Gel spinning of polyacrylonitrile fibers with medium molecular weight

A new gel‐spinning method was employed to prepare polyacrylonitrile (PAN) fibers from a PAN spinning solution with dimethylsulfoxide and water as a mixed solvent. Aging at 25 °C for 120 min brought the spinning solution to the sol–gel transition and a three‐dimensional gel formed before entering the coagulation bath. The as‐spun fibers from the solution at the sol–gel transition and in the gel state possess a circular cross‐section. Compared with dry‐jet wet‐spun fibers, the gel‐spun fibers have a more compact structure, fewer voids and better mechanical properties after a three‐stage drawing. Moreover, the gel‐spun fibers obtained from the extraction bath have a more homogeneous microstructure and better packed supermolecular structure. The physical properties of the extracted gel‐spun fibers are also better than those of coagulated gel‐spun fibers. Copyright © 2010 Society of Chemical Industry     

Processing,structure, and properties of gel spun PAN and PAN/CNT fibers and gel spun PAN based carbon fibers

Polyacrylonitrile (PAN) and PAN/carbon nanotube (PAN/CNT) fibers were manufactured through dry‐jet wet spinning and gel spinning. Fiber coagulation occurred in a solvent‐free or solvent/nonsolvent coagulation bath mixture with temperatures ranging from ?50 to 25°C. The effect of fiber processing conditions was studied to understand their effect on the as‐spun fiber cross‐sectional shape, as well as the as‐spun fiber morphology. Increased coagulation bath temperature and a higher concentration of solvent in the coagulation bath medium resulted in more circular fibers and smoother fiber surface. as‐spun fibers were then drawn to investigate the relationship between as‐spun fiber processing conditions and the drawn precursor fiber structure and mechanical properties. PAN precursor fiber tows were then stabilized and carbonized in a continuous process for the manufacture of PAN based carbon fibers. Carbon fibers with tensile strengths as high as 5.8 GPa and tensile modulus as high as 375 GPa were produced. The highest strength PAN based carbon fibers were manufactured from as‐spun fibers with an irregular cross‐sectional shape produced using a ?50°C methanol coagulation bath, and exhibited a 61% increase in carbon fiber tensile strength as compared to the carbon fibers manufactured with a circular cross‐section. POLYM. ENG. SCI., 55:2603–2614, 2015. © 2015 Society of Plastics Engineers     

Structure and properties of partially cyclized polyacrylonitrile‐based carbon fiber—precursor fiber prepared by melt‐spun with ionic liquid as the medium of processing

Carbon fiber has many excellent properties. Currently, the precursor fiber of polyacrylonitrile (PAN)‐based carbon fiber is made from solution by wet or dry spinning process that requires expensive solvents and costly solvent recovery. To solve this problem, we developed a melt‐spun process with ionic liquid as the medium of processing. The melt‐spun precursor fiber exhibited partially cyclized structure. The structure and properties of the melt‐spun PAN precursor fiber were analyzed by combination of scanning electron microscope, Fourier transform infrared spectroscopy, differential scanning calorimetry, X‐ray diffraction, thermogravimetry, ultraviolet spectroscopy, flotation technique, sound velocity orientation test, linear density, and tensile strength tests. The results showed that the tensile strength of melt‐spun PAN precursor fiber was fairly high reached up to 7.0 cN/dtex. The reason was the low imperfect morphology and a cyclized structure formed by in situ chemical reaction during melt‐spun process. Due to the existence of partially cyclized structure in the melt‐spun PAN precursor fiber, exothermic process was mitigated and the heat evolved decreased during thermal stabilization stage in comparison with commercial precursor fibers produced by solution‐spun, which could shorten the residence time of thermal stabilization and reduce the cost of final carbon fiber. POLYM. ENG. SCI., 55:2722–2728, 2015. © 2015 Society of Plastics Engineers     

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     

Effects of different coagulation conditions on polyacrylonitrile fibers wet spun in a system of dimethylsulphoxide and water

