Carbon Fiber Precursor Research Articles

Kinetics of the cyclization and isomerization reactions in polyacrylonitrile based carbon fiber precursors during thermal‐oxidative stabilization

ABSTRACTThe kinetics of reactions in polyacrylonitrile (PAN) based carbon fiber (CF) production should be of significance to the guidance of process control, fiber structure formation. PAN precursor fibers were isothermally stabilized at 210, 225, 240, 255, and 270 °C, respectively, for 10 to 100 min in an air oven to study the kinetics of the cyclization and isomerization reactions. The structural evolution of PAN precursor fibers during thermal‐oxidative stabilization was characterized by Fourier transform infrared (FTIR) spectroscopy and solid state 13C nuclear magnetic resonance (13C NMR). The results indicate that the FTIR absorbance of CN (the resultant of the cyclization) in PAN shows a trend of first increasing and then decreasing. And then the NMR peak assigned to the carbon atoms linking imino groups (NH) proves the isomerization of CN into NH in pyridone structure. Based upon the FTIR absorbance method, the entire process of the cyclization and isomerization reactions is considered as a consecutive first‐order reaction. A kinetic model for the consecutive reaction has been established via the evaluation of the reaction rate constants of two single reactions. According to the model, the simulated kinetic curves of the characteristic groups (CN, CN, and NH) conform to the FTIR absorbance trends of these groups based on experimental data. This study is expected to furnish in‐depth information on the crucial reaction kinetics during stabilization of PAN precursors, which is of advantage to the process optimization of the CF production. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48819.

Accelerating Thermal Stabilization by Pyrolytic Lignin for Partially Bio‐Based Carbon Fiber Precursor

AbstractIn this study, a partially bio‐based carbon fiber (CF) precursor is prepared by blending 32 wt% of pyrolytic lignin (PyL) with 68 wt% of poly(acrylonitrile‐co‐itaconic acid) (PANIA), and the effect of PyL on forming conjugated ladder structure during stepwise thermal stabilization is studied. The results of X‐ray photoelectron spectroscopy (XPS) reveal that PyL accelerates the formation of conjugated ladder structure at 230 °C during thermal stabilization for PANIA/PyL, which is 15 °C lower and 13 min earlier than PANIA. The acceleration on forming thermally stable conjugated ladder structure can be confirmed through Fourier‐transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Moreover, the fiber stabilized at 230 °C is subsequently made into PANIA/PyL‐230 CF, which has relatively higher‐ordered graphitic structure and dense morphology without voids. The mechanism of PyL accelerating the formation of conjugated ladder structure during thermal stabilization is discussed.

Predicting cost-effective carbon fiber precursors: Unraveling the functionalities of oxygen and nitrogen-containing groups during carbonization from ReaxFF simulations

Blends of polyacrylonitrile (PAN) and poly(p-phenylene-2,6-benzobisoxazole) (PBO) as precursors may offer an opportunity to reduce the cost of carbon fiber (CF) production. The all-carbon ring formations and volatile gas production during the heating and carbonization for 9 PAN/PBO blend precursors with varying mixing ratios are studied via the ReaxFF reactive molecular dynamics simulations. Evolutions of oxygen-containing (O-containing) and nitrogen-containing (N-containing) groups are detailed, in order to reveal the reaction mechanisms of the O and N-based CF precursors. Particularly, the O-containing groups are identified to be more efficient for initiating the carbonization, whereas N-containing groups are far longer retained in the graphitic materials and play a key role in capturing and converting carbon radical species into the graphitic networks. Additionally, the PAN/PBO blend precursor with a mole ratio of 1:1 is compared with the pre-oxidized PAN, PAN, and PBO. It is found that the PAN/PBO blends could be a promising alternative for the cost-effective PAN-based CF precursors, since they can decrease the cost of the CF production by means of: (a) eliminating the pre-oxidation process, (b) having considerable all-carbon ring formations within a short period, and (c) having a relatively fast conversion rate, reaching 95% 6-membered carbon ring formation.

