions, the postdrawing ratio as well as that of jet stretch changed. Under given conditions, as the bath temperature was below 30°C or above 45°C, jet stretch had little effect on the cross‐sectional shapes of PAN fiber. Within the temperature of 30–45°C, fiber's cross‐section shapes change obviously from round over an approximate circular shape into to an elliptical or a flat shape. The scope of jet stretch produced PAN fiber with circular cross‐section was bigger than that in wet spinning. These results indicated that appropriate air gap height, under milder formation conditions in dry‐jet wet spinning, could result in higher jet stretch and higher postdrawing ratio. The appropriate jet stretch and postdrawing ratio could result in circular profile of PAN fiber, which were helpful to produce round PAN precursor with finer size and better properties for carbon fiber. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009