2019 Vol. 34, No. 1

Graphical Contents
2019, 34(1): .
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2019, 34(1): .
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Characterization of the microstructures of carbon fibers by X-ray diffraction
LI Deng-hua, LU Chun-xiang, HAO Jun-jie, YANG Yu, LU Xiao-xuan, DU Su-jun, LIU Zhe
2019, 34(1): 1-8.
Abstract(811) PDF(461)
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Progress on the study of the structural features of carbon fibers using X-ray diffraction is reviewed, including the crystalline structural parameters of carbon fibers, orientation of crystallites along the fiber axis, degree of graphitization and micro-stress/microstrain, as well as their evolution during the manufacture of carbon fibers.
Effect of gelation time on the microstructures, mechanical properties and cyclization reactions of dry-jet gel-spun polyacrylonitrile fibers
LI Xiao-peng, SUO Xi-dong, LIU Yao-dong, LI Yong-hong
2019, 34(1): 9-18. doi: 10.1016/S1872-5805(19)60001-6
Abstract(539) PDF(371)
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The use of gel spinning technology in the formation of polyacrylonitrile (PAN)-based carbon fibers has led to significant tensile property improvements. PAN, dimethylsulfoxide (DMSO) and dimethylformamide (DMF) solutions were dry-jet spun, gelled in methanol at -20 and -50℃ for different times from 0 to 40 d, and vacuum-dried at 0℃ for 24 h to obtain PAN fibers that were drawn to a drawing ratio (DR) of 4 in a hot glycerin bath at 110℃, and then to various DRs in a glycerin bath at 155℃. The effects of gelation time on the microstructures, mechanical properties and cyclization reactions of the gel-spun PAN fibers were investigated. Results showed that the gelation time affected the gel structure and the maximum possible draw ratio. The gelation effects were significant in the first 5-10 d, and were more prominent for the DMSO system than the DMF system. The maximum possible draw ratio, strength and modulus, orientation and crystallinity of the PAN fibers increased with gelation time. The cyclization temperature decreased and the reaction enthalpy increased with gelation time in cyclization, indicating an improved chain orientation and crystallinity with gelation time. Gelation was an important step affecting the microstructures and properties of gel-spun PAN fibers for making high performance carbon fibers.
Effect of crosslinking method on the microstructures and properties of polyimide-based graphite fibers
XIAO Meng, XU Hong-yu, MA Zhao-kun, SONG Huai-he
2019, 34(1): 19-28.
Abstract(417) PDF(244)
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Different polyimide (PI) fibers with and without carboxyl groups on the polymer chain were prepared by dry-jet wet spinning using 1,2,4,5-benzene tetracarboxylic dianhydride (PMDA), p-phenylenediamine (p-PDA) and 3,5-diaminobenzoic acid (DABA) as the PI monomers with a PMDA/(DABA+ p-PDA) mass ratio of 1.02:1 and different DABA/p-PDA mass ratios. The PI fibers were chemically crosslinked with 1,4-butanediol to improve their thermal stability. The PI fibers before and after chemical crosslinking were carbonized at 1400℃ for 1 h and graphitized at 2800℃ for 1 h to prepare graphite fibers. Results indicate that the crosslinking by hydrogen bonding between carboxyl groups significantly increased the thermal stability and increased the carbonization and graphitization yields of the PI fibers. The graphitization degree and thermal conductivity of the graphite fibers from the PI with carboxyl groups are higher than those from the corresponding chemically crosslinked ones. The graphitization degree and thermal conductivity increase with the DABA/p-PDA ratio. The highest degree of graphitization (97.9%) was obtained at a DABA/p-PDA ratio of 5:95 while the highest thermal conductivity (245.6 W/(m·K)) was obtained at a DABA/p-PDA ratio of 10:90.
A comparative study of the ablation properties of carbon fiber-reinforced phenolic resin composites with a matrix modified with graphene oxide and graphitic carbon nitride
MA Yuan-yuan, YANG Yu, LU Chun-xiang, LU Xiao-xuan, WU Shi-jie, YU Zhuang
2019, 34(1): 29-37.