Polyacrylonitrile (PAN) precursors were prepared by the wet spinning way. The effects of the coagulation conditions, such as coagulation temperature, coagulation ratio, and coagulation concentration, are discussed in detail. While keeping the coagulation bath concentration constant, as the coagulation bath temperature increased, the cross section deviated less from a circular form, and the as‐spun fiber diameter decreased. Measurement to the rate of the boundary movement has been calculated depending on the coagulation rate. While keeping the coagulation bath temperature constant, high coagulation bath concentration can cause more coagulant to diffuse into the solution to the polymer precipitated consequently, which led to a faster coagulation rate. The as‐spun fiber from high coagulation concentration was compacted than those from low concentration. The character of the formed structure reflected the system mobility and capability to crystallize. Improvement in fiber density in the as‐spun fiber resulted in improvements in the tensile strength of the as‐spun fiber. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3723–3729, 2007     

Effect of dry/wet spinning on the photooxidative degradation of acrylic fibers

The photooxidative degradation of acrylic fibers was investigated with two different fiber‐spinning processes, that is, dry spinning and wet spinning. Several analytical methods were used in this study: viscometry, X‐ray diffraction, Fourier transform infrared spectroscopy, optical measurements, and mechanical testing. Viscometry was used to determine the molecular weight as a monitoring factor for degradation. X‐ray diagrams showed lower changes in the crystallinity of wet‐spun fibers during a weathering process by irradiation. The results from mechanical testing indicated that the tenacity of dry‐spun fibers had less deterioration than that of wet‐spun fibers. Degraded wet‐spun and dry‐spun fibers showed similar trends in optical and spectroscopy analysis. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Wet‐spun,photoinitiator‐modified polyacrylonitrile precursor fibers: UV‐assisted stabilization

The role of dilute concentrations (～1 wt %) of a photoinitiator, 4,4 ′ ‐bis(diethylamino)benzophenone, on the processability and properties of the resulting wet‐spun polyacrylonitrile (PAN) fibers are reported. Rheology measurements show no adverse effect on the viscosities of solutions by the addition of the photoinitiator. Fibers containing photoinitiator were successfully wet‐spun from PAN – DMSO solution. FTIR results prove that 4,4 ′ ‐bis(diethylamino)benzophenone was retained in the fibers after coagulation and post‐stretching. SEM micrographs show no deterioration of the post‐stretched fiber microstructure due to the presence of photoinitiator. Tensile testing results show a small reduction in the strain‐at‐break of post‐stretched fibers containing photoinitiator when compared with pure (control) PAN fibers. After UV treatment, fibers with 4,4 ′ ‐bis(diethylamino)benzophenone display a higher tensile modulus compared with the other sets. Wide‐angle X‐ray diffraction results show no significant decrease in interplanar spacing and size of the crystals within the fibers containing photoinitiator, but such fibers retain a higher extent of molecular orientation after being UV treated. Conversion indices were measured from the WAXD spectra and compared with conventional thermal stabilized fibers. This correlation confirms that the addition of 1 wt % photoinitiator to PAN followed by 5 min of UV treatment leads to a conversion index that is observed in control fibers after more than an hour, which could reduce the conventional thermo‐oxidative stabilization time significantly. These results indicate the potential of the dual stabilization route in generating precursor fibers with higher molecular orientation, and possibly reducing the thermo‐oxidation time during carbon fiber processing. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2494–2503, 2013     

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     

Characteristics of polyacrylonitrile solutions and fibers varied with the dissolution process in ionic liquid

