Search

In order to evaluate the effects of sizing agents on the wettability, strength loss, and properties of final filament wound structures during filament winding of carbon fibers, three types of sizing agent based on epoxy, epoxy + polyester, and epoxy + polyurethane were used to treat carbon fibers, the surface properties of carbon fiber samples after treatment were evaluated using SEM, infrared spectroscopy, dynamic contact angle analysis, and interlaminar shear strength (ILSS) test, the strength loss caused by fiber damage during filament winding was quantitatively analyzed, and the strength properties of the filament wound structures were characterized by NOL ring test. The results showed that the sizing agent treatment only slightly improved the surface free energy and ILSS of carbon fibers, but it had obvious influence on the strength loss rate of carbon fiber bundles. Added polyester or polyurethane in epoxy-based sizing may improve its protective effect for carbon fiber, and thus decrease strength loss during winding process, result in better tensile properties of carbon fiber filament wound structures. [ABSTRACT FROM AUTHOR]

Thermosetting composites are a range of high‐performance materials with important applications in multiple fields. However, inaccessible damage such as microcracks ingress from the environment may appear with long term use. Over time, the micro‐damage further expands and leads to material failure. The damage includes the interface damage and the matrix damage. Therefore, the healing technology of composites needs to respond and heal the micro‐damage of the interface and resin in the composites synchronously. In this work, siloxane dynamic bond was introduced into matrix and interface respectively. Specifically, a new type of crosslinker containing polysiloxane was synthesized and used to cure epoxy resin. Polyhedral oligomeric silsesquioxane was modified on the surface of carbon fibers (CFs) by sizing method. The prepared resin showed great mechanical properties and thermal stability, while the mechanical strength and surface activity of the CFs were also improved. Due to siloxane chain exchange reaction, matrix and interface could healing synchronously with good healing efficiency. Furthermore, the composites could retain about 65% of their original mechanical properties after healing multiple times. Composites realized synchronous healing of the resin matrix and the interface and laid foundation for extending the service life and performance of advanced resin‐based composites. [ABSTRACT FROM AUTHOR]

Carbon fiber (CF) reinforced matrix composites have been applied widely, however, the interfacial adhesion of composites is weak due to smooth and chemically inert of CF surface. To solve this problem, A polydopamine/nano‐silica (PDA‐SiO2) interfacial layer on carbon fiber surface was constructed via polydopamine and nano‐ SiO2 (CF‐PDA‐SiO2) by a facile and effective method to reinforce polyamide 6 composites (CFs/PA6). The effects of PDA‐SiO2 interfacial layer on crystallization structure and behavior, thermal properties, and mechanical properties of CFs/PA6 composites were investigated. Furthermore, interfacial reinforcement mechanism of composites has been discussed. This interfacial layer greatly increased the number of active groups of CF surface and its wettability obviously. The tensile strength of CF‐PDA‐SiO2/PA6 composites increased by 28.09%, 19.37%, and 26.22% compared to untreated‐CF/PA6, CF‐PDA/PA6, and CF‐SiO2/PA6 composites, respectively, which might be caused by the increased interfacial adhesion between CF and PA6 matrix. The thermal stability, crystallization temperature, crystallinity, and glass transition temperature (Tg) of CF‐PDA‐SiO2/PA6 composites improved correspondingly, attributing to the heterogeneous nucleation of nano‐SiO2 in the crystalline area and hydrogen bonds with molecular chains of PA6 in the amorphous area. This work provides a novel strategy for the construction of interfaces suitable for advanced CF composites with different structures. [ABSTRACT FROM AUTHOR]

Recently, Carbon fiber reinforced thermoplastic polymer (CFRTP) has been widely used in automotive, aviation, and aerospace. However, the traditional epoxy Carbon fiber (CF) sizing for thermosetting composites was unsuitable for high‐performance CFRTP due to the high‐molding temperatures and incompatibility between them. Herein, a novel semi‐aromatic polyamide‐imide (PAI) backbone structure with multi‐ethoxy pendant groups was designed and synthesized via click‐reaction and solvent‐free polymerization. Waterborne PAI sizing was prepared via self‐emulsifying without surfactants. CF/PEEK (polyether‐ether‐ketone) and CF/PEI (polyether‐imide) composites were manufactured. Results showed that novel PAI had excellent thermal stability and solubility, PAI sizing was stable after 6‐month‐storage. Mechanical performances and hydrothermal aging resistance of composites were improved. Compared with commercial‐sized CF (eCF)/PEI, the flexural strength of sCF/PEI increased by 35.2% to 753.47 MPa, and retention rates of them with aging also increased. Noted, mechanisms of interface enhancement were revealed by quantum chemical calculations, ππ stacking and hydrogen bonding between PAI and PEI, PEEK was found. [ABSTRACT FROM AUTHOR]

