Carbon Fiber Precursor Research Articles

Recent Advances in Enhancing Oxygen Reduction Reaction Performance for Non‐Noble‐Metal Electrocatalysts Derived from Electrospinning

Carbonaceous materials originated from electrospinning fibers with hierarchical porosity and good conductivity have attracted intensive attention in the field of electrocatalysis, especially for the oxygen reduction reaction (ORR). Large batches of fibers with uniform sizes can be easily fabricated by electrospinning technology as the precursors of carbon fibers, manifesting the potential to develop a large‐scale, low‐cost, high‐activity ORR catalyst production line for new energy devices such as fuel cells and metal–air batteries. Herein, based on a simple understanding of the ORR mechanism and electrospinning technology, those investigations on synthesizing non‐noble‐metal ORR catalysts through electrospinning in recent years are reviewed. The advantages brought by applying electrospinning technology to the preparation of ORR catalysts are briefly explained. Electrospinning fibers with specific structures for ORR catalysis obtained by innovated spinnerets are displayed. Importantly, the strategies of improving ORR performance for electrospinning fibers through substrate functionalization and active site regulation are discussed in detail. Finally, the prospects and challenges of developing electrospinning technology applied to non‐noble metal ORR electrocatalysis are proposed.

Evolution of polyacrylonitrile precursor fibers and the effect of stretch profile in wet spinning

AbstractWet spinning of polyacrylonitrile‐based polymers is a common technique to manufacture carbon fiber precursors. Understanding the role of stretch profile on structural evolution will support efforts to reduce cost and improve process robustness. Fiber stretch generally occurs in three sequential stages: jet stretch, wet stretch (first draw), and hot draw (second draw). In this study, total fiber stretch was kept constant, but distributed differently across the stretch stages yielding three different fiber variants. Samples were collected and analyzed after each stretch stage in order to correlate process parameters to structural information. For all variants, orientation of the ordered phase increases gradually for each stage of stretch while activation energy for the structural relaxation decreases. Alternatively, crystallite size increases substantially during hot draw, which is shown to have the most pronounced effect on cyclization behavior. Given the process conditions, the variant with the lowest jet stretch and highest hot draw demonstrates the highest tenacity and modulus along with the greatest orientation, crystallite size, and highest peak exotherm temperature.

Innovative procedure for 3D printing of hybrid silicon carbide/carbon fiber nanocomposites

AbstractA novel route to fabricating hybrid ceramic matrix composites has been developed. The fabrication is based on the unique combination of additive manufacturing (AM), a preceramic polymer, and a chopped carbon fiber precursor. After introducing the photoinitiator to the preceramic polymer formulation, a photosensitive resin was introduced. The resulting resin was loaded with distinct weight percentages of stabilized polyacrylonitrile nanofiber—the carbon fiber precursor. These formulations were 3D printed, cured, and converted to ceramic phases using a pyrolysis cycle. The end objective of the pyrolysis cycle is the conversion of the polycarbosilane resin into a silicon carbide matrix and the transformation of the PAN polymer into reinforcing carbon nanofibers within one cycle. The results of this work showed that ceramic matrix composite components can be successfully fabricated using a suitable combination of 3D printing, resin formulation, and processing cycle. The pyrolyzed ceramic hybrid composite was fully dense with nearly linear shrinkage and a shiny, smooth surface. Approximately 60% retained weight after pyrolysis to 1350°C was confirmed by thermogravimetric analysis. In terms of crystallography, the ceramic matrix composite displayed three coexisting phases including silicon carbide, silicon oxycarbide, and turbostratic carbon. The results showed this combination of material and processes has a high potential for fabricating hybrid composites with high‐temperature performance and improved mechanical properties combined with complex geometries.

Manufacturing Pitch and Polyethylene Blends-Based Fibres as Potential Carbon Fibre Precursors.

The advantage of mesophase pitch-based carbon fibres is their high modulus, but pitch-based carbon fibres and precursors are very brittle. This paper reports the development of a unique manufacturing method using a blend of pitch and linear low-density polyethylene (LLDPE) from which it is possible to obtain precursors that are less brittle than neat pitch fibres. This study reports on the structure and properties of pitch and LLDPE blend precursors with LLDPE content ranging from 5 wt% to 20 wt%. Fibre microstructure was determined using scanning electron microscopy (SEM), which showed a two-phase region having distinct pitch fibre and LLDPE regions. Tensile testing of neat pitch fibres showed low strain to failure (brittle), but as the percentage of LLDPE was increased, the strain to failure and tensile strength both increased by a factor of more than 7. DSC characterisation of the melting/crystallization behaviour of LLDPE showed melting occurred around 120 °C to 124 °C, with crystallization between 99 °C and 103 °C. TGA measurements showed that for 5 wt%, 10 wt% LLDPE thermal stability was excellent to 800 °C. Blend pitch/LLDPE carbon fibres showed reduced brittleness combined with excellent thermal stability, and thus are a candidate as a potential precursor for pitch-based carbon fibre manufacturing.