The concentrated polyacrylonitrile (PAN) solutions were prepared with 1‐butyl‐3‐methylimidazolium chloride ([BMIM]Cl) as solvent by static state, stirring, and kneading. The steady and oscillatory shear tests were carried out to investigate the viscoelastic behaviors of the PAN/[BMIM]Cl solutions by rotational rheometer. It was found that the zero shear‐rate viscosity and relaxation time of the solution prepared by kneading were lowest and the non‐Newtonian index was largest among the solution. During kneading, the gelation temperature of the viscous and homogenous solution was at the lowest temperature 22.7°C among the all three solutions. Only the solutions prepared by stirring and kneading could be spun by dry‐jet wet spinning technology. The fiber processed with the solution prepared by kneading could be drawn with a higher draw ratio, showing the larger draw ability. The supramolecular structure and properties of the fibers were studied by synchrotron wide‐angle X‐ray diffraction (WAXD) technologies, dynamic mechanical analysis (DMA), and mechanical tests. All the results showed that the kneading is an efficient method for PAN fiber spinning with [BMIM]Cl as solvent. It lead to the investigation of the methods of preparation of PAN solution in [BMIM]Cl, which affect the homogeneity of the solutions and hence the resulting characteristics of PAN fibers. POLYM. ENG. SCI., 55:558–564, 2015. © 2014 Society of Plastics Engineers     

聚丙烯腈熔融纺丝技术进展

叙述了聚丙烯腈的结构特征，丙烯腈聚合物的增塑，增塑和非增塑聚丙烯腈熔融纺丝工艺和纤维性质。熔纺制得的聚丙烯腈纤维，适用于纺织、地毯以及用作碳纤维原丝。增塑熔融纺丝技术已达到相当高的水平，熔纺纤维的形态与普通聚丙烯腈纤维类似，但存在皮芯结构，芯部有微孔。制得的聚丙烯腈基碳纤维原丝，拉伸强度达５．５～６．６ｃＮ／ｄｔｅｘ，用这种原丝生产的碳纤维的拉伸强度约为３．６×１０３ＭＰａ，模量约为２．３３×１０５ＭＰａ，伸长率约为１．５％，可制得性能优良的航空航天用复合材料。非增塑熔融纺丝，采用特定的丙烯腈聚合物和纺丝条件，不添加任何增塑剂，用普通熔融纺丝机在１０００ｍ／ｍｉｎ或２０００ｍ／ｍｉｎ以上的速度纺丝，经拉伸可得强度２．２～１１ｃＮ／ｄｔｅｘ、伸长率５％～３０％和模量５５～２２２ｃＮ／ｄｔｅｘ的纤维。     

Fibers from soybean protein and poly(vinyl alcohol)

Bicomponent fibers were wet‐spun from soybean protein and poly(vinyl alcohol). The protein core of the spun bicomponent fiber was brittle and showed a high frequency of core breakage upon drawing. Our effort was then to study the soybean protein solution, with the aim of trying to understand the cause for fiber brittleness and to determine the optimum solution conditions for fiber spinning. The effects of alkali, urea, and sodium sulfite on the viscosity of the soybean protein solution were examined. The hydrolytic stability of the soybean protein solution was examined at various pH values at two temperatures (room temperature and 60°C). Both the viscosity and gel electrophoresis were used for this purpose. The degradation of the soybean protein and the existing microgels in the protein spinning solution were thought to be the causes for the poor fiber drawability. Extent of protein denaturation will also effect the fiber drawability. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 11–19, 1999     

Preparation of poly(lactic acid) fiber by dry–jet–wet spinning. II. Effect of process parameters on fiber properties

The dry–jet–wet spinning process was employed to spin poly(lactic acid)(PLA) fiber by the phase inversion technique using chloroform and methanol as solvent and nonsolvent, respectively, for PLA. The as spun fiber was subjected to two‐stage hot drawing to study the effect of various process parameters, such as take‐up speed, drawing temperature, and heat‐setting temperature on the fiber structural properties. The take‐up speed had a pronounced influence on the maximum draw ratio of the fiber. The optimum drawing temperature was observed to be 90°C to get a fiber with the tenacity of 0.6 GPa for the draw ratio of 8. The heat‐setting temperature had a pronounced effect on fiber properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3774–3780, 2006     

Effect of spinning conditions on the mechanical properties of polyacrylonitrile fibers modified with carbon nanotubes