Abstract(550) PDF(306)
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The ablative properties of carbon fiber/phenolic resin (CF/PR) composites were investigated for a graphene oxide (GO)- and a graphitic carbon nitride (g-C3N4)-modified matrix with contents of 0.05, 0.1 and 0.2 wt%, respectively. Both the CF/(g-C3N4-PR) and CF/(GO-PR) composites showed much better ablation resistance than the one without g-C3N4 and GO. The optimum contents of g-C3N4 and GO are both 0.1 wt% giving mass ablation rates for CF/(0.1% g-C3N4-PR) and CF/(0.1% GO-PR) that were respectively 44.42 and 28.96% lower than that of the CF/PR composite. The addition of g-C3N4 and GO increases the char yield and the degree of graphitization of the char near the fibers during ablation, which benefits heat dissipation and thereby increases the ablation resistance.
The evolution of microstructure and thermal conductivity of mesophase pitch-based carbon fibers with heat treatment temperature
FAN Zhen, Cao Min, YANG Wen-bin, ZHU Shi-peng, FENG Zhi-hai
2019, 34(1): 38-43. doi: 10.1016/S1872-5805(19)60002-8
Abstract(402) PDF(285)
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The evolution of microstructure and morphology of mesophase pitch-based carbon fibers (MPCFs) with heat treatment temperature (HTT) was investigated by SEM, TEM, Raman spectroscopy and XRD. The thermal conductivity of the MPCFs was examined by a modified 3ω method. Results indicate that the degree of graphitization and the thermal conductivity of the MPCFs increase with HTT. The thermal conductivity of the MPCFs reaches 518 W/m·K at a HTT of 3000℃. The thermal conductivity of MPCFs varies linearly with HTT in two distinct ranges, 1000-2000 and 2300-3000℃, that respectively correspond to the growth and orientation of graphite crystallites.
The effect of the composition of the solution in the coagulation bath on the microstructures of hollow mesoporous polyacrylonitrile fibers
ZHANG Bing, LU Chun-xiang, LIU Yao-dong, ZHOU Pu-cha, YUAN Shu-xia, YU Zhuang
2019, 34(1): 44-50.
Abstract(310) PDF(233)
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Combining the advantages of hollow and mesoporous structures, hollow mesoporous fibers have great potential in the adsorption of macromolecules. Such fibers were fabricated by a wet-spinning method from a polymer mixture of polyacrylonitrile and alkali lignin. The effect of the composition of the solution in the coagulation bath on the microstructures of the hollow mesoporous fibers produced was investigated by SEM, TGA and nitrogen adsorption. Results indicate that the diameter and pore structure of the fibers were changed by the composition of the solution in the coagulation bath. By increasing the concentration of dimethyl sulfoxide, the average pore size of the fibers decreased from 45.3 to 24.4 nm while the outer diameter and porosity reached minima of 137.5 μm and 88.7%, respectively while the wall thickness reached a maximum of 20.3 μm. The fibers can be processed into hollow mesoporous carbon fibers because of their high carbon yield of 40%.
Improved mechanical and thermal properties of carbon fiber/epoxy composites with a matrix modified by montmorillonite/carbon fillers
WU Xue-ping, ZHAO Jun-shuai, RAO Xu, ZHANG Xian-long, WU Yu-cheng, LU Chun-xiang, YANG Yu, SHAO Ze-fan
2019, 34(1): 51-59.
Abstract(383) PDF(197)
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Montmorillonite and carbon (MMT/C) nanofillers was prepared by a hydrothermal method using montmorillonite as the template, chitosan as the carbon source, and were then dispersed in an epoxy resin (EP) to prepare carbon fiber (CF/(MMT/C-EP)) composites by a hot pressing method. Results indicated that when the mass ratio of chitosan to MMT was 0.5, the thermal conductivity, flexural strength and elastic modulus of the composite reach maxima, corresponding to increases of 78.7, 13.4 and 20.4%, respectively, compared with those without a nanofiller. These improvements are ascribed to an improved dispersion of the nanofiller in EP and stronger interface bonding between the fillers and the EP.
Research on the interfacial adhesion properties of carbon fibers modified by sizing agents to polycarbonate using a single-filament fragmentation test
YAO Ting-ting, WU Gang-ping, LIU Yu-ting, SONG Hong-yan
2019, 34(1): 60-67.