The micro-void structure transformation and properties assessment of polyacrylonitrile fibers irradiated by electron-beam as carbon fiber precursor

PAN fibers were irradiated by electron-beam at room temperature in air. The micro-void structure transformation and properties of irradiated PAN fibers were characterized using gel permeation chromatograph, small angle X-ray scattering, differential scanning calorimetry, thermogravimetric analysis and tensile strength. The cross-linking occurred dominantly, and the stable polymer network formed. The gel fraction got saturated at 200 kGy and did not further increase due to the oxidation degradation. The lateral size of micro-voids and the dose were negatively correlated while the length and misorientation of micro-voids expanded with dose increased (61.73 nm–201.06 nm, 7.79°–11.86°). The intense heat release of cyclization reaction was efficiently relieved by irradiation. Meanwhile, carbon yield at 800 °C also increased from 43% to 55% after irradiation at 200 kGy, which increased by 25% compared with original PAN fibers. This study can prefer irradiation conditions to improve PAN based carbon fiber property.

Effect of compatibilizers on lignin/bio-polyamide blend carbon precursor filament properties and their potential for thermostabilisation and carbonisation

Biobased blends from hydroxypropyl modified lignin (TcC) and a biobased polyamide (PA1010) were produced by continuous sub-pilot scale melt spinning process. A reactive compatibilization was employed with the help of two different compatibilizers (ethylene-acrylic ester-maleic anhydride (MA) and ethylene-methyl acrylate-glycidyl methacrylate (GMA)) to enhance the compatibility between the TcC and PA1010. The enhanced compatibility between the TcC and PA1010 achieved by reaction between hydroxyl groups with maleic anhydride groups in the MA compatibilizer or epoxy groups in the GMA compatibilizer via nucleophilic substitution, was confirmed by chemical (Fourier infrared measurements), physical (glass transition, melting and crystallization behaviour), rheological, morphological and tensile properties of the filaments from compatibilized blends. MA compatibilizer required a higher concentration (2 phr) than GMA (1 phr) to achieve an optimal performance because of the difference in the reactive group's concentration within the each compatibilizer. The MA compatibilizer though was more effective than GMA. The precursor blended filaments were successfully carbonized in a lab scale experiment to yield coherent carbon fibres with tensile stress values of 192 ± 77 and 159 ± 95 MPa; and moduli of 16.2 and 13.9 GPa respectively for uncompatibilised and 2% MA compatibilized blends. That the compatibilized carbon fibre properties are slightly inferior may be attributed to the need to accurately control and optimise applied stress during the thermostabilisation and carbonization stages. Notwithstanding, these differences, the results indicate the potential benefit of using compatibilized TcC/PA1010 blend filaments as carbon fibre precursors.

The Thermal Behavior of Lyocell Fibers Containing Bis(trimethylsilyl)acetylene.

This study focuses on the preparation of carbon fiber precursors from solutions of cellulose in N-methylmorpholine-N-oxide with the addition of bis(trimethylsilyl)acetylene, studying their structural features and evaluating thermal behavior. The introduction of a silicon-containing additive into cellulose leads to an increase in the carbon yield during carbonization of composite precursors. The type of the observed peaks on the differential scanning calorimetry (DSC) curves cardinally changes from endo peaks intrinsic for cellulose fibers to the combination of endo and exo peaks for composite fibers. For the first time, coefficient of thermal expansion (CTE) values were obtained for Lyocell fibers and composite fibers with bis(trimethylsilyl)acetylene (BTMSA). The study of the dependence of linear dimensions of the heat treatment fibers on temperature made it possible to determine the relation between thermal expansion coefficients of carbonized fibers and thermogravimetric curves, as well as to reveal the relationship between fiber shrinkage and BTMSA bis(trimethylsilyl)acetylene content. Carbon fibers from composite precursors are obtained at a processing temperature of 1200 °C. A study of the structure of carbon fibers by X-ray diffraction, Raman spectroscopy, and transmission electron microscopy made it possible to determine the amorphous structure of the fibers obtained.