Synthesis and Processing of Melt Spun Materials from Esterified Lignin with Lactic Acid

In this study, the carbon fiber manufacturing process is investigated, using high-density polyethylene (HDPE) and esterified lignin either with lactic acid (LA) or with poly(lactic acid) (PLA) as precursors. More specifically, lignin was modified using either LA or PLA in order to increase its chemical affinity with HDPE. The modified compounds were continuously melt spun to fibrous materials by blending with HDPE in order to fabricate a carbon fiber precursor. The obtained products were characterized with respect to their morphology, as well as their structure and chemical composition. Moreover, an assessment of both physical and structural transformations after modification of lignin with LA and PLA was performed in order to evaluate the spinning ability of the composite fibers, as well as the thermal processing to carbon fibers. This bottom–up approach seems to be able to provide a viable route considering large scale production in order to transform lignin in value-added product. Tensile tests revealed that the chemical lignin modification allowed an enhancement in its spinning ability due to its compatibility improvement with the commercial low-cost and thermoplastic HDPE polymer. Finally, stabilization and carbonization thermal processing was performed in order to obtain carbon fibers.

High molecular weight poly(acrylonitrile-co-3-aminocarbonyl-3-butenoic acid methyl ester) prepared by mixed solvent polymerization I. effect of monomer feed ratios on polymerization and stabilization

In order to improve the pre-oxidation performance and molecular weight of polyacrylonitrile (PAN). In this work, 3-aminocarbonyl-3-butenoic acid methyl ester) (ABM) was used as comonomers to formulate high molecular weight poly(acrylonitrile-co-3-amino-carbonyl-3-butenoic acid methyl ester) [P(AN-co-ABM)] copolymer by radical polymerization in the mixed solvent of dimethyl sulfoxide/deionized water =60/40 (wt/wt). The highest molecular weight of resultant P(AN-co-ABM) is 4.87 × 105 g/mol, 5 times larger than that prepared by solution polymerization under the same reaction conditions. The monomer reactivity ratios are calculated by Fineman-Ross and Kelen-Tudos methods based on the elemental analysis results. Thermal properties of P(AN-co-ABM) copolymer with different monomer feed ratios were studied by Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry in detail. The results show that the stabilization of P(AN-co-ABM) has been significantly improved by ABM, confirmed by the lower initiation temperature and broader exothermic peak in DSC curves, larger extent of stabilization from FTIR and XRD studies, and smaller Ea of cyclization, which is due to the initiation of ABM through ionic mechanism. This study clearly shows that high molecular weight P(AN-co-ABM) copolymer is a better material for carbon fiber precursor.

Impact of PEO structure and formulation on the properties of a Lignin/PEO blend

To improve the performance of lignin/PEO fibers as precursors of carbon fibers, blend formulations were designed with an epoxidized PEO and with carbon nanotubes. Model studies demonstrated that the epoxidized PEO could covalently link to lignin. With incorporation of epoxidized PEO, the precursor fibers exhibited enhanced degree of crystallinity of 70 % (52 % without epoxidized PEO) and a doubling of their young modulus (from 200 to 450 MPa) and tensile strength (from 6 to 12 MPa). In contrast, the addition of carbon nanotubes did not impact the morphology nor the mechanical performance of the resulting fibers. It is argued that with its ability to couple lignin to the PEO matrix, epoxidized PEO plays the role of a stress transfer agent between the rigid lignin regions and the flexible PEO regions, thereby improving the blend performance.

