Lyocell fibers as the precursor of carbon fibers

In this work, Lyocell fibers, used as carbon fiber precursors, were investigated. Lyocell fibers used for the carbon precursors and the carbon fibers themselves were produced in our laboratory. The mechanical properties morphology and structure of the precursors and the obtained carbon fibers were studied and compared to those of rayon. The results show that Lyocell fibers have higher tenacity and modulus, and better thermal stability than rayon fibers. Scanning electron microscopy (SEM) experiments show that Lyocell precursors have round cross‐sections and fewer defects in the fibers, while rayon fiber has an oval cross‐section and many defects. Wide angle X‐ray diffraction (WAXD) results for the Lyocell precursors indicate that the degree of crystallinity of the Lyocell precursor is higher than that of a rayon precursor. They also show that Lyocell based carbon fibers have better mechanical properties than those that are rayon‐based. WAXD data of the obtained carbon fibers show that the crystallinity of Lyocell‐based carbon fiber is higher than that of rayon‐based carbon fiber. It is concluded that the Lyocell fibers are better precursors for carbon fibers than rayon. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1941–1947, 2003     

Potential of producing carbon fiber from biorefinery corn stover lignin with high ash content

The possibility of producing carbon fiber from an industrial corn stover lignin was investigated in the present study. As‐received, high‐ash containing lignin was subjected to methanol fractionation, acetylation, and thermal treatment prior to melt spinning and the changes in physiochemical and thermal properties were evaluated. Methanol fractionation removed most of the impurities in the raw lignin and also selectively removed the molecules with high melting points. However, neither methanol fractionation nor thermal treatment rendered melt‐spinnable precursors. The precursors were highly viscous and decomposed easily at low temperatures, attributed to the presence of H, G phenolic units, and abundant hydroxycinnamate groups in herbaceous lignin. A two‐step acetylation of methanol fractionated lignin greatly improved the mobility of lignin, while enhancing the thermal stability of the precursor during melt‐spinning. Fourier Transform Infrared and 2D‐NMR analysis showed that the contents of phenolic and aliphatic hydroxyls, as well as the hydroxycinnamates, decreased in the acetylated precursors. The optimum precursor was a partially acetylated lignin with a glass transition temperature of 85 °C. Upon oxidative stabilization and carbonization, the carbon fibers with an average tensile strength of 454 MPa and modulus of 62 GPa were obtained. The Raman spectroscopy showed the I_D/I_G ratio of the carbon fiber was 2.53. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45736.     

Carbon nanofibers from renewable bioresources (lignin) and a recycled commodity polymer [poly(ethylene terephthalate)]

Utilizing inexpensive biorenewable and waste raw materials for the production of carbon nanofibers can pave the way for lowering their manufacturing cost. In this research, lignin is combined with recycled poly(ethylene terephthalate) (PET) to fabricate precursor fibers via electrospinning. The process is optimized using the Design of Experiments statistical methodology and fibers with minimum average diameter equal to 191 ± 60 nm are prepared. Investigation with Attenuated Total Reflection – Fourier Transform Infrared Spectroscopy reveals the lignin structural changes induced by the solvent (trifluoroacetic acid), which is used for the preparation of homogeneous solutions of lignin and PET in various concentrations, while it gives an indication of the blending of the two electrospun polymers. The good miscibility between lignin and PET is also confirmed with Differential Scanning Calorimetry. The subsequent carbonization of the precursor fibrous mats results in a fibrous carbon structure with average fiber diameters similar to those of the precursor fibers. The successful transformation into carbon nanofibers is affirmed by Energy Dispersive X‐ray Spectroscopy. The Carbon content of these nanofibers amounts to 94.3%. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43936.     

Producing high‐quality precursor polymer and fibers to achieve theoretical strength in carbon fibers: A review

The precursor fiber quality has a large impact on carbon fiber processing in terms of its performance, production yield, and cost. Polyacrylonitrile precursor fibers have been used commercially to produce strong carbon fibers with average tensile strength of 6.6 GPa. There is a scope to improve the average tensile strength of carbon fibers, since only 10% of their theoretical strength has been achieved thus far. Most attempts to increase the tensile strength of carbon fibers have been made during the conversion of precursor fiber to carbon fiber. This review highlights the potential opportunities to enhance the quality of the polyacrylonitrile‐based precursor fiber during polymer synthesis, spinning, and postspinning. These high‐quality precursor fibers can lead to new generation carbon fibers with improved tensile strength for high‐performance applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43963.     