Design of a ductile carbon nanofiber/ZrB2 nanohybrid film with entanglement structure fabricated by electrostatic spinning

Polyacrylonitrile (PAN), a kind of multi-purpose man-made polymer material, has been widely used in various products, including carbon fiber precursor fiber manufacturing. Organic/inorganic nanocomposites can provide precursor material with unique properties due to optimal structural design. Herein, PAN based carbon nanofiber (CNF) coated zirconium borate (ZrB2) particles fiber film was prepared via electrostatic spinning strategy. Crosslinking network between carbon atoms formed at 280 °C due to long chain PAN molecules, which underwent pyrolysis at 800–1200 °C. Scanning electron microscope analysis showed that ductile CNF/ZrB2 hybrid material with entanglement structure was successfully fabricated. Phase composition of the materials was analyzed by X-ray diffractometer, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy, which confirmed the presence of carbon atoms in the materials. Entanglement structure between CNFs and ZrB2 enhanced tensile performance of nanohybrid film, in which CNF film with 25% ZrB2 content exhibited optimal mechanical properties. The design of nanohybrid structure provides facile and universal approach for exploration of organic/inorganic nanocomposites with controlled structures and excellent mechanical properties.

Lignin addition to polyacrylonitrile copolymer solution and its effect on the properties of carbon fiber precursor

Polyacrylonitrile copolymer (PAN) fiber and PAN/lignin (PL) fiber were wet spun from the PAN copolymer solution and PAN/Lignin blend solution using dimethyl sulphoxide (DMSO) solvent. A blend of 90% by weight (wt %) PAN terpolymer and 10wt% lignin dissolved in DMSO was used in wet spinning of PL fiber. Viscoelastic properties of PAN solution and PAN/lignin solution in DMSO were determined by rheometer. The properties of precursor fiber with and without lignin were evaluated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and mechanical testing. The diffusion of lignin out of coagulated filament was observed during wet spinning of PL solution and was quantitatively estimated by UV–Vis studies. DSC results showed that blending lignin with PAN copolymers can improve the thermal oxidation performance of the precursor fiber and accelerate the thermal stabilization process. A schematic illustration has been deduced for the decrease in tensile strength of PL fiber compared to that of PAN fiber.

Delicacy Management on Kiloton Dry Wet Spinning Bath Liquid

During the dry-jet wet spinning process of polyacrylonitrile carbon fiber precursor, the fluctuation of the coagulation bath liquid level affects the stability of the nozzle directly. The motion trajectory and the motion intensity in all directions of the fluid during the movement of the fiber in the coagulation bath fluid field were studied. A three-dimensional model of the cross flow and jet collision motion trajectory was established, and the impact of fluids with different strengths on the surface of the coagulation bath was analyzed. Solidification of the liquid surface in the fitting strength of the peak effect of the return wave overflow trough coupled superimposed to determine the coagulation bath surface to eliminate interfering fluctuations affecting factors. Based on the above analysis, a smart device for real-time monitoring of the coagulation bath air layer has been developed by using the damping equipment in the coagulation bath, where the impact of various fluid waves on the liquid surface can be eliminated on fixed point or position. According to the understanding of kiloton dry-jet wet spinning precursor fiber production line, in-depth exploration has been made to control the high dynamic coagulation bath level effectively from the perspective of technology and delicacy management.

CoMnO2-Decorated Polyimide-Based Carbon Fiber Electrodes for Wire-Type Asymmetric Supercapacitor Applications

In this work, we report the carbon fiber-based wire-type asymmetric supercapacitors (ASCs). The highly conductive carbon fibers were prepared by the carbonized and graphitized process using the polyimide (PI) as a carbon fiber precursor. To assemble the ASC device, the CoMnO2-coated and Fe2O3-coated carbon fibers were used as the cathode and the anode materials, respectively. Herein, the nanostructured CoMnO2 were directly deposited onto carbon fibers by a chemical oxidation route without high temperature treatment in presence of ammonium persulfate (APS) as an oxidizing agent. FE-SEM analysis confirmed that the CoMnO2-coated carbon fiber electrode exhibited the porous hierarchical interconnected nanosheet structures, depending on the added amount of APS, and Fe2O3-coated carbon fiber electrode showed a uniform distribution of porous Fe2O3 nanorods over the surface of carbon fibers. The electrochemical properties of the CoMnO2-coated carbon fiber with the concentration of 6 mmol APS presented the enhanced electrochemical activity, probably due to its porous morphologies and good conductivity. Further, to reduce the interfacial contact resistance as well as improve the adhesion between transition metal nanostructures and carbon fibers, the carbon fibers were pre-coated with the Ni layer as a seed layer using an electrochemical deposition method. The fabricated ASC device delivered a specific capacitance of 221 F g−1 at 0.7 A g−1 and good rate capability of 34.8% at 4.9 A g−1. Moreover, the wire-type device displayed the superior energy density of 60.2 Wh kg−1 at a power density of 490 W kg−1 and excellent capacitance retention of 95% up to 3000 charge/discharge cycles.