Carbon nanotubes (CNTs) were used to modify polyacrylonitrile (PAN) polymer. The PAN/CNT composite fibers were spun from dimethylformamide solutions containing different types of CNTs. The effect of nanotube addition to the fiber precursor on the resulting mechanical properties is discussed. In this study, we examined the relationship of the rheological properties of PAN spinning solutions containing various types of CNTs and the tensile strength of the resulting PAN fibers. The presence of CNTs in the PAN spinning solution enhanced its deformability during the drawing stage. This effect resulted in a higher tensile strength in the fibers containing nanotubes, as compared to the pure fibers. The use of a three‐stage drawing process resulted in a significant increase in the tensile strength of PAN fibers modified with multiwalled nanotubes. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Structure and properties of cellulose fibers from ionic liquids

1‐Butyl‐3‐methylimidazolium chloride ([BMIM]Cl) was used as a solvent for cellulose, the rheological behavior of the cellulose/[BMIM]Cl solution was studied, and the fibers were spun with a dry‐jet–wet‐spinning process. In addition, the structure and properties of the prepared cellulose fibers were investigated and compared with those of lyocell fibers. The results showed that the cellulose/[BMIM]Cl solution was a typical shear‐thinning fluid, and the temperature had little influence on the apparent viscosity of the solution when the shear rate was higher than 100 s^?1. In addition, the prepared fibers had a cellulose II crystal structure just like that of lyocell fibers, and the orientation and crystallinity of the fibers increased with the draw ratio increasing, so the mechanical properties of the fibers improved. Fibers with a tenacity of 4.28cN/dtex and a modulus of 56.8 cN/dtex were prepared. Moreover, the fibers had a smooth surface as well as a round and compact structure, and the dyeing and antifibrillation properties of the fibers were similar to those of lyocell fibers; however, the color of these dyed fibers was brighter than that of lyocell fibers. Therefore, these fibers could be a new kind of environmentally friendly cellulose fiber following lyocell fibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation of poly(lactic acid) fiber by dry‐jet‐wet‐spinning. I. Influence of draw ratio on fiber properties

Poly(lactic acid) fiber was prepared by dry‐jet‐wet spinning of the polymer from chloroform solution and with methanol as the precipitating medium. The as‐spun fiber was subsequently made into high strength fiber by two‐step process of drawing at a temperature of 90°C and subsequent heat setting in the temperature range of 120°C. The draw ratio had significant influence on the crystallinity and the tensile strength of the fiber. The fiber with the tenacity of 0.6 GPa and modulus of 8.2 GPa was achieved at a draw ratio of 8. The differential scanning calorimetry revealed an increase in the glass‐transition temperature with the increase in the draw ratio, which suggests the orientation of chains during the drawing process. The surface morphology of the filament as revealed by scanning electron microscopy shows that fibers are porous in nature, but a significant reduction in the porosity and pore size of the fiber was observed with the increase in the draw ratio. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1239–1246, 2006     

Preparation and characterization of ultrafine electrospun polyacrylonitrile fibers and their subsequent pyrolysis to carbon fibers

The present contribution reports the fabrication and characterization of ultrafine polyacrylonitrile (PAN) fibers by electrospinning and further development of the as‐spun PAN fibers into ultrafine carbon fibers. The effects of solution conditions (i.e., solution concentration, viscosity, conductivity, and surface tension) and process parameters (i.e., applied electrostatic field strength, emitting electrode polarity, nozzle diameter, and take‐up speed of a rotating‐drum collector) on morphological appearance and average diameter of the as‐spun PAN fibers were investigated by optical scanning (OS) and scanning electron microscopy (SEM). The concentration, and hence the viscosity, of the spinning solutions significantly affected the morphology and diameters of the as‐spun PAN fibers. The applied electrostatic field strength and nozzle diameter slightly affected the diameters of the as‐spun fibers, while the emitting electrode polarity did not show any influence over the morphology and size of the as‐spun fibers. Utilization of the rotating‐drum collector enhanced the alignment of the as‐spun fibers. Within the investigated concentration range, the average diameter of the fibers ranged between 80 and 725 nm. Finally, heat treatment of the as‐spun fibers with their average diameter of about 450 nm was carried out at 230 and 1000 °C, respectively. Various characterization techniques revealed successful conversion into carbon fibers with an average diameter of about 250 nm. Copyright © 2006 Society of Chemical Industry     