The development of new bio‐based epoxy resins and the search for new application areas have become important research directions for bio‐based epoxy resins. Using protocatechuic acid (PA) as a bio‐based raw material, brominated alkenes with different chain length were introduced into PA through substitution reaction, and then oxidized to obtain epoxy resins (PA‐EP) with different epoxy values. After that, it was introduced into epoxy resin (diglycidyl ether bisphenol A [DGEBA]) sizing agent to replace part of DGEBA to prepare new sizing agents. Sizing amount test and sizing CF surface morphology show that the introduction of PA‐EP with high‐epoxy value made it easier be adhered to carbon fiber (CF) surface during sizing process. Interfacial shear strength and interlaminar shear strength of composite made of sizing CF (20 wt% PA‐EP‐3) were 56.86% and 30.29% improvement against the bare CF, which was attributed to the increase in surface energy and epoxy groups after CF sizing. Therefore, PA‐EP with high‐epoxy value was applied as sizing agent for improving interface performance of CF for the first time, and this application was less affected by its low‐output problem compared to its application as a matrix resin in the field of composite manufacturing. [ABSTRACT FROM AUTHOR]

It has always been the goal of researchers to enhance the interfacial properties of carbon fiber composites on the basis of maintaining the mechanical strength of carbon fibers. Herein, the technology of zinc nanosheets (Zn NSs) electrophoresis on the surface of carbon fibers is studied, and a method of electrophoresis within 10 s is provided to realize the construction of Zn NSs on the surface of continuous carbon fibers. It is shown that the strength of carbon fibers can be improved by 13.0% due to the ability of Zn NSs to repair the surface defects of carbon fibers. Moreover, the Zn NS bends when the NSs are thermally treated during the curing process of CF/epoxy resin composite. Using the carbon fiber with thermally bent Zn NSs as the anchor, the interfacial interaction of carbon fiber/epoxy composites is improved from 33.5 MPa of desized carbon fiber to 63.3 MPa of Zn NSs‐modified carbon fibers, namely, improvement of 88.9%. The enhancement is ascribed to the special‐shaped anchorage structure on the surface of carbon fibers that are constructed by the bent Zn NSs. [ABSTRACT FROM AUTHOR]

Poor interfacial properties are always one of the bottleneck problems limiting the development of the PBO fiber/epoxy composites. To solve this, we demonstrated a mussel‐inspired molecular regulation strategy of interphase structure using the layer‐by‐layer construction of rigid (PDA) and flexible (PEI) molecules without fiber structure damage. The precise control on the molecular scale can maximally increase the roughness and polar functional group on the fiber surface, thus enhance the chemical bonding and the mechanical interlocking of the interfacial adhesion. In comparison with the untreated fiber, the IFSS and ILSS value of fiber with (PDA/PEI)n have an increment of 86.85% and 80.08%, respectively. Besides, the overall mechanical performance, such as impact strength and dynamic thermal‐mechanical behavior, was also improved significantly, owing to the improved physical‐mechanical attributes of the interphase. In brief, our study presents a non‐destructive interface regulation of PBO fiber composite to enhance its interfacial adhesion and mechanical performance and optimize its structure/function integrated design. [ABSTRACT FROM AUTHOR]

A series of new types of modified hydrosilanes were synthesized, using hydrosilanes and nitrogen heterocycles (triethoxysilane, 2-aminopyrimidine, 1,2,4-triazin-3-amine, benzylamine and 2-aminobenzothiazole), by Si–N cross-dehydrocoupling catalyzed by Ru3CO12. The results of the synthesis were then demonstrated by 1H nuclear magnetic resonance and GPC testing. Furthermore, modified silicone resins were obtained by a hydrolytic condensation reaction catalyzed by tetramethylammonium hydroxide and characterized by TGA, DSC and FT-IR. Next, excellent thermal stabilities were determined (best initial decomposition temperature was approximately 400 °C, T95% was 595 °C, the mass residue rate at 800 °C was 87.2%). Carbon fiber reinforced silicone matrix composites were manufactured according to the technical process developed using DSC and rotary viscometer test results, and the mechanical property (ILSS) showed great improvement from 34.8 to 45.8 MPa because of the modification of Si–N cross-dehydrocoupling. After pyrolysis up to 1000 °C, the composites still showed a superior ILSS value (19.6 MPa) and the modified silicone resins had a more regular and rounded microstructure and appeared to have ceramic-like particles of Si3N4. This work indicated that the silicone resin (Si–N) modified by cross-dehydrocoupling had greater competitiveness in the field of resin matrix composites. [ABSTRACT FROM AUTHOR]