New, innovative 80K tow carbon fiber precursor for non-aerospace use to hit the market in mid-2020

Reinforced PlasticsVol. 64, No. 3 FeatureNew, innovative 80K tow carbon fiber precursor for non-aerospace use to hit the market in mid-2020Joan Miquel JoaquimJoan Miquel JoaquimMiranda de Ebro, SpainSearch for more papers by this authorJoan Miquel JoaquimPublished Online:7 Nov 2021https://doi.org/10.1016/j.repl.2019.10.005AboutSectionsView articleView Full TextPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareShare onFacebookTwitterLinked InEmail View article FiguresReferencesRelatedDetails 1 June 2020Volume 64Issue 3ISSN (print): 0034-3617ISSN (online): 1873-1694 Metrics History Published online 7 November 2021 Published in print 1 June 2020 Information© MA Business Ltd.PDF download

Wet-spinning of Cellulose Acetate Reinforced with Acetylated Nano-crystalline Cellulose as Carbon Fibre Precursors

The search precursors that are bio-based, renewable and biodegradable has attracted significant attention due to increased environmental awareness. Recently, nano-crystalline cellulose (NCC) has been considered as a potential precursor to produce carbon fibre owing to its high crystallinity and excellent mechanical properties. However, its crystallinity prevents it from being dissolved in comment solvents. The main aims of this study were: (i) to acetylate NCC to improve its compatibility with cellulose acetate and (ii) to produce wet-spun cellulose acetate fibres reinforced acetylated and unacetylated NCC. In this study, rod-like particles of NCC with diameters in the range 2.0-4.8 nm and lengths of 46-114 nm were characterised using a Transmission Electron Microscope (TEM). The carbonyl (C=O) group of the acetyl group was confirmed using Fourier Transmission Infrared (FTIR), and the crystallinity of NCC was characterised using X-Ray Diffraction (XRD). The crystallinity indicates of the NCC before and after acetylation were 78% and 68% respectively. The morphology of wet-spun cellulose acetate reinforced acetylated NCC was smoother than reinforced NCC. The acetylation on NCC increased its compatibility with the polymer matrix.

Wet‐Spinning and Carbonization of Lignin‐Polyvinyl Alcohol Precursor Fibers

AbstractLignin is a promising bio‐based precursor for sustainable carbon fibers. Limiting factors for their development include the brittleness of lignin and the lack of large‐scale production routes. Here, a simple and economic wet‐spinning method, suitable for the fabrication of fibers based on softwood Kraft lignin (KL) and polyvinyl alcohol (PVA), is proposed. These two polymers reveal a partial miscibility in solution, and form metastable dispersions in solid state. KL‐PVA fibers are prepared at a weight ratio of 70:30 and are carbonized without thermo‐stabilization. A tailor‐made temperature program leads to a decreased microporosity on the fiber surfaces. The obtained carbon structures at 1000 °C are found to be poorly ordered, leading to only intermediate mechanical and electrical properties. However, graphitic domains appear at temperatures above 1500 °C and indicate a high potential for the system.

Polyacrylonitrile/liquid crystalline graphene oxide composite fibers – Towards high performance carbon fiber precursors

We have prepared high performance, continuous carbon fiber precursors mimicking the industrial processing by wet spinning technology using polyacrylonitrile (PAN)/liquid crystalline graphene oxide (LCGO) for the first time. This work highlights the unexplored production of novel PAN composite fibers with addition of very low percentage of LCGO without using any surface modifications or coating. Following the coagulation process, as spun PAN/LCGO fibers were passed through a series of wash baths operated at various temperatures and multiple hot stretching baths prior to drying, and taken-up using a traversing winder. Current study also investigates the chemical and microstructural changes of PAN due to the addition of very low amounts of GO without the use of binders or surface treatments. The tensile strength and tensile modulus of the fibers were significantly improved with low filler content up to 1 wt% of LCGO into PAN dope that is, a 115% improvement of tensile strength and 152% increase of tensile modulus were achieved at a filler loading of 0.5 wt% whereas 138% improvement in tensile strength at 1 wt% of LCGO. This study revealed that it is possible to produce high strength precursor fibers by wet spinning with the addition of low filler content by make use of LCGO in PAN solution; this can further provide pathways for making high performance carbon fibers.