拉伸对异形聚丙烯腈原丝截面形状的影响

研究了湿法和于湿法纺制异形聚丙烯腈(PAN)纤维过程中拉伸对纤维截面形状的影响。结果表明:喷丝头拉伸对湿法纺制的PAN初生纤维截面影响明显,随着喷丝头拉伸倍数的增大,纤维异形度逐渐增大;喷丝头拉伸对于湿法纺制的纤维截面形状和异形度影响较小;沸水拉伸对二者的纤维截面形状和异形度几乎无影响。     

High resolution transmission electron microscopy study on polyacrylonitrile/carbon nanotube based carbon fibers and the effect of structure development on the thermal and electrical conductivities

Polyacrylonitrile (PAN) and PAN/carbon nanotube (CNT) based carbon fibers at various CNT content have been processed and their structural development was investigated using high resolution transmission electron microscope (HR-TEM). In CNT containing carbon fibers, the CNTs act as templating agents for the graphitic carbon structure development in their vicinity at the carbonization temperature of 1450 °C, which is far below the graphitization temperature of PAN based carbon fiber (>2200 °C). The addition of 1 wt% CNT in the gel spun precursor fiber results in carbon fibers with a 68% higher thermal conductivity when compared to the control gel spun PAN based carbon fiber, and a 103% and 146% increase over commercially available IM7 and T300 carbon fibers, respectively. The electrical conductivity of the gel spun PAN/CNT based carbon fibers also showed improvement over the investigated commercially available carbon fibers. Increases in thermal and electrical conductivities are attributed to the formation of the highly ordered graphitic structure observed in the HR-TEM images. Direct observation of the graphitic structure, along with improved transport properties in the PAN/CNT based carbon fiber suggest new applications for these materials.     

碳纳米管/聚丙烯腈复合纤维的制备及结构研究

通过原位聚合的方法制备了碳纳米管/聚丙烯腈(CNTs/PAN)聚合液,用湿法纺丝工艺制备了CNTs/PAN复合纤维,分析了复合纤维流变性能、热性能及截面形貌。结果表明:CNTs的加入使得聚合物溶液出现了假凝胶化,粘度和弹性均有所上升,纺丝时溶液细流的表层遇水迅速凝固成致密的皮层,影响了纤维芯部的二甲基亚砜(DMSO)和水的双扩散作用,凝固丝出现了很明显的皮芯结构,CNTs的加入还使得纤维预氧化放热过程得到了缓和。     

Impact of the wet spinning parameters on the alpaca-based polyacrylonitrile composite fibers: Morphology and enhanced mechanical properties study

The study examined the effect of different wet spinning parameters (e.g., total solid content, coagulation bath concentration, drawing, and stretching) on the morphology and mechanical properties of the wet spun alpaca/polyacrylonitrile (PAN) composite fibers. The alpaca/PAN composite fibers were wet spun using 10, 20, and 30% of alpaca particles along with the PAN polymer. The shear-thinning or non-Newtonian flow behavior was observed among the dope solutions with different solid content. The cross-sectional fiber morphology showed the bean-shaped characteristic for the control PAN fibers, whereas the alpaca/PAN composite fibers exhibited almost circular shape. “Cavity healing” was observed, where noticeable voids and porous areas were demolished in the cross section of the composite fibers, by changing the total solid content and coagulation bath concentration. Although the control PAN fibers exhibited the highest tenacity with lower fiber diameter, the alpaca/PAN composite fibers showed a gradual deterioration in tenacity while adding alpaca particles into the PAN polymeric matrix. Nevertheless, due to the increment in the total solid content, higher draw ratio, and stretching of the fibers, the tenacity, molecular orientation, and the crystallinity of the composite fibers were increased.