Effect of boric acid on the stabilisation of cellulose-lignin filaments as precursors for carbon fibres

The increasing demand for a low-cost and renewable carbon fibre precursor has driven the focus on bio-based precursors. Cellulose-lignin composite fibres are a new approach toward this direction. The combination of cellulose and lignin into a composite fibre could solve some of the current limitations for pure cellulose and lignin fibres. This study investigated the treatment of the composite fibres with boric acid with focus on carbon yield, stabilisation rate and fibre fusion, which is a typical defect in carbon fibre production. The influence of boric acid on the mechanism of stabilisation was studied. The stabilisation time was reduced by 25% through treatment with the reduction of fibre fusion, while the carbon yield increased significantly in comparison to the untreated fibres.

Effect of plasticizers and polymer blends for processing softwood kraft lignin as carbon fiber precursors

Plasticizers depress the glass transition temperature (Tg) of polymers and produce a flowable material at lower temperatures. The use of plasticizers to depress Tg of lignin is important, since at high processing temperatures lignin crosslinks, making it intractable. The goal of this study was to assess plasticizers and polymer blends for the ability to retard a commercial softwood kraft lignin from crosslinking and also serve as thermal and rheological property modifiers during thermal processing in the attempt to produced moldable and spinnable lignin for lignin and carbon fiber products. The Tg of the lignin and the lignin mixed with various amounts of plasticizers and with different thermo-mechanical mixing were determined using differential scanning calorimetry. The Tg and the change in heat capacity at the glass transition (ΔCp) decreased and increased, respectively, about linearly within this plasticizers range with increased plasticizer weight percentage. Gel permeation chromatography results for extruded lignin as well as extruded lignin-plasticizer blends with glycerol, N-allyurea, citric acid with and without sodium hypophosphite, and oleic acid indicate that the presence of these materials reduced the rate of molecular weight increase at temperatures between 100 and 200 °C. Continuous, homogenous films and fibers could be produced by thermal processing with plasticized lignin samples and plasticized lignin-polymer blends, but not with lignin alone. These fibers could be carbonized, yielding up to about 50% of carbon. The present findings have shown the advantages of plasticizers in thermally processing a commercial softwood kraft lignin.

Disassociated molecular orientation distributions of a composite cellulose–lignin carbon fiber precursor: A study by rotor synchronized NMR spectroscopy and X-ray scattering

Cellulose–lignin composite carbon fibers have shown to be a potential environmentally benign alternative to the traditional polyacrylonitrile precursor. With the associated cost reduction, cellulose–lignin carbon fibers are an attractive light-weight material for, e.g. wind power and automobile manufacturing. The carbon fiber tenacity, tensile modulus and creep resistance is in part determined by the carbon content and the molecular orientation distribution of the precursor. This work disassociates the molecular orientation of different components in cellulose–lignin composite fibers using rotor-synchronized solid-state nuclear magnetic resonance spectroscopy and X-ray scattering. Our results show that lignin is completely disordered, in a mechanically stretched cellulose–lignin composite fiber, while the cellulose is ordered. In contrast, the native spruce wood raw material displays both oriented lignin and cellulose. The current processes for fabricating a cellulose–lignin composite fiber cannot regain the oriented lignin as observed from the native wood.

Influence of Synthesis Method on the Properties of Carbon Fiber Precursors Based on Acrylonitrile and Acrylic Acid Copolymers

Influence of Synthesis Method on the Properties of Carbon Fiber Precursors Based on Acrylonitrile and Acrylic Acid Copolymers

Coproduction of Furfural, Phenolated Lignin and Fermentable Sugars from Bamboo with One-Pot Fractionation Using Phenol-Acidic 1,4-Dioxane

A one-pot fractionation method of Moso bamboo into hemicellulose, lignin, and cellulose streams was used to produce furfural, phenolated lignin, and fermentable sugars in the acidic 1,4-dioxane system. Xylan was depolymerized to furfural at a yield of 93.81% of the theoretical value; however, the prolonged processing time (5 h) led to a high removal ratio of glucan (37.21%) in the absence of phenol. The optimum moderate condition (80 °C for 2 h with 2.5% phenol) was determined through the high fractionation efficiency. Consequently, 77.28% of xylan and 84.83% of lignin were removed and presented in the hydrolysate, while 91.08% of glucan was reserved in the solid portion. The formation of furfural from xylan remained high, with a yield of 92.92%. The extracted lignin was phenolated with an increasing content of phenolic hydroxyl. The fractionated lignin yield was 51.88%, which suggested this could be a low-cost raw material to product the activated carbon fiber precursor. The delignified pulp was subjected to enzymatic hydrolysis and the glucose yield reached up to 99.03% of the theoretical.