Multiscale carbon fiber/graphene oxide (CF/GO) reinforcements were developed by chemically grafting GO onto the CF surface using tetraethylenepentamine (TEPA) as a bridging agent for methylphenylsilicone resin composites. Chemical structures and surface morphologies of CFs were systematically characterized. GO was uniformly grafted onto the surface of CFs by the formation of chemical bonding between CFs and GO. TEPA and GO grafting could enhance wettability, surface roughness and free energy significantly. The obtained hierarchical reinforcement (CF‐TEPA‐GO) composites offered 48.49 and 31.53% improvements in the interlaminar shear strength (ILSS) and impact toughness, respectively. Moreover, ILSS of CF‐TEPA‐GO composites after hydrothermal aging treatment was 37.65 MPa with a decrease of just 13.96% compared with that of Untreated CF composites (20.52 MPa) with an obvious decrease of 30.37%. Our design technique, starting from facile chemistry and inexpensive materials, can offer a versatile and effective strategy of preparing hierarchical reinforcements for high‐performance composites applications. POLYM. COMPOS., 39:3509–3518, 2018. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The performance of carbon fiber-reinforced composites largely depends on the properties of the fiber-matrix interface. Here, to improve the interfacial strength properties of carbon fiber/epoxy composites, we doped different concentrations of Fe2O3/graphene nanosheets onto the interfacial region of the carbon fiber composites by nano-coating technology. With the aid of the magnetic field, the arrangement of nanosheets could be controlled in the interface. The nanosheets can be arranged on the carbon fiber surface parallel or perpendicularly with different concentrations. The tensile strength and interfacial shear strength of the modified fiber microcomposites had increased by 22.1 and 44.4% respectively with 1.0 mg/mL Fe2O3/graphene nanosheets. The results indicated that the Fe2O3/graphene nanosheets have an important influence on the carbon fibers and carbon fibers composites. [ABSTRACT FROM AUTHOR]

The surface topographies of carbon fibers treated by sizing agents with different graphene oxide (GO) content were investigated by scanning electron microscopy. The surface elements compositions of carbon fibers were determined by X-ray photoelectron spectrometer. The interfacial properties of composites were studied by interfacial shear strength. The thermo-mechanical properties of two typical specimens (CF-G0 and CF-G1 composites) were investigated by dynamic mechanical thermal analysis. The results showed the introduction of GO sheets on carbon fibers surfaces effectively improved the mechanical properties of carbon fibers/epoxy composites. POLYM. COMPOS., 38:2425-2432, 2017. © 2016 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

To enhance interfacial properties of carbon fibers (CFs)-reinforced methylphenylsilicone resin (MPSR) composites, we introduced an appropriate interface reinforced by trisilanolphenyl-polyhedral oligomeric silsesquioxanes (trisilanolphenyl-POSS) between CFs and MPSR with a liquid phase deposition strategy. Chemical bonds among silanol groups of trisilanolphenyl-POSS, hydroxyl-functionalized CF (CF–OH), and silanol end groups of MPSR in the coating were expected to be formed through condensation reaction during the prepared process. CFs with and without sizing treatment-reinforced MPSR composites were prepared by a compression molding method. X-ray photoelectron spectroscopy revealed that trisilanolphenyl-POSS particles enhanced the contents of fiber surface oxygen-containing groups and silicon-containing functional groups. Scanning electron microscopy and atomic force microscopy images showed that trisilanolphenyl-POSS nanoparticles have been introduced onto the fiber surface obviously and the surface roughness increased sharply. Dynamic contact angle analysis indicated that trisilanolphenyl-POSS-modified sizing agent could improve the fiber wettability and surface energy significantly. Short-beam bending test and impact toughness test results showed that the interlaminar shear strength and impact resistance of the sized CFs composites were enhanced greatly with increasing amplitudes of more than 35 and 27% in comparison with those of untreated CF composites, respectively. Cryo-fractured surface topographies of composites confirmed that interfacial adhesion between CFs and MPSR has been improved after sizing treatment. Meanwhile, the sizing treatment does not decrease single fiber tensile strength. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) has attracted much attention for various applications because of its unique electrical, optical, magnetic and piezoelectric properties. ZnO nanowires (NWs) are often grown onto the carbon fiber (CF) surface to improve the electrical conductivity and flexibility of ZnO, and it is important to understand and further enhance the interaction between ZnO NWs and CFs. Herein, ZnO NWs were grown onto carbon fabrics through a facile hydrothermal method, and the pull-off force to detach an individual ZnO nanowire from CF was measured using a nano-manipulator inside a scanning electron microscope chamber. Also, a novel dopamine-based functionalization method was developed to improve the interfacial adhesion between ZnO NWs and CFs. It was found that introducing polydopamine (PDA) on CF could increase significantly the adhesion strength between CF and ZnO NW and their interfacial shear strength with epoxy as measured by the single fiber microbond test. The hierarchical ZnO NWs on CF fabrics were then utilized to fabricate the laminates. The highest mode I and mode II interlaminar toughness were obtained in those laminates comprising CF/PDA/ZnO NWs owing to the high chemical bonding between ZnO NWs and PDA modified CF surface and strong mechanical interlocking between ZnO NWs and epoxy. [ABSTRACT FROM AUTHOR]