A new modification method of exploded lignin for the preparation of a carbon fiber precursor

A lignin-pitch for carbon fiber was prepared in a high yield from exploded lignin on phenolysis followed by heat treatment under a vacuum. The lignin-pitch had an excellent spinnability in the melt state to form a fine filament. The green fibers were easily made infusible when heated in air at a relatively high heating rate (15-60°C/h). The lignin-based carbon fiber was produced in 43.7% of yield based on a starting material. The tensile strength was more than 400 MPa, indicating that the lignin-based carbon fiber is classified into a general purpose grade. © 1993 John Wiley & Sons, Inc.     

Melt‐electrospinning of poly(ethylene terephthalate) and polyalirate

Rodlike polymer samples were made from three kinds of poly(ethylene terephthalate) (PET) pellets with different intrinsic viscosities (IV), and from polyalirate (Vectra) pellets. PET and Vectra fibers were produced using a melt‐electrospinning system equipped with a CO₂‐laser melting device from these rodlike samples. The effects of IV value and laser output power on the fiber diameter of PET were investigated. Furthermore, the effect of the laser output power on the fiber diameter of Vectra was investigated. The crystal orientation of these produced fibers was also investigated by X‐ray photographs. The following conclusions were reached: (i) the diameter of PET fiber decreases with increasing laser output power; (ii) the minimum average diameter of PET fibers is scarcely influenced by the value of IV; (iii) the electrospun PET fibers show isotropic crystal orientation; (iv) fibers having an average fiber diameter smaller than 1 μm cannot be obtained from PET and Vectra using the system developed; and (v) preferred liquid crystal orientation can be seen in electrospun Vectra fibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Lignin-based carbon fibers for composite fiber applications

Carbon fibers have been produced for the first time from a commercially available kraft lignin, without any chemical modification, by thermal spinning followed by carbonization. A fusible lignin with excellent spinnability to form a fine filament was produced with a thermal pretreatment under vacuum. Blending the lignin with poly(ethylene oxide) (PEO) further facilitated fiber spinning, but at PEO levels greater than 5%, the blends could not be stabilized without the individual fibers fusing together. Carbon fibers produced had an over-all yield of 45%. The tensile strength and modulus increased with decreasing fiber diameter, and are comparable to those of much smaller diameter carbon fibers produced from phenolated exploded lignins. In view of the mechanical properties, tensile 400–550 MPa and modulus 30–60 GPa, kraft lignin should be further investigated as a precursor for general grade carbon fibers.     

再生涤纶超短纤维的保温性能研究

系统研究了不同形貌结构的再生涤纶的保温效率。研究表明:线密度为0.8 dtex的再生涤纶的直径为12~14μm,线密度为1 dtex的再生涤纶中空纤维的直径为13~20μm,中空再生涤纶的直径分布较宽,而非中空纤维的纤维直径分布更窄;在相同线密度下,开松后纤维的保温率比未开松纤维的高;在切断长度相同的情况下,线密度越高,相同填充量下纤维的保温性能越差;保温填充材料越少,填充切断长度越短的纤维,越有利于保温性能的提升,而纤维长度越长,填充材料越多的保温效率也更高;在相同填充量情况下,中空纤维比非中空纤维具有更高的保温率;此外,开松后的纤维具有更优良的保温效果,且保温材料填充量达到80 g左右时,充填量基本达到饱和,继续添加试样,会造成纤维之间互相挤压,反而对保温效果不利。     

Carbon fibers from dry-spinning of acetylated softwood kraft lignin

An acetylated softwood kraft lignin was dry-spun into precursor fibers and successfully processed into carbon fibers with a tensile strength exceeding most values reported in prior studies on lignin-based carbon fibers. Limited acetylation of lignin hydroxyl groups enabled dry-spinning of the precursor using acetone (solvent) followed by thermo-oxidative stabilization. Resulting carbon fibers (∼7 μm diameter) displayed a tensile modulus, strength, and strain-to-failure values of 52 ± 2 GPa, 1.04 ± 0.10 GPa, and 2.0 ± 0.2%, respectively. Because of solvent diffusion during dry-spinning, fibers displayed a crenulated surface that can provide a larger specific interfacial area for enhanced fiber/matrix bonding in composite applications.     

Characterization of polyacrylonitrile,poly(acrylonitrile‐co‐vinyl acetate), and poly(acrylonitrile‐co‐itaconic acid) based activated carbon nanofibers

In this study, three different acrylonitrile (AN)‐based polymers, including polyacrylonitrile (PAN), poly(acrylonitrile‐co‐vinyl acetate) [P(AN‐co‐VAc)], and poly(acrylonitrile‐co‐itaconic acid) [P(AN‐co‐IA)], were used as precursors to synthesize activated carbon nanofibers (ACNFs). An electrospinning method was used to produce nanofibers. Oxidative stabilization, carbonization, and finally, activation through a specific heating regimen were applied to the electrospun fibers to produce ACNFs. Stabilization, carbonization, and activation were carried out at 230, 600, and 750 °C, respectively. Scanning electron microscopy, thermogravimetric analysis (TGA), and porosimetry were used to characterize the fibers in each step. According to the fiber diameter variation measurements, the pore extension procedure overcame the shrinkage of the fibers with copolymer precursors. However, the shrinkage process dominated the scene for the PAN homopolymer, and this led to an increase in the fiber diameter. The 328 m²/g Brunauer–Emmett–Teller surface area for ACNFs with PAN precursor were augmented to 614 and 564 m²/g for P(AN‐co‐VAc) and P(AN‐co‐IA), respectively. The TGA results show that the P(AN‐co‐IA)‐based ACNFs exhibited a higher thermal durability in comparison to the fibers of PAN and P(AN‐co‐VAc). The application of these copolymers instead of AN homopolymer enhanced the thermal stability and increased the surface area of the ACNFs even in low‐temperature carbonization and activation processes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44381.     

Morphological evolution of boron carbide particles: Sol-gel synthesis of nano/micro B4C fibers

Herein we present a novel non-catalytic sol-gel route to synthesize nano/micro boron carbide fibers. By in-situ decoration of the precursor surface with boric acid crystals during the thermal decomposition stage, the growth kinetics of boron carbide particles was manipulated. Therefore, the formation of anisotropic crystals instead of polyhedral-equiaxed ones was successfully enabled. The results indicated that highly crystalline boron carbide (B₄C) particles with a low amount (<1 ± 5 wt%) of free carbon were obtained. The SEM and HR-FESEM micrographs revealed that B₄C particles with fully polyhedral-equiaxed morphology were obtained from the precursors, which were thermally decomposed with 2 h holding time at 675 °C. As a result of increased thermal decomposition duration of precursor, B₄C particles with various morphologies, such as rhomboid-plate, nanobelt, and fiber were formed beside the polyhedral-equiaxed particles. The yield of boron carbide fiber formation was increased, and polyhedral-equiaxed particles were decreased in the final products by tailoring the structure of the preceramic precursor. The products containing at least 50% of boron carbide fiber were achieved using 12 h of thermally decomposed precursors. The formation and growth mechanisms of boron carbide particles were speculated and comprehensively discussed.     

Structural changes during the thermal stabilization of modified and original polyacrylonitrile precursors

A polyacrylonitrile (PAN) precursor fiber of a special grade for preparing carbon fibers was modified by the impregnation of an aqueous KMnO₄ solution. The effects of the modification on the lateral and morphology structure, related to the crystalline properties of both the precursors and preoxidized fibers, such as the orientation index, crystal size, and crystallinity index, were measured by wide‐angle X‐ray diffraction. For both modified and original PAN fibers, a comparative study of the changes of the elemental content during the process of preoxidation, the relations between the thermal stress and heat‐treatment temperature, and the effect of the modification on the skin/core structure of a preoxidized fiber were also introduced by the use of elemental analysis, optical microscopy, and so on. The modification of KMnO₄ was demonstrated to increase the density, increase the crystallinity index, increase the preferred orientation index, and decrease the crystal size for a modified precursor fiber and for a preoxidized fiber developed from a modified precursor fiber after a different heat‐treatment temperature. KMnO₄ also showed a catalytic action, accelerating the rate of preoxidation and reducing the time of thermal stabilization; this improved the homogenization of the cross‐section structure and led to an improvement in the tensile strength of 15–20% and an improvement in the elongation of 20–30% in the resulting carbon fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2047–2053, 2005     

木质素基低成本碳纤维的研究现状

从木质素基碳纤维的制备方法、力学性能、结构特征及力学性能的影响因素等几个方面,阐述了当前木质素基碳纤维的研究现状,并对今后的研究方向提出了几点建议,以期能为木质素基碳纤维的研究工作提供一定的参考。     

Lyocell纤维原丝的性能对碳纤维强度的关联分析

运用灰色系统方法对新型纤维素原丝Lyocell纤维的性能与碳纤维强度之间的关系进行了关联分析，结果表明：Lyocell纤维的强度、纤度和断裂强力对碳纤维的强度有很大的影响，而对伸长和模量的影响较小。     

Lignin‐based carbon fibers: Accelerated stabilization of lignin fibers in the presence of hydrogen chloride

Organosolv switchgrass lignin (SGL) and hardwood lignin (HWL) polymers are used as precursors to prepare low cost carbon fibers (CFs). Lignin powder and fiber samples are stabilized and carbonized at different conditions to investigate the effect of HCl on thermal‐oxidative stabilization time, mass yield, fiber diameter, and mechanical properties. The results show that HCl can accelerate stabilization and reduce the stabilization time from many hours to 75 min for the SGL fibers, and to 35 min for the HWL fiber. The rate of rapid stabilization in HCl/air is at least four times faster than conventional stabilization in air. The CFs prepared with two different stabilization methods have almost the same strength and modulus, but higher carbon yield is obtained with the rapid stabilization due to a short time of oxidation. Pores and defects observed on the surface and the cross‐section of the CFs across all stabilization conditions contribute to low fiber strength. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45507.     