Clean and low-cost synthesis of high purity beta-silicon carbide with carbon fiber production residual and a sandstone

Abstract The U.S. Department of Energy has initiated conversion of coal to solid materials, which can improve the coal-derived high-value product chain and decrease coal utilization related carbon dioxide emission. An integrated coal utilization technology was developed to respond to Department of Energy's call, which is extracting the molecules with desired molecular weight and structure in coal for carbon fiber production, then using carbon-rich residual from carbon fiber precursor extraction as carbon source to produce beta-silicon carbide. For the first time beta-silicon carbide is synthesized from carbon fiber production residual and a sandstone. The synthesized beta-silicon carbide was characterized with multiple analytical techniques. The product exhibits good properties with its purity, density, and Vickers hardness reach the requirements of commercial silicon carbide. Specifically, the purity of the beta-silicon carbide obtained with the two inexpensive raw materials under argon atmosphere at 1600 °C reaches as high as 98%. It is the first time that the furnace-MS system was applied to analyze the gaseous products in coal-based beta-silicon carbide synthesis process. Also, a possible synthesis mechanism was proposed and confirmed with experimental results. The research further analyzed the environmental impact and proposed the possibility that the liquid wastes/byproducts generated during raw material treatment process can be recycled and efficiently reused as coagulants or desiccants when the developed beta-silicon carbide synthesis process is applied in industry. This study provides a clean and low-cost approach for reusing waste residual from coal-based carbon fiber production and sandstone powder.

Rheology of Polyacrylonitrile/Lignin Blends in Ionic Liquids under Melt Spinning Conditions.

Lignin, while economically and environmentally beneficial, has had limited success in use in reinforcing carbon fibers due to harmful chemicals used in biomass pretreatment along with the limited physical interactions between lignin and polyacrylonitrile (PAN) during the spinning process. The focus of this study is to use lignin obtained from chemical-free oxidative biomass pretreatment (WEx) for blending with PAN at melt spinning conditions to produce carbon fiber precursors. In this study, the dynamic rheology of blending PAN with biorefinery lignin obtained from the WEx process is investigated with the addition of 1-butyl-3-methylimidazolium chloride as a plasticizer to address the current barriers of developing PAN/lignin carbon fiber precursors in the melt-spinning process. Lignin was esterified using butyric anhydride to reduce its hydrophilicity and to enhance its interactions with PAN. The studies indicate that butyration of the lignin (BL) increased non-Newtonian behavior and decreased thermo-reversibility of blends. The slope of the Han plot was found to be around 1.47 for PAN at 150 °C and decreased with increasing lignin concentrations as well as temperature. However, these blends were found to have higher elasticity and solution yield stress (47.6 Pa at 20%wt BL and 190 °C) when compared to pure PAN (5.8 Pa at 190 °C). The results from this study are significant for understanding lignin–PAN interactions during melt spinning for lower-cost carbon fibers.

Fiber formation and properties of polyester/lignin blends

ABSTRACTThermotropic liquid crystalline polyesters with varied chemical structure are synthesized by melt transesterification polycondensation. They are employed as matrix for blends with lignin materials to obtain melt‐spinnable precursors for carbon fibers. The lignin samples are carefully purified by fractionation, enzymatic removal of reducing sugars, and subsequent modification of the terminal OH groups. Effective melt blending is achieved with liquid‐crystalline aromatic–aliphatic polyesters having melting ranges that match the softening temperature of the lignin fractions, which is necessary to prevent thermal decomposition of the lignin. Polyester/lignin blends are partially compatibilized, phase‐separated materials. The polyester/lignin materials are melt‐spun successfully. The fiber properties depend on the lignin purification process. X‐ray scattering reveals that orientation in lignin‐containing fibers is maintained. First experiments show that the fibers can be converted successfully to carbon fibers by thermal annealing procedures. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48257.

Preparation, Stabilization and Carbonization of a Novel Polyacrylonitrile-Based Carbon Fiber Precursor.

The quality of polyacrylonitrile (PAN) precursor has a great influence on the properties of the resultant carbon fibers. In this paper, a novel comonomer containing the sulfonic group, 2-acrtlamido-2-methylpropane acid (AMPS), was introduced to prepare P(AN-co-AMPS) copolymers using itaconic acid (IA) as the control. The nanofibers of PAN, P(AN-co-IA), and P(AN-co-AMPS) were prepared using the electrospinning method. The effect of AMPS comonomer on the carbon nanofibers was studied using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Raman spectrum. The structural evolutions of PAN-based nanofibers were quantitatively tracked by FTIR and XRD during the thermal oxidative stabilization (TOS) process. The results suggested that P(AN-co-AMPS) nanofibers had the lower heat release rate (ΔH/ΔT = 26.9 J g−1 °C−1), the less activation energy of cyclization (Ea1 = 26.6 kcal/mol and Ea2 = 27.5 kcal/mol), and the higher extent of stabilization (Es and SI) during TOS process, which demonstrated that the AMPS comonomer improved the efficiency of the TOS process. The P(AN-co-AMPS) nanofibers had the better thermal stable structures. Moreover, the carbon nanofibers derived from P(AN-co-AMPS) precursor nanofibers had the better graphite-like structures (XG = 46.889). Therefore, the AMPS is a promising candidate comonomer to produce high performance carbon fibers.

Controlled Radical Polymerization of Crude Lignin Bio-oil Containing Multihydroxyl Molecules for Methacrylate Polymers and the Potential Applications

In this work, methacrylate polymers with different thermal and viscoelastic properties were synthesized from red oak lignin bio-oil. The bio-oil, also called pyrolytic lignin (PL), consisted of various phenolic monomers and oligomers with average hydroxyl content of 3.04 mol/mol. The PL was first esterified with different amounts of methacryloyl chloride and acetyl chloride to form PL methacrylates and then subjected to reversible addition–fragmentation chain transfer polymerization. Polymerization of fully methacrylated PL caused gelation to yield a cross-linked polymer. On the other hand, gel-point suppression occurred in the polymerization of partially methacrylated PL to yield a thermoplastic polymer with glass transition temperature (Tg) of 161 °C and thermal decomposition temperature (Td) of 241 °C. In comparison, the functionalization of PL by partial methacrylation and subsequent acetylation resulted in a polymer with Tg of 130 °C and Td of 250 °C. Unlike other biobased methacrylate polymers that cannot withstand high temperatures and volatilize, the polymers produced from this study retained 25–28% mass when pyrolyzed to 1000 °C. The latter polymer was also melt-spinnable and demonstrated highly attractive properties as an ideal carbon fiber precursor. Other than its narrow molecular weight distribution and high isothermal stability, this lignin-based polymer also had a linear molecular orientation that is critical in producing high-quality carbon fiber.

Identifying breach mechanism during air‐gap spinning of lignin–cellulose ionic‐liquid solutions

ABSTRACTTo be able to produce highly oriented and strong fibers from polymer solutions, a high elongational rate during the fiber‐forming process is necessary. In the air‐gap spinning process, a high elongational rate is realized by employing a high draw ratio, the ratio between take‐up and extrusion velocity. Air‐gap spinning of lignin–cellulose ionic‐liquid solutions renders fibers that are promising to use as carbon fiber precursors. To further improve their mechanical properties, the polymer orientation should be maximized. However, achieving high draw ratios is limited by spinning instabilities that occur at high elongational rates. The aim of this experimental study is to understand the link between solution properties and the critical draw ratio during air‐gap spinning. A maximum critical draw ratio with respect to temperature is found. Two mechanisms that limit the critical draw ratio are proposed, cohesive breach and draw resonance, the latter identified from high‐speed videos. The two mechanisms clearly correlate with different temperature regions. The results from this work are not only of value for future work within the studied system but also for the design of air‐gap spinning processes in general. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47800.