Abstract(266) PDF(205)
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The effects of different sizing agents on the interfacial adhesion between carbon fibers and polycarbonate were investigated using a home-made polycarbonate emulsion, and polyvinyl acetate, polyurethane and polyethylene aqueous emulsions as the sizing agents. The chemical structures of the sizing agents were characterized by FT-IR and TG-MS, the surface characteristics of the modified carbon fibers by SEM, XPS and TGA, and the interfacial shear strength (IFSS) between the coated carbon fibers and the polycarbonate by a single-filament fragmentation test. Results showed that IFSS decreased in the following order:polyurethane (29.19 MPa) > polyvinyl acetate (22.58 MPa) > self-made (20.36 MPa) > polyethylene (14.52 MPa). Hydrogen bonds contribute the most to the interfacial adhesion forces while polar interaction contributes less and dispersion forces the least. The highest IFSS using polyurethane is ascribed to the formation of hydrogen bonds at the interface.
Preparation and characterization of polyimide-modified carbon fiber reinforced polyphenylene sulfide composites
WANG Yong-hua, ZHANG Shou-chun, LIU Pei-pei, JING De-qi, ZHANG Xing-hua
2019, 34(1): 68-74.
Abstract(381) PDF(195)
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Polyimide (PI) sizing of carbon fibers (CFs) was performed by coating them with polyamic acid synthesized from pyromellitic dianhydride and 4,4'-oxydianiline, followed by thermal imidization to improve their interfacial strength with polyphenylene sulfide (PPS) in CF/PPS composites. The surface morphology and chemical structures of the PI-sized CFs were characterized by SEM and XPS, respectively. Results indicated that a continuous and uniform PI sizing layer was formed on the surface of the CFs. The number of carbon atoms bonded to nitrogen and oxygen were increased by 9.72% for the PI-sized CFs compared with the as-received CFs. The interlaminar shear strength, the axial compression strength and axial compression modulus of the PI-sized CF/PPS laminated composite increased by 26.39, 26.02 and 19.64%, respectively compared with the composite without PI sizing.
Effect of surface properties and sizing agents on interfacial properties of carbon fiber reinforced polycarbonate composites
ZHANG Wei-su, YANG Chang-ling, YAO Li-li, LI Zhi-hao, LI Sheng-xia, LU Yong-gen
2019, 34(1): 75-83.
Abstract(526) PDF(202)
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Carbon fiber (CF)/polycarbonate composites were prepared by the same method using five different CFs. Two different PAN-based CFs were supplied by Jiangsu Hengsheng Carbon Fibers Inc. Both had been prepared under the same conditions but one had been anodically oxidized and sized with epoxy. The raw fiber (#1) was subjected to three treatments in our lab:(#2) anodic oxidation, (#3) anodic oxidation followed by sizing with polyurethane, and (#4) anodic oxidation followed by sizing with epoxy. The fiber that had been anodically oxidized and sized with epoxy by the manufacturer is designated #5. The surface functional groups, wettability and interlaminar shear strength (ILSS) of the five CFs composited with polycarbonate were investigated and compared. Results indicate that the smallest number of active groups exists on the #1 CFs, their wettability by polycarbonate is the worst and the ILSS of the composite is the lowest (38.1 MPa). The number of active groups on the #2 CFs is greatly increased, their wettability by polycarbonate is improved and the ILSS is increased to 50.6 MPa much higher that that of the composite with #1 CFs. The number of active groups on the #5 CFs is much higher than on the #2 CFs and their wettability is much better, but the ILSS of their composite is the same as that with the #2 CFs. The ILSS of the composite prepared using the #4 CFs is lower (about 31.7-39.5 MPa) than that with the #3 CFs. The number of the active groups on the #3 CFs and their wettability by polycarbonate are comparable to those of the #5 CFs, but their ILSS (60.4 MPa) greater by 18.9%, which is ascribed to the strong interactions between the polyurethane, the CF surface and the polycarbonate.
Effect of the oxygen content and the functionality of spinnable pitches derived from ethylene tar by distillation on the mechanical properties of carbon fibers
SHI Kui, ZHANG Xia-xiang, WU Wei, YANG Jian-xiao, LIU Hong-bo, LI Xuan-ke
2019, 34(1): 84-94. doi: 10.1016/S1872-5805(19)60003-X
Abstract(336) PDF(217)
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Three basic pitches were prepared by the distillation of ethylene tar at 200, 250, or 300℃ for 3 h. Spinnable pitches were produced from them using air-blowing followed by heat treatment at 330℃ for 4 h and are designated P200AT, P250AT and P300AT, respectively. These three pitches, and stabilized fibers and carbon fibers produced from them were characterized by TG-MS, FT-IR, 13C-NMR, XRD, SEM, solubility tests and elemental analysis. The components and oxidation reactivity of the basic pitches, and its influence on the oxygen functionality and microstructures of the spinnable pitches and mechanical properties of the resulting carbon fibers were investigated. Results showed that with increasing distillation temperature the aliphatic carbon content and n-hexane and toluene solubility of the basic pitches decreased, while their aromaticity and planarity increased, and the oxidation reactivity reached a maximum at 250℃. Of the three spinnable pitches P250AT had the highest softening point, highest carbon yield, oxygen content, and C=O content and the highest toluene insoluble fraction. However, the oxygen uptake of P250AT pitch fibers during stabilization was the lowest among the three. This led to a reduction of gas release during carbonization, and therefore the highest carbon yield, the smallest number of defects, the highest tensile strength and the lowest Young's modulus of all the carbon fibers.