Recent Advances in the Application of Functionalized Lignin in Value-Added Polymeric Materials.

The quest for converting lignin into high-value products has been continuously pursued in the past few decades. In its native form, lignin is a group of heterogeneous polymers comprised of phenylpropanoids. The major commercial lignin streams, including Kraft lignin, lignosulfonates, soda lignin and organosolv lignin, are produced from industrial processes including the paper and pulping industry and emerging lignocellulosic biorefineries. Although lignin has been viewed as a low-cost and renewable feedstock to replace petroleum-based materials, its utilization in polymeric materials has been suppressed due to the low reactivity and inherent physicochemical properties of lignin. Hence, various lignin modification strategies have been developed to overcome these problems. Herein, we review recent progress made in the utilization of functionalized lignins in commodity polymers including thermoset resins, blends/composites, grafted functionalized copolymers and carbon fiber precursors. In the synthesis of thermoset resins such as polyurethane, phenol-formaldehyde and epoxy, they are covalently incorporated into the polymer matrix, and the discussion is focused on chemical modifications improving the reactivity of technical lignins. In blends/composites, functionalization of technical lignins is based upon tuning the intermolecular forces between polymer components. In addition, grafted functional polymers have expanded the utilization of lignin-based copolymers to biomedical materials and value-added additives. Different modification approaches have also been applied to facilitate the application of lignin as carbon fiber precursors, heavy metal adsorbents and nanoparticles. These emerging fields will create new opportunities in cost-effectively integrating the lignin valorization into lignocellulosic biorefineries.

Cellulose-lignin composite fibres as precursors for carbon fibres. Part 1 – Manufacturing and properties of precursor fibres

Cellulose-lignin composite fibres were spun from ionic liquid (IL) solutions by dry-jet wet spinning. Birch pre-hydrolysed Kraft (PHK) pulp and organosolv beech (BL) or spruce lignin (SL) were dissolved in the IL 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH]OAc) to prepare spinning dopes. Fibres with lignin concentrations of up to 50 % were spun successfully. The fibres were analysed focusing on important properties for the production of carbon fibres (CF). Due to the higher molar mass of the SL compared to the BL, SL showed higher stability in the spinning process, giving higher lignin content in the final fibres. The CF yield after carbonization increased with increasing lignin content. The higher carbon content of SL compared to BL, resulted in moderately higher CF yield of the SL fibres, compared to fibres with BL. Overall, the produced cellulose-lignin composite fibres show great potential as precursors for CF production.

Close Packing of Cellulose and Chitosan in Regenerated Cellulose Fibers Improves Carbon Yield and Structural Properties of Respective Carbon Fibers.

A low carbon yield is a major limitation for the use of cellulose-based filaments as carbon fiber precursors. The present study aims to investigate the use of an abundant biopolymer chitosan as a natural charring agent particularly on enhancing the carbon yield of the cellulose-derived carbon fiber. The ionic liquid 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH]OAc) was used for direct dissolution of cellulose and chitosan and to spin cellulose–chitosan composite fibers through a dry-jet wet spinning process (Ioncell). The homogenous distribution and tight packing of cellulose and chitosan revealed by X-ray scattering experiments enable a synergistic interaction between the two polymers during the pyrolysis reaction, resulting in a substantial increase of the carbon yield and preservation of mechanical properties of cellulose fiber compared to other cobiopolymers such as lignin and xylan.

Cellulose-lignin composite fibers as precursors for carbon fibers: Part 2 – The impact of precursor properties on carbon fibers

Carbon fibers, despite being responsible lightweight structures that improve sustainability through fuel efficiency and occupational safety, remain largely derived from fossil fuels. Alternative precursors such as cellulose and lignin (bio-derived and low cost) are rapidly gaining attention as replacements for polyacrylonitrile (PAN, an oil-based and costly precursor). This study uses a cellulose-lignin composite fiber, to elucidate the influence of precursor fabrication parameters (draw ratio and lignin content) on the efficiency of stabilization and carbonization, from the perspective of the chemical, morphological and mechanical changes. The degradation of cellulose chains was the primary contributor to the decrease in mechanical properties during stabilization, but is slowed by the incorporation of lignin. The skin-core phenomenon, a typical effect in PAN-based carbon fibers production, was also observed. Finally, the carbonization of incompletely stabilized fibers is shown to produce hollow carbon fibers, which have potential application in batteries or membranes.