The multi-scale reinforcement and interfacial strengthening on carbon fiber (CF)-reinforced methylphenylsilicone resin (MPSR) composites by adding silica-coated multi-walled carbon nanotubes (SiO2-CNTs) were investigated. SiO2-CNT has been successfully prepared via the hydrolysis of tetraethoxysilane in the presence of acid-oxidized multi-walled carbon nanotubes. Transmission electron microscopy, X-ray diffraction, and Fourier Transform infrared spectroscopy were carried out to examine the functional groups and structures of CNTs. Then, SiO2-CNT was incorporated into MPSR matrix to prepare CF/MPSR-based composites by the compression molding method. The effects of the introduced SiO2-CNT on the interfacial, impact, and heat-resistant properties of CF/MPSR composites were evaluated by short-beam bend method, impact test, and thermal oxygen aging experiments, respectively. Experimental results revealed that the CF/MPSR composites reinforced with 0.5 wt% SiO2-CNT showed a significant increase 34.53% in the interlaminar shear strength (ILSS) and 20.10% in impact properties. Moreover, the heat-resistant properties of composites were enhanced significantly by adding SiO2-CNT hybrid nanoparticles. These enhancements are mainly attributed to the improved matrix performance resulted from the molecular-level dispersion of SiO2-CNT in MPSR matrix and the strong interfacial adhesion between SiO2-CNT and matrix resin, which are beneficial to improve the mechanical stress transfer from MPSR matrix to CFs reinforcement and alleviate stress concentrations. [ABSTRACT FROM AUTHOR]

A liquid sizing agent containing multiwall carbon nanotubes (MWCNTs) was prepared for carbon fiber (CF) reinforced methylphenylsilicone resin (MPSR) composite applications. In order to improve the dispersion of MWCNTs in the sizing agent and interfacial adhesion between CF and MPSR, MWCNTs and CF were functioned by the chemical modification with tetraethylenepentamine (TEPA) used as a MPSR curing agents. The CF before and after the sizing treatment-reinforced MPSR composites were prepared by a compression molding method. The microstructures, interfacial properties, and impact toughness of CF were systematically investigated. Experimental results revealed that a thin layer of MPSR coating containing functionalized MWCNTs (MWCNT-TEPA) was uniformly grafted onto the surface of CF. The sized CF-reinforced MPSR composite showed simultaneously remarkable enhancement in the interlaminar shear strength and impact toughness. Meanwhile, the tensile strength of CF had no obvious decrease after sizing treatment. In addition, the interfacial reinforcing and toughening mechanisms were also discussed. We believe that the facile and effective method in preparing multifunctional fibers provides a novel interface design strategy of carbon fiber composites for different applications. [ABSTRACT FROM PUBLISHER]

The thermal degradation kinetics of a home-made epoxy emulsion sizing agent for carbon fiber has been investigated by thermogravimetric analysis (TG). The thermal degradation activation energy, calculated by Flynn–Wall–Ozawa method and Friedman method, is in good agreement with each other, and the values are 214.03 and 220.87 kJ/mol, respectively. The reaction order n (4.7414) and frequency factor A (1.6906 × 1017) were determined by Friedman method. The studies by scanning electron microscope, X-ray photoelectron spectroscopy (XPS), tensile strength of single fiber and interlaminar shear strength (ILSS) revealed that the sizing agent had improved the content of oxygen-containing groups on carbon fiber, increased the tensile strength of single fiber, and effectively enhanced the interfacial properties of carbon fiber/epoxy composites. [ABSTRACT FROM AUTHOR]

The performance of carbon fibers-reinforced composites is dependent to a great extent on the properties of fiber–matrix interface. To improve the interfacial properties in carbon fibers/epoxy composites, nano-SiO2particles were introduced to the surface of carbon fibers by sizing treatment. Atomic force microscope (AFM) results showed that nano-SiO2particles had been introduced on the surface of carbon fibers and increase the surface roughness of carbon fibers. X-ray photoelectron spectroscopy (XPS) showed that nano-SiO2particles increased the content of oxygen-containing groups on carbon fibers surface. Single fiber pull-out test (IFSS) and short-beam bending test (ILSS) results showed that the IFSS and ILSS of carbon fibers/epoxy composites could obtain 30.8 and 10.6% improvement compared with the composites without nano-SiO2, respectively, when the nano-SiO2content was 1 wt % in sizing agents. Impact test of carbon fibers/epoxy composites treated by nano-SiO2containing sizing showed higher absorption energy than that of carbon fibers/epoxy composites treated by sizing agent without nano-SiO2. Scanning electron microscopy (SEM) of impact fracture surface showed that the interfacial adhesion between fibers and matrix was improved after nano-SiO2-modified sizing treatment. Dynamic mechanical thermal analysis (DMTA) showed that the introduction of nano-SiO2to carbon fibers surface effectively improved the storage modulus of carbon fibers/epoxy. [ABSTRACT FROM AUTHOR]

In order to study the interracial reaction of carbon fiber surface coating in the process of preparing composite materials, an experimental method based on dynamics was adopted. Different DSC curve will be obtained from the reaction enthalpy measurement of resin and curing agent, resin and sizing agent, sizing agent and curing agent and so on with different heating rate. The pre-exponential factor A, reaction order n and apparent activation energy E and dynamics equations were calculated by the Kissinger, Flynn-Wall-Ozawa and Crane methods. The activation energy of the sizing agent and curing agent is 47.25 kJ/mol, while the activation energy of the resin and curing agent system is 49.64 kJ/mol. It can be concluded that the carbon fiber surface coating reacts with curing agent first than the resin. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with the effect of emulsifier content of sizing agent on the carbon fibre surface and interface properties of carbon fibre composites. The topographies of carbon fibres surface has been studied by the atomic force microscopy (AFM) and the failure surface of the composites has been studied by scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) has been used to characterize the surface composition of the fibres. The effects of emulsifier content of sizing agent on the adhesion of surface on the interlaminar shear strength were examined. The results indicated that the emulsifier content of sizing agent has an important influence on the carbon fibres and carbon fibres composites. The 20wt% emulsifier content sizing agent (E-3) sized carbon fibres/epoxy resin composite showed better interfacial shear strengths. [Copyright &y& Elsevier]

Abstract: A carbon fiber/polyhedral oligomeric silsesquioxane/carbon nanotube (CF–POSS–CNT) hybrid reinforcement was prepared by grafting CNTs onto the carbon fiber surface using octaglycidyldimethylsilyl POSS as the linkage in an attempt to improve the interfacial properties between carbon fibers and an epoxy matrix. X-ray photoelectron spectroscopy, scanning electron microscopy, dynamic contact angle analysis and single fiber tensile testing were performed to characterize the hybrid reinforcements. Interlaminar shear strength (ILSS), impact toughness, dynamic mechanical analysis and force modulation atomic force microscopy were carried out to investigate the interfacial properties of the composites. Experimental results show that POSS and CNTs are grafted uniformly on the fiber surface and significantly increase the fiber surface roughness. The polar functional groups and surface energy of carbon fibers are obviously increased after the modification. Single fiber tensile testing results demonstrate that the functionalization does not lead to any discernable decrease in the fiber tensile strength. Mechanical property test results indicate the ILSS and impact toughness are enhanced. The storage modulus and service temperature increase by 11GPa and 17°C, respectively. POSS and CNTs effectively enhance the interfacial adhesion of the composites by improving resin wettability, increasing chemical bonding and mechanical interlocking. [Copyright &y& Elsevier]

This study proposes a method of improving the ability of atomic oxygen (AO) erosion resistance for the interface of carbon fiber/epoxy (CF/EP) composites by means of plating gold (Au) on CF surface. Tests of scanning electron microscopy (SEM) and atomic force microscopy (AFM) indicate that Au coating, with the thickness of about 50nm is dense, uniform and complete, and has good adhesion to the CF substrate. Interfacial shear strength (IFSS) of single-fiber microcomposites made from CF and EP before and after AO exposure is measured by single-fiber pull-out instrument. The results show that the IFSS of the single-fiber microcomposites, which are protected by Au coating is hardly affected by AO for long time exposure of 8 h, in contrast to those which are not protected with Au coating, whose IFSS decreased dramatically for an AO exposure time of 2 h. [ABSTRACT FROM AUTHOR]

Abstract: To investigate the effect of γ-ray radiation on the microstructural and mechanical properties of carbon fibers, carbon fibers were irradiated by 60Co source. The interlayer spacing d 002 of carbon fibers decreased after irradiation. The Young’s modulus and density of the fibers increased with increasing dose. The tensile strength of fibers was found to increase at low dose and decrease at high dose. Additionally, Compton scattering effect caused by γ-ray is proposed to be responsible for the structural and mechanical changes of fibers. The results indicated that γ-ray irradiation was an effective method for improving the mechanical properties and graphitization degree of polyacrylonitrile based carbon fibers. [Copyright &y& Elsevier]

Abstract: The changes in oxygen and nitrogen during manufacture of the carbon fiber reinforced resin matrix composites were measured using the X-ray photoelectron spectroscopy method. The effects of the change in oxygen and nitrogen on the strength of the carbon fibers were investigated and the results revealed that the change of the tensile strength with increasing heat curing temperature was attributed to the change in the surface flaws of the carbon fibers because the carbon fibers are sensitive to the surface flaws. The effect of the surface energy that was calculated using Kaelble’s method on the strength of the carbon fibers was investigated. Furthermore, the surface roughness of the carbon fibers was measured using atom force microscopy. The change trend of roughness was reverse to that of the strength, which was because of the brittle fracture of the carbon fibers. [Copyright &y& Elsevier]

Abstract: The carbon fiber/Si–O–C glass composite was prepared from the silicone and carbon fiber by pre-oxidation and spark plasma sintering (sintered composite). The mass loss of the sintered composite oxidized at 1200°C for 90min was 5%, which was lower than that of same dimension for similar composites, although the mass loss at 600°C was still high. This indicated its excellent oxidation resistance at elevated temperature. No cracks and pores were found in the sintered composite, indicating that the combination of pre-oxidation and spark plasma sintering was better than the pyrolysis for manufacturing dense composites. Compared with the flexural strength of about 60MPa for carbonaceous composites, the flexural strength of the sintered composite was obviously improved to 220MPa. Moreover, microstructures of the specimen before and after sintering as well as after oxidation were investigated. [Copyright &y& Elsevier]

The article presents a study which evaluates the interfacial shear strength of carbon fiber (CF) and epoxy microcomposites by the microbond technique and investigates the composition of CF surface by X-ray photoelectron spectroscopy (XPS). The study analyzes the chemisorptions and alignment of adsorbed thiols. Results show that among molecular orientation and chain lengths, the chemical nature of active group was essential for the development of interfacial properties in epoxy or CF composites.

Abstract: A special technique using γ-ray irradiation-induced graft-polymerization was applied to carbon fibers. Epoxy resin and chloroepoxy propane reacted with carbon fibers by a co-irradiation grafting method and acrylic acid was graft-polymerized onto the fiber surface via a pre-irradiation grafting method. The roughness, amount of containing-oxygen functional groups and surface energy were all found to increase significantly after irradiation grafting. Gamma-ray irradiation grafting improved marginally the tensile strength of carbon fibers, which was evaluated by statistical analysis using the Weibull distribution. The interlaminar shear strength of treated carbon fiber/epoxy was enhanced by at least 17.5%, compared with that of untreated carbon fiber/epoxy. The mechanisms of irradiation grafting are proposed by radical reactions. The γ-ray co-irradiation grafting and pre-irradiation grafting are both an effective method for modifying the physicochemical properties of carbon fibers and improving the interfacial adhesion of composites. [Copyright &y& Elsevier]

Abstract: A comprehensive experimental study was conducted to identify the differences of the kidney section carbon fibers and circular section carbon fibers in the surface characteristics of fibers and mechanical properties of composites. It was revealed that the kidney fibers with larger specific surface area have a better adsorption characteristic and higher impregnating performance compared with the circular fibers. Mechanical tests under interfacial shear, interlaminar shear, flexural and compressive load have shown that the kidney fiber/epoxy composites outperform the circular fiber/epoxy composites by a significant improvement of 23.5, 12.7, 7.5 and 4%, respectively. The tensile strength is nearly the same for the two composite systems, but the failure of kidney fiber/epoxy tensile specimens undergoes a cumulative damage progression process and is different from that of circular fiber/epoxy tensile specimens. Also, the kidney fibers have a more non-uniform distribution in composites and larger contact areas with each other compared with the circular fibers, and the mechanical properties of kidney composites have a larger coefficient of variation than those of circular composites. [Copyright &y& Elsevier]

Abstract: Interfacial properties of carbon fibre (CF) reinforced non-polar structure polyarylacetylene (PAA) resin composites were modified through cold oxygen plasma treatment of CF. The effects of plasma treatment on CF were characterized by X-ray photoelectron spectroscopy, atomic force microscope (AFM), and interlaminar shear strength (ILSS). XPS showed that plasma treatment increased the amount of elemental oxygen on fibre surface markedly by introducing more kinds of oxygen groups. AFM images indicated that weak surface regions of fibres had been etched and removed, and the roughness of fibre surface was increased. Furthermore ILSS of CF/PAA composites was improved notably. The influences of treatment time on the plasma oxidation results were studied and optimal treatment time was determined according to the change of ILSS. The conclusion that plasma treatment is an effective method to improve the interfacial properties of carbon fibre reinforced non-polar structural PAA matrix composites, just as doing in polar resin matrix composites, can be drown. [Copyright &y& Elsevier]

Abstract: In this work, the effect of soaking and irradiating in praseodymium nitrate solution on the surface physicochemical properties of carbon fibers and interfacial properties of composites has been investigated, and the interfacial adhesion mechanism of treated carbon fiber/epoxy composite was analyzed. It was found that both of immersion and irradiation lead to an increase of fiber surface roughness, improvement of oxygen-containing groups, enhancement of disorder degree and introduction of praseodymium element on carbon fiber surface. As a result, the coordination linkage between fibers, praseodymium ion and matrix is formed and the interlaminar shear strength (ILSS) of composites is increased, due to the improvement of interfacial adhesion between fibers and matrix resin. Moreover, γ-ray irradiation treatment is superior to immersion treatment in promoting interfacial properties owing to the increase of carboxyl and carbonyl. [Copyright &y& Elsevier]

Abstract: The surface characteristics of carbon fibers were studied by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and wetting measurements. The surface of carbon fiber was modified by means of plasma graft silsesquioxane. The oxygen/carbon and silicon/carbon ratio increased rapidly after treatments. Fitting the C 1s, O 1s, and Si 2p spectra demonstrated that new photopeaks were emerged, which were indicated C–Si, Si–O groups, respectively. The degree of surface roughness and the wettability of carbon fiber surface were both increased by plasma graft silsesquioxane. The results may shed some light on the design of the appropriate surface structure, which could react with resin, and the manufacture of the carbon fiber reinforced composites. [Copyright &y& Elsevier]

Abstract: In this paper, a new treatment method based on molecular self-assembly on carbon fiber surface was proposed for obtaining a controlled interface between carbon fiber and epoxy matrix in composite system. To form the controlled interfacial region, the surfaces of carbon fibers were first metallized by electroless Ag plating, then were reacted with a series of thiols (different chain lengths and terminally functional groups) to form self-assembly monolayers (SAMs), which further reacted with epoxy resin to generate a strong adhesion interface. The morphology, structure and composition of untreated and treated carbon fiber surface were investigated by atomic force microscope (AFM), surface-enhanced Raman scattering spectroscopy (SERS) and X-ray photoelectron spectroscopy (XPS), respectively. SERS study showed that thiols chemisorbed on Ag/carbon fiber in the form of thiolate species via the strong S–Ag coordinative bond. XPS study further confirmed the chemisorption by an S 2p3/2 component observed at 162.2eV. The binding energy was characteristic of silver thiolate. The interfacial shear strength of the carbon fiber/epoxy microcomposites was evaluated by the microbond technique. The results showed that there was a direct effect of the interfacial parameters changes such as chain lengths and surface functional groups on the fiber/matrix adhesion. [Copyright &y& Elsevier]

Abstract: An intermittent electrochemical treatment method was developed in this work which was used to modify the surface of carbon fibers in three-dimensional fabrics. The effects of this treatment on the surface chemical components of the fibers in both interior and surface regions of the fabrics were analyzed by X-ray photoelectron spectroscopy. The wettability of the fabrics was evaluated by liquid-drop method. A microdebonding method was employed to determine the uniformity of interfacial shear strength between the fibers and the matrix in different regions of the carbon fabric/phenolic composites. The compressive strength was also tested to evaluate the effects of treatment. The results indicated that the intermittent electrochemical treatment significantly improved the interfacial adhesion by etching and generating oxygenic and nitrogenous functional groups. The processibility of the fabrics was also improved due to improved impregnation of phenolic resin with the fabrics. The compressive strength was significantly increased due to optimized intermittent electrochemical treatment. Moreover, comparing with the traditional continuous electrochemical treatment which the treatment degrees of the fibers in different region of the fabrics were different, the intermittent treatment was a useful method to obtain the relatively uniform properties throughout the fabrics. [Copyright &y& Elsevier]

Highlights Zeolitic imidazolate framework‐8 (ZIF‐8) was used to enhance the interfacial strength of composites due to its large specific surface area, uniform pore size, and high stability. Morphology‐controllable ZIF‐8 nanocrystals were synthesized by solvent method and a layer of small‐sized and height crystalline ZIF‐8 was deposited on carbon fibers via an efficient electrophoretic deposition (EPD) way. The results showed that interlaminar shear strength (ILSS) and tensile strength (TS) of carbon fibers/epoxy composites and the TS of carbon fiber were enhanced by 43.56% and 25.48%, respectively. The strong interfacial adhesion strength between carbon fibers and epoxy was attributed to improving the wettability, ionic interaction and the mechanical interlocking effect induced by porous ZIF‐8, which led to effective energy absorption and load transfer. This highly efficient and controllable method is believed to improve the mechanical properties of carbon fiber composites for a wide range of industrial uses. ZIF‐8s in different sizes and morphology were synthesized by solvent method. MOF was deposited firstly onto carbon fibers though electrophoretic deposition. Materials Studio was used to evaluate the strong anchoring strength. ILSS of composites was enhanced by 43.56%. [ABSTRACT FROM AUTHOR]

Abstract: High density carbon fiber fabric was modified by using γ-ray irradiation grafting technology in ammonia and gaseous triethylenetetramine. Atomic force microscopy and X-ray photoelectron spectroscopy were performed to characterize the modified carbon fibers. The results showed that the irradiation grafting was much more uniform throughout the thickness of the fabric compared with the traditional commercial electrochemical treatment and the nitrogen-containing functional groups were significantly increased. The single fiber pull-out tests indicated that the interfacial strength of the resulting composites had dramatic increases and the single fiber tensile strength measurements showed that the fiber strength did not have any discernable decrease. [Copyright &y& Elsevier]

Abstract: Carbon fibers were grafted with a layer of uniform octaglycidyldimethylsilyl POSS in an attempt to improve the interfacial properties between carbon fibers and epoxy matrix. Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and dynamic contact angle analysis were performed to characterize the carbon fibers. AFM results show that the grafting of POSS significantly increased the carbon fiber surface roughness. XPS indicates that oxygen-containing functional groups obviously increased after modification. Dynamic contact angle analysis shows that the surface energy of modified carbon fibers is much higher than that of the untreated ones. Results of the mechanical property tests show that interlaminar shear strength (ILSS) increased from 68.8 to 90.5MPa and impact toughness simultaneously increased from 2.62 to 3.59J. [ABSTRACT FROM AUTHOR]

The interfacial self-healing of fiber/matrix materials is an efficient strategy for extend the service life of composites. Here, we constructed the interfacial self-healing carbon fiber/epoxy composites system based on Diels-Alder reaction. Metal-organic frameworks (MOF) after postsynthetic modification (PSM), i.e., UiO-66-maleimide (UiO-66-M) is not only in-situ grafted on carbon fiber (CF) surface, but also used as nanofillers to disperse epoxy resin to fabricate UiO-66-M/epoxy nanocomposites. After growth MOF, the surface energy of CF enhanced from 38.34 to 58.90 mN m−1, the IFSS and ILSS increased by 39.43% and 16.62%, respectively. UiO-66-M rigid structure plays a key role for strengthening the mechanical interlocking. The interface between UiO-66-M-CF and UiO-66-M-EP can be healed three times and the best self-healing efficiency was 90.60%. In addition, UiO-66-M-EP resin can be reprocessed due to the Diels-Alder bonds. [Display omitted] [ABSTRACT FROM AUTHOR]

Considering the development of CFRPs, addressing the challenge through the simplistic industrial operational methods to achieve high strength and toughness in carbon fiber-reinforced epoxy resin (EP) composites (CFRPs) is imperative. In this work, an innovative approach introduced to improve the strength and toughness of CFRPs by application of a nano emulsion encapsulated polyhedral oligomeric silsesquioxane (POSS) sizing agent (POE sizing agent). The employment of a POE sizing agent markedly enhanced the surface energy and roughness of carbon fibers (CF) as well as the interface properties of CFRPs. Furthermore, the 10-PCF (10 wt% POE sizing CF) reinforced EP unidirectional CFRPs demonstrated superior strength and toughness. Relative to the DCF (Desizing CF) reinforced EP unidirectional CFRPs, their interlaminar shear strength, flexural strength, and unnotched impact strength increased by 24.9 %, 37.8 %, and 45.6 %, respectively, reaching 99.8 ± 2.3 MPa, 1376.8 ± 21.6 MPa, and 94.9 ± 4.6 kJ/m2. Concurrently, the 10-PCF reinforced EP composite laminates exhibited outstanding impact resistance, minimal damage area, and enhanced compressive strength after impact. Additionally, the strength, bundling, and flexibility of the sized CF were maintained, ensuring the processability of CF. The utilization of POE sizing agent for strength and toughness improvement in CFRPs offers a straightforward and industrially feasible approach. This research opens up a novel strategy for high-performance CF and CFRPs preparation. [Display omitted] • POE sizing agent has small particle size, high stability, good heat resistance, and environmental friendliness • POSS was encapsulated in nano microspheres so that they could be evenly coated on the CF surface without sedimentation. • POE sizing agent increased the surface roughness of CF, surface energy, and interfacial bonding performance. • POE sizing agent improved the strength and toughness of unidirectional CRRPs. • POE sizing agent improved the CAI of CFRPs from the perspective of interface modification. [ABSTRACT FROM AUTHOR]

Abstract: Four kinds of polyacrylonitrile-based carbon fibers were cleaned by three methods and were characterized by X-ray photoelectron spectroscopy, monofilament tensile strength test and atomic force microscopy (AFM). Experimental results of these tests reveal that the method using supercritical acetone or subcritical potassium hydroxide aqueous solution act as the processing medium shows a better cleaning effect compared to the traditional method, Soxhlet extraction with acetone. The method using supercritical acetone is more appropriate to wipe off the oxygenated contaminants on carbon fibers’ surfaces and causes a relatively smaller damage to the bulk strength of each carbon fiber. As far as treating method using the subcritical alkali aqueous solution, it can thoroughly remove silicious contaminants on the surfaces of treated fibers. [Copyright &y& Elsevier]

Abstract: The oxidation–reduction and pre-irradiation induced methods were employed to study the effect of acrylic acid modification on the wetting and adsorption ability of carbon fiber (CF) in epoxy solution and the interfacial properties of CF/epoxy. Systematic experimental work was conducted to determine the surface topography, surface energy, surface chemical composition, absorbability and tensile strength of carbon fibers and interfacial adhesion of CF/epoxy before and after modification. The roughness, surface energy, amount of containing-oxygen functional groups and wetting ability were all found to increase significantly after modifications. The tensile strength of carbon fibers was improved marginally by γ-ray pre-irradiation while was decreased little by oxidation–reduction modification. Consequently, the surface modifications of carbon fibers via both oxidation–reduction and pre-irradiation led to an improvement (more than 15%) of the interlaminar shear strength of CF/epoxy composites. The mechanisms of interfacial improvement of modified CF/epoxy composites are proposed. [Copyright &y& Elsevier]

Abstract: A new method for characterizing the interfacial performance between fiber and matrix was introduced in this paper, