Pitch-based Carbon Fibers Research Articles

Manufacturing of Pitch Based Carbon Fibers through Microwave Treatments

Carbon fibers (CFs) are characterized by their excellent mechanical properties including high tensile strength and elastic modulus. In terms of manufacturing of CFs, the conventional thermal treatment processes, including stabilization and carbonization, account for at least 46% of the cost, which drastically restricts the widespread application of CFs. This study investigates the use of mesophase pitch-based CFs from different synthetic approaches based on the conventional thermal post-treatment versus microwave hybrid post-treatment processes. CFs were studied by using SEM, FTIR, TGA, XRD, and mechanical properties characterization. Compared with the CFs prepared from the conventional thermal post-treatment process (CFs-T), those by the microwave thermal hybrid post-treatment process (CFs-M) show similar crystalline degree which is confirmed by XRD analysis. The tensile strength and modulus of the CFs-T are 0.290 and 38.6 GPa, and those of the CFs-M are 0.176 and 18.5 GPa, respectively. Microwave treatment is expected to be a much more energy- and time-efficient way for CFs post-treatment and can serve as a potential alternative to the conventional thermal post-treatment process used in carbon fiber manufacturing. Implications of the findings, including the oxygen diffusion, and crystalline structure are highlighted and discussed.

Electroless copper plating mechanism of mesophase pitch-based carbon fibers by the grafting modification of silane couple agents

Electroless copper plating mechanism of mesophase pitch-based carbon fibers (CFs) by the novel silane couple agents (SCAs) sensitization method was investigated based on the three different functional groups of SCAs (KH550, KH570, KH792). The results showed that relatively stable oligomer films could be formed on the surface of CFs after the sensitization treatment with three kinds of SCAs, which promoted adhesion of CFs with copper plating. Besides, a larger crystalline size, lower resistivity, more uniform and continuous coated copper layers were observed in the copper-plated CFs with KH550 grafting modification (Cu@CF-KH550), in comparison with the copper-coated CFs prepared with KH570 or KH 792 grafting modification (Cu@CF-KH570, Cu@CF-KH792). Moreover, Cu@CF-KH550 had the higher thermal stability than Cu@CF-KH570 and Cu@CF-KH792.

Investigation of mechanical behavior and fracture energy of fiber-reinforced concrete beams and panels

This study quantifies the role of carbon fibers as micro-reinforcement in round panels to prevent and slow the formation of cracks. While carbon fiber-reinforced concrete (CFRC) has drawn considerable attention for use in pavements, the majority of CFRC performance assessment is limited to laboratory-scale samples which do not conform to the predominant failure mechanism, yield-line theory, for concrete pavements. In this study, the effects of carbon fiber content and length on flowability, fiber-matrix bond, and mechanical properties were studied and compared to polypropylene fiber. Analysis of the quadratic polynomial fitted surface plot helped to find the most effective fiber content and length. Composite theory was used to predict the flexural strength, and the result were compared to that of experimental results. The last phase consisted of concrete round panels tested under center-point bending in which the failure mechanism under yield line theory was analyzed. Analysis of Variance (ANOVA) model was finally adopted to compare the calculated modulus of rupture in beams and panels. The results showed beneficial effect of CFRC on pre-crack energy absorption, and their role as crack retarders was justified when the absorbed energy was compared to non-fibrous mixes. The residual flexural strength was also improved in beams and round panels reinforced with carbon fibers. Using the composite theory, the experimental-to-predicted flexural strength ratios in PAN-based carbon fibers were in the range of 1.11–1.34. However, the predicted strengths of mixtures with polypropylene and pitch-based carbon fibers were significantly higher than the experimental values.

Spherical boron nitride/pitch‐based carbon fiber/silicone rubber composites for high thermal conductivity and excellent electromagnetic interference shielding performance

AbstractComposites with high thermal conductivity and excellent electromagnetic interference (EMI) shielding performance are very important for the long‐term stable operation of electronic equipment. In this work, we report a simple and effective method to construct thermally and electrically conductive network pathways by hybridizing pitch‐based carbon fiber (PCF) and spherical boron nitride (s‐BN), in which PCF plays the role in building the framework, and s‐BN acts as a bridge to connect the PCF framework. This can simultaneously enhance the thermal conductivity and EMI shielding efficiency (SE) of silicone rubber (SR) composites. The s‐BN10/PCF20/SR composite could achieve 5.81 W m−1 K−1 of bulk thermal conductivity. The total EMI SE reached 51 dB at the X‐band of 8.2–12.4 GHz. In addition, the s‐BN10/PCF20/SR would have a good heat resistance index (HRI). The tensile strength and elongation at break of the s‐BN10/PCF20/SR were 1.08 MPa and 21.98%, respectively, and its density was only 1.391 g/cm3. In brief, this work provides a simple and effective method to fabricate SR composites with light weight, good thermal stability and suitable mechanical properties to be applied in thermal management and EMI shielding of current electronic equipment.

Enhanced thermal conductivity of epoxy resin by incorporating pitch-based carbon fiber modified by Diels-Alder reaction

The ever-increasing power density and high integration of electronic devices and components greatly promotes the demand for thermal management materials. Herein, we report a lightweight and thermal conductive polymer composite based on the epoxy resin (EP) and high graphitized pitch-based carbon fiber (CF). To address the problem of the surface inertness of the raw CF (RCF), a Dies-Alder reaction was introduced after a conventional oxidation by AgNO3/K2S2O8. The results of the X-ray photoelectron spectroscopy, Raman spectroscopy and scanning electron microscopy showed that the oxygen content of the modified CF (OCF-MA) surface was significantly increased but its structure was not damaged after the Dies-Alder reaction with the maleic anhydride. Because of the superior thermal conductivity and improved surface activity of the RCF-MA, the OCF-MA/EP composites showed a remarkably high thermal conductivity of 4.43 W/m·K at a relatively low CF loading of 11.5 vol%, which is 2.34 times that of the RCF/EP composite (1.89 W/m·K). The infrared thermal imaging method further demonstrated the excellent heat transfer advantage of the RCF-MA/EP composites over the neat EP and RCF/EP composites. The thermogravimetric analysis showed that the addition of OCF-MA has no adverse effect on the thermal stability of the EP composites. In addition, the tensile test showed that the addition of OCF-MA into the EP had a positive effect on the tensile strength of the EP. This work demonstrates that grafting maleic anhydride via Diels-Alder reaction could be a feasible method to functionalize CF for advanced thermal management applications.

Pressure-Strengthened Carbon Fibers from Mesophase Pitch Carbonization Processes.

Little attention has been devoted to studying the pressures during the mesophase pitches carbonization processes and their effects on the as-produced carbon fibers' mechanical properties. Herein, we study the pressure-enhanced graphitization of mesophase pitch and the promoted tensile stresses of the produced carbon fibers using full atomistic simulations based on reactive force fields. Results show that pressures increase the tensile stress of as-produced fibers by 3.7-11 times under 1-6 GPa isotropic compressing pressure. The highest tensile stress can reach 4.39 GPa in carbonized coal tar pitch at 4000 K under 6 GPa. In experimental work, the pressurized laser-processed mesophase pitch generates less gas and shows more ordered carbonized structures in Raman spectra. This work provides a fundamental understanding of the reaction mechanism of carbon fiber production under pressure, and also illustrates a promising method to manufacture mesophase pitch-based carbon fibers with exceptional mechanical properties.

Construction of continuous heat conductive channel, a double harvest strategy to enhance thermal conductance and bending strength of C/SiC composites

The development of efficient and quick method to prepare structure-function integrative C/SiC composites is always a major challenge in this field. Herein, the thermal conductivity and bending strength of C/SiC composites were enhanced simultaneously via continuous high heat conductive channels constructed by continuous wave laser machining and pitch-based high thermal conductivity carbon fiber in thickness direction. Results revealed that the thermal conductivity of the modified C/SiC composites is three times higher than that of referential C/SiC composites due to its highly ordered heat conducive channel in the thickness direction. Importantly, the bending strength of modified C/SiC composites increased to 457 MPa. To better understand the enhance mechanism, the micro-structure for both the composites and heat conductive channel was systematically analyzed. The results demonstrated that the rivet effect of heat conductive channel and the formed two phases structure on the fibers dispersed partial of load and finally enhanced the property of the composites. In a word, this method holds a nice applicable future in constructing structure-function integrative C/SiC composites.

Atoms to fibers: Identifying novel processing methods in the synthesis of pitch-based carbon fibers.

Understanding and optimizing the key mechanisms used in the synthesis of pitch-based carbon fibers (CFs) are challenging, because unlike polyacrylonitrile-based CFs, the feedstock for pitch-based CFs is chemically heterogeneous, resulting in complex fabrication leading to inconsistency in the final properties. In this work, we use molecular dynamics simulations to explore the processing and chemical phase space through a framework of CF models to identify their effects on elastic performance. The results are in excellent agreement with experiments. We find that density, followed by alignment, and functionality of the molecular constituents dictate the CF mechanical properties more strongly than their size and shape. Last, we propose a previously unexplored fabrication route for high-modulus CFs. Unlike graphitization, this results in increased sp3 fraction, achieved via generating high-density CFs. In addition, the high sp3 fraction leads to the fabrication of CFs with isometric compressive and tensile moduli, enabling their potential applications for compressive loading.

Synergistic enhancement in electrical conductivity of polymer composites simultaneously filled with multi-walled carbon nanotube and pitch-based carbon fiber via one-step solvent-free fabrication

Recently, studies have been reported to synergistically improve the electrical conductivity of polymer composites by simultaneously incorporating hybrid fillers, but systematic studies on filler loading and ratio are still scarce. In this study, a one-step process was proposed to induce the incorporation of uniformly dispersed fillers with a high content, and synergistic improvement in the electrical conductivity of polymer composites was studied by applying two types of carbon fillers: nano-sized multi-walled carbon nanotube (MWCNT) and micro-sized pitch-based carbon fiber (PCF). Based on the proposed process, it was possible to fabricate a polymer composite in which the filler was uniformly dispersed within 40 wt%. The electrical conductivity of the composite containing up to 10 wt% MWCNT which was the percolation plateau content and 30 wt% PCF was 3940 S m−1, showing the maximum performance. This result was improved by 595% and 586%, respectively, compared to the electrical conductivity of the composite containing only 40 wt% MWCNT or PCF. These findings can contribute to expanding the application of conductive composites in the fields of antistatic or electromagnetic interference shielding by providing insight into the optimal design of hybrid filler systems to improve the electrical conductivity of composites.

Pitch-Based Carbon Fibers: Manufacturing Status and Modification of Properties

Pitch-Based Carbon Fibers: Manufacturing Status and Modification of Properties

Thermal conductivity and bending strength of SiC composites reinforced by pitch-based carbon fibers

In this work, pitch-based carbon fibers were utilized to reinforce silicon carbide (SiC) composites via reaction melting infiltration (RMI) method by controlling the reaction temperature and resin carbon content. Thermal conductivities and bending strengths of composites obtained under different preparation conditions were characterized by various analytical methods. Results showed the formation of SiC whiskers (SiCw) during RMI process according to vapor—solid (VS) mechanism. SiCw played an important role in toughening the Cpf/SiC composites due to crack bridging, crack deflection, and SiCw pull-out. Increase in reaction temperature during RMI process led to an initial increase in thermal conductivity along in-plane and thickness directions of composites, followed by a decline. At reaction temperature of 1600 °C, thermal conductivities along the in-plane and thickness directions were estimated to be 203.00 and 39.59 W/(m·K), respectively. Under these conditions, bending strength was recorded as 186.15±3.95 MPa. Increase in resin carbon content before RMI process led to the generation of more SiC matrix. Thermal conductivities along in-plane and thickness directions remained stable with desirable values of 175.79 and 38.86 W/(m·K), respectively. By comparison, optimal bending strength improved to 244.62±3.07 MPa. In sum, these findings look promising for future application of pitch-based carbon fibers for reinforcement of SiC ceramic composites.

Preparation and characterization of carbon fiber reinforced plastics (CFRPs) incorporating through-plane-stitched carbon fibers

In this study, novel methods are proposed for manufacturing carbon fiber-reinforced plastics (CFRPs) to enhance their thermal and electrical conductivities and mechanical properties. Polyacrylonitrile (PAN)- and pitch-based carbon fibers were used as the stitching materials, to provide conductive paths through the CFRP body in the through-plane direction. The through-plane thermal and electrical conductivities of the stitched CFRPs were drastically enhanced by a maximum of 2.23 times, and 54.7 times compared to non-stitched CFRP, respectively. The mechanical properties of the stitched CFRPs were also investigated using dynamic mechanical analysis. The results indicate that the pitch-based carbon fibers enhanced the storage modulus of CFRPs, while CFRPs stitched using PAN-based carbon fibers showed decreased value. A thin metal coating was applied to both sides of the CFRPs, and the through-plane thermal conductivity of the silver-coated, stitched CFRPs was slightly enhanced (maximum of 9%), while the through-plane electrical conductivity of the CFRPs was dramatically enhanced (maximum of 498 times). The results indicate that a synergistic effect between the stitched carbon fibers and metal coating can improve the through-plane thermal and electrical conductivities of the CFRPs. This implies that CFRPs manufactured using these simple and effective strategies can be used in the space industry.

Engineering microstructure toward split-free mesophase pitch-based carbon fibers

Engineering microstructure toward split-free mesophase pitch-based carbon fibers

Effect of mechanical properties and surface treatment on fiber breakage AE of CFRP

In this paper, Acoustic emissions by fiber breakage under tensile test of single fiber composites were analyzed using wavelet transformation. PAN-based and two types of pitch-based carbon fibers were used in this study. Surface treatments by acetone or ethanol were conducted. Two AE sensors were used for detecting AE waveforms and the time-frequency diagrams were obtained. Experimental results showed that three damage modes of fiber break (400kHz), interrace fracture (200kHz) and fiber pullout (800kHz) appeared during tests. It appeared that the high frequency component cannot be detected when the sensor located far from the AE source. From the results of frequency analysis, it was found that frequency of fiber breakage was not so affected by Young’s modulus of carbon fibers. It indicated that resonance of resin around a broken fiber governed frequency by fiber break. On the other hand, it was seemed that frequency by fiber break of the acetone-treated fiber was slightly less than the ethanol-treated fiber. It was considered that the interface fracture length affected the frequency.

Improved thermal conductivity and mechanical properties of SiC/SiC composites using pitch-based carbon fibers

Pitch-based carbon fibers were assembled in horizontal and thickness directions of SiC/SiC composites to form three-dimensional heat conduction networks. The effects of heat conduction networks on microstructures, mechanics, and thermal conductivities were investigated. The results revealed the benefit of introducing heat conduction networks in the densification of composites. The maximum bending strength and interlaminar shear strength of the modified composites reached 568.67 MPa and 68.48 MPa, respectively. These values were equivalent to 18.6% and 69.4% increase compared to those of composites without channels. However, channels in thickness direction destroyed the continuity of fibers and matrix, creating numerous defects. As the volume fraction of heat conduction channels rose, the pinning strengthening effect of channels and influence of defects competed with each other to result in first enhanced mechanical properties followed by a decline. The in-plane thermal conductivity was found anisotropic with a maximum value reaching 86.20 W/(m·K) after introducing pitch-based carbon unidirectional tapes. The thermal conductivity in thickness direction increased with volume fraction of pitch-based carbon fibers and reached 19.13 W/(m·K) at 3.87 vol% pitch-based carbon fibers in the thickness direction. This value was 90.75% higher than that of composites without channels.

Effect of reinforcement volume fraction and T6 heat treatment on microstructure, thermal and mechanical properties of mesophase pitch-based carbon fiber reinforced aluminum matrix composites

To meet the requirements of structural and functional integration, machinability and workability of engineering materials, continuous mesophase pitch-based carbon fiber (MPCF) reinforced 2024 aluminum (Al) matrix composites with 20–50 vol % MPCF were fabricated by vacuum hot pressing method. The effects of MPCF volume fraction and T6 heat treatment on microstructure, thermal and mechanical properties of MPCF/2024Al composites were investigated. The results show that the interface of the as-sintered composite was well bonded. After T6 heat treatment, the amorphous layer at the interface changed from continuous to discontinuous and the interfacial bonding was further improved, but there was no interfacial reaction. The increase of MPCF volume fraction was beneficial to improve the thermal conductivity (TC) and elastic modulus (E) of the as-sintered composites, up to 258.3 W/(m⋅K) and 343.5 GPa respectively, while the composites with 30 vol % and 40 vol % MPCF respectively had the highest ultimate tensile strength (UTS) and a coefficient of thermal expansion (CTE) close to zero. After heat treatment, the TC and E were slightly changed, while the CTE was further reduced and UTS was significantly improved. In this work, the heat-treated composite with 30 vol % MPCF had the highest UTS of 499.3 MPa and good thermal properties, and the TC of this composite may be further improved by using MPCFs with higher TC. Therefore, this composite is expected to become a promising engineering material integrating structure and function.

Extrusion Dwell Time and Its Effect on the Mechanical and Thermal Properties of Pitch/LLDPE Blend Fibres

Mesophase pitch-based carbon fibres have excellent resistance to plastic deformation (up to 840 GPa); however, they have very low strain to failure (0.3) and are considered brittle. Hence, the development of pitch fibre precursors able to be plastically deformed without fracture is important. We have previously, successfully developed pitch-based precursor fibres with high ductility (low brittleness) by blending pitch and linear low-density polyethylene. Here, we extend our research to study how the extrusion dwell time (0, 6, 8, and 10 min) affects the physical properties (microstructure) of blend fibres. Scanning electron microscopy of the microstructure showed that by increasing the extrusion dwell from 0 to 10 min the pitch and polyethylene components were more uniformly dispersed. The tensile strength, modulus of elasticity, and strain at failure for the extruded fibres for different dwell times were measured. Increased dwell time resulted in an increase in strain to failure but reduced the ultimate tensile strength. Thermogravimetric analysis was used to investigate if increased dwell time improved the thermal stability of the samples. This study presents a useful guide to help with the selection of mixes of linear low-density polyethylene/pitch blend, with an appropriate extrusion dwell time to help develop a new generation of potential precursors for pitch-based carbon fibres.

Enhancing the electrical insulation of highly thermally conductive carbon fiber powders by SiC ceramic coating for efficient thermal interface materials

Mesophase pitch-based carbon fibers (MPCFs), which have ultrahigh intrinsic thermal conductivity and one-dimensional morphology with high-aspect ratios, can act as excellent fillers for improving the oriented heat dissipation rate of thermal interface materials (TIMs). However, the high electrical conductivity hinders their application in some electronic packaging fields. Herein, a SiC ceramic layer is uniformly and firmly coated on the surface of the powder-like MPCFs by a dynamic chemical vapor deposition method to obtain the high thermal conductivity and suitable electrical insulation. The ceramic coating layer exhibits a porous structure, complete encapsulation and adjustable thickness in the range of 90–600 nm. Employed as the thermal conductive fillers, the SiC-coated MPCF-derived TIMs exhibit comparable thermal conductivity and significantly enhanced electrical insulation performance compared with that from original carbon fiber. For instance, the pad prepared from the coated carbon fiber with a medium coating thickness of 200 nm shows a high through-plane thermal conductivity of 12.8 W m−1 K−1, high electrical resistivity of 3.4 × 1010 Ω cm and satisfactory breakdown voltage value of 1100 V mm−1. This work opens a new avenue to integrate the thermal conductivity and electrical insulation of carbon materials as thermal conductive fillers for electronic packaging.

Carbon fiber reinforced elastomeric thermal interface materials for spacecraft

Due to the high-heat flux issue caused by the increasing power consumption of electronic devices in spacecraft, there is an urgent need but still a significant challenge to develop high thermal conductivity elastomeric thermal interface materials (TIMs) for spacecraft. In this study, mesophase pitch-based carbon fibers (CFs) are added as fillers on the basis of conventional alumina/silicone rubber TIMs, and the CFs are oriented in the matrix by a strong magnetic field during the preparation process. Attributed to the phonon-transport highways composed of vertically-oriented CFs and the synergistic improvement based on CFs and alumina, the through-plane thermal conductivity of the final elastomeric composite with 20 vol% CFs is increased by nearly 14 times compared with the alumina/silicone rubber composite, and it also confirms to the vacuum outgassing performance standard for spacecraft. Moreover, with the help of a verification system, the actual heat transfer capability of the composite is evaluated through the ground test and on-orbit test, and the results suggest that it has a perfect interface heat transfer capability both on the ground and in space, which reveals that this composite can potentially be applied as elastomeric TIM for spacecraft thermal control.

Microstructure of high thermal conductivity mesophase pitch-based carbon fibers

Microstructure of high thermal conductivity mesophase pitch-based carbon fibers