Siliciding of carbon fabrics with gaseous SiO

Silicon carbide fabrics were synthesized through siliciding of carbon fiber precursors with gaseous SiO using three original batch-type reactors of different design. The prepared samples were analyzed by XRD and SEM/EDX. It was found that the choice of SiO gas source affected the microstructure characteristics of SiC fiber materials obtained by the proposed method.

Hydrothermal base catalysed treatment of Kraft lignin - time dependent analysis and a techno-economic evaluation for carbon fibre applications

The hydrothermal base-catalysed treatment of industrial Kraft lignin (KL) is investigated as a basis for production of a sustainable carbon fibre precursor, with a focus on the time-dependent evolution and impact on precursor properties. Hydrothermal treatment was performed at T = 300 °C and p = 180 bar, with the retention time (tret) varied between 8, 12, 16, 20, and 24 mins. Molecular weight distribution and thermal stability of the processed lignin were close to maximum after 8 min, and 12–16 min respectively. Chemical modification was found to continue (e.g. demethoxylation) over the entire tret range (24 min). Analysis of the recovered oily phase indicated catechol derivatives were stable end-products with, e.g., vanillin and guaiacol as intermediates. A techno-economic analysis indicated a price of ca. 1600 €/t at a production capacity of 10 kt/a is achievable, with main cost-drivers being lignin (60%), fixed costs (20%), and energy (10%).

Thermal, Mechanical, and Microstructural Study of PBO Fiber during Carbonization.

Poly(p-phenylene benzobisoxazole) (PBO) fiber shows fascinating properties including excellent mechanical performance, high crystallinity, and fairly good heat resistance as a kind of polymer fiber. Its properties make it a possible candidate as a precursor of carbon fiber. This paper mainly investigates the possibility of yielding carbon fiber from PBO by direct carbonization using a continuous process and multiple properties of yielded fiber treated under different heat treatment temperature (HTT). The results show that PBO fiber was able to sustain an HTT as high as 1400 °C under the inert atmosphere and that the shape of fiber was still preserved without failure. Using thermal gravimetric analysis (TGA) and TGA coupled with mass spectroscopy (TGA-MS), it was found that a significant mass loss procedure happened around 723.3 °C, along with the emission of various small molecules. The mechanical performance first suffered a decrease due to the rupture of the PBO structure and then slightly increased because of the generating of graphite crystallite based on the broken structure of PBO. It was observed that PBO’s microstructure transformed gradually to that of carbonaceous material, which could be the reason why the change of mechanical performance happened.

Safer and more effective route for polyethylene-derived carbon fiber fabrication using electron beam irradiation

As a precursor constitutes 50% of total production cost, adopting low-cost precursors for carbon fiber (CF) fabrication has been used as a major strategy to translate exotic carbon fiber technology into a commercial market. Polyethylene (PE), one of the cheapest and the most widely used plastics, has gained lots of tractions as a low-cost CF precursor ensuring stable price and supply. However, the major problem is that the only known CF fabrication protocol using PE includes sulfonation process, which generates toxic SOx fumes. Such toxic fuming does not comply safety and environmental regulations, thereby obstructed bringing PE based CFs into the real world applications. In this study, for the first time, we could demonstrate the fabrication of PE based carbon fiber without SOx fume generation by adopting electron beam pre-treatment. Electron beam technology served various industry fields for decades and it has been well known that active radicals are introduced into polymer chains by electron beam irradiation. Those active radicals are speculated to enable stabilization under significantly mild condition where no toxic fumes were generated. As a result, carbon fiber with sound properties reaching tensile strength of 1.3 GPa could be fabricated through shorter processing time.