Nano‐carbon black filled Lyocell fiber as a precursor for carbon fiber

In this work, Lyocell fibers filled with various amounts of carbon black were prepared. Wide angle X‐ray diffraction (WAXD) results showed that carbon black filled Lyocell fibers still had a cellulose II crystal structure and kept the characteristic peak of carbon black at the same time. The results of mechanical properties showed a slight reduction in the carbon black filled Lyocell fiber. Moreover, the heat stabilities of the carbon black filled Lyocell fibers showed no obvious change. The residue of carbon black filled Lyocell fiber at 1000°C was higher than that of Lyocell fiber, implying higher carbon yield could be obtained for the carbon black filled Lyocell precursor. Scanning electron microscopy (SEM) experiments showed that the surface and the cross section of carbon black filled Lyocell fiber were smooth and round, which are consistent with the carbon fiber precursor. The WAXD pattern of carbon black filled Lyocell‐based carbon fiber was different from that of Lyocell‐based carbon fiber. The addition of carbon black transfers the diffraction peak of carbon fiber while keeping the characteristic structure of carbon black. The results of mechanical properties of carbon fibers show that, if an appropriate amount of carbon black was chosen, carbon fiber with better properties than Lyocell‐based carbon fiber could be obtained by using the carbon black filled Lyocell fibers as the precursor. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 65–74, 2006     

Characteristics of wet‐spun and thermally treated poly acrylonitrile fibers

The performance of carbon fibers depends on the quality of the precursor and the conditions of the thermal treatment. In detail, for a PAN precursor fiber the viscosity of a spinning dope and the draw ratio during the spinning process needs to be considered. Through wet spinning, different types of PAN precursor fibers with defined spinning parameters, including solid content, solvent content in a bath, and especially draw ratio resulting in defined cross section diameters, were fabricated and analyzed with tensile tests, density investigations, SEM, TGA‐MS, FTIR, and XRD. The results show that the mechanical properties of the fibers correlate to crystallinity. The cross section diameter is strongly related to the morphology of the fibers after thermal treatment. By extending the postdrawing of PAN fibers high tenacities were obtained at the cost of the cross section shape. In addition, TGA measurements reveal trapped residues of the wet spinning process as well as show several chemical reactions takes place at the same time at different temperatures. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43698.     

不同线密度粘胶原丝及其碳纤维的结构性能对比

用Weibull分析处理 10mm长的 4种不同线密度粘胶原丝和相应碳纤维的单丝断裂强度 ,得到原丝线密度、强度分布和碳纤维强度的对应关系。采用透射电镜 (TEM )和小角X散射 (SAXS)分析粗旦原丝 ,发现孔洞较多 ,并存在大于 70nm的大孔洞。截面和表面照片也揭示出细旦原丝截面相对规整 ,表面较光滑 ,粗旦原丝则反之。结果表明 ,原丝线密度小 ,截面形状圆整 ,缺陷少 ,所制得的碳纤维强度高。     

Mass production of carbon nanotube‐reinforced polyacrylonitrile fine composite fibers

A facile and large‐scale production method of polyacrylonitrile (PAN) fibers and carboxyl functionalized carbon nanotube reinforced PAN composite fibers was demonstrated by the use of Forcespinning® technology. The developed polymeric fibers and carbon nanotube‐reinforced composite fibers were subsequently carbonized to obtain carbon fiber systems. Analysis of the fiber diameter, homogeneity, alignment of carbon nanotube and bead formation was conducted with scanning electron microscopy. Thermogravimetric analysis, electrical, and mechanical characterization were also conducted. Raman and FTIR analyses of the developed fiber systems indicate interactions between carbon nanotubes and the carbonized PAN fibers through π–π stacking. The carbonized carbon nanotube‐reinforced PAN composite fibers possess promising applications in energy storage applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40302.     

超细碳纤维毡的制备及其形貌研究

采用静电纺丝法制备了聚酰胺酸（PAA）无纺布纤维毡,通过亚胺化工艺得到聚酰亚胺（PI）纤维毡,再以PI纤维毡为前驱体经高温碳化工艺制备PI基超细碳纤维毡,并对制得的PI基超细碳纤维毡进行了扫描电镜（SEM）形貌分析和元素分析。经SEM分析得知,随着碳化温度的升高碳纤维毡中纤维的直径逐渐减小,其分布略变窄,主要分布在200-300nm之间,当碳化温度达到1000℃时,PI基超细碳纤维毡中纤维的碳含量为96.16％。