Influence of boron on the graphitization of carbon fibers prepared by boron-modified polyacrylonitrile gel fibers
CHEN Li, LU Chun-xiang, JIANG Jun-qi, LU Yong-gen
2019, 34(1): 95-104.
Abstract(384) PDF(220)
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Carbon fibers prepared from boron-doped polyacrylonitrile gel fibers were graphitized at 1600~2400℃, and the graphitized fibers were characterized by inductively coupled plasma atomic emission spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction and mechanical tests to investigate the influence of boron on their microstructures and properties. The results showed that the boron content in the carbon fibers decreased with increasing heat treatment temperature. Boron occupied substitutional sites in carbon network and moved by diffusion during graphitization. The development of crystallite size was not affected but the orientation of the fibers was significantly improved by the low boron content in the fibers, which made the Young's modulus increase substantially and the loss of tensile strength was reduced. The graphitizing temperature of the boron-doped carbon fibers was lowered by 200℃ in order to prepare samples with the same Young's modulus.
Temperature-variable Raman scattering study on micromechanical properties of the carbon fiber reinforced polyimide composite film
RAN Min, JIA Li-shuang, CHENG Chao-ge, WU Qi-lin
2019, 34(1): 105-109. doi: 10.1016/S1872-5805(19)60004-1
Abstract(321) PDF(209)
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Temperature-variable Raman spectroscopy equipped with mapping function was used to investigate the micro-mechanical properties of a carbon fiber (CF) reinforced polyimide(PI)composite film using carbon nanotubes (3 wt%) dispersed in PI as the stress sensor. The stress distributions on CFs and the interface region during heating from 25 to 300℃ were mapped based on the stress sensitive Raman G' band (around 2679 cm-1) shifts of CNTs. Results indicate that thermal motion of PI chain affect the mechanical properties when the CF/CNT-PI film was heated up to 300℃. Both CFs and interface region were compressively stressed below 200℃. The compressive stress decreased with temperature and was approximately eliminated at around 200℃. Tensile stress developed above 200℃ and increased with temperature, which was distributed mainly on CFs. Furthermore, the stress transfer between CFs and matrix was less than 100% due to the thermal stress hysteresis in the PI matrix.
The thermal and mechanical properties of carbon fiber/flake graphite/cyanate ester composites
SHI Pei-luo, WANG Yue-you, GUO Hong-jun, SUN Hong-jie, ZHAO Yun-feng
2019, 34(1): 110-114. doi: 10.1016/S1872-5805(19)60005-3
Abstract(378) PDF(275)
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Prepregs of carbon fiber reinforced cyanate ester (CE) resin matrix composites (CF/CE and CF/(10 wt% FG-CE)) were prepared with a laminate thickness of 2.0 mm and a fiber volume fraction of 60% with and without 10 wt% flake graphite (FG) as the CE filler. The rheological and thermal properties of the CE and FG/CE matrix as well as the thermal conductivity and mechanical properties of the CF/CE and CF/(10 wt% FG-CE) composites were investigated. Results indicated that the viscosity of the FG/CE matrix increased exponentially with increasing FG content and decreased significantly with deformation beyond 0.1% strain. A rheological percolation threshold was found at a FG content of 2-4 wt% and the percolation network of FG was broken at strains above 0.1%. The thermal conductivity of the matrix increased linearly with the FG content up to 0.46 W/(m·K) of 10wt%-FG/CE from 0.23 W/(m·K) of pure CE. The elastic modulus of the matrix increased from 2.9 GPa for pure CE to 4.3 GPa for 10 wt%-FG/CE. The thermal conductivity of the CF/(10 wt% FG-CE) composite was increased by 127% and compressive strength by 31% compared with the CF/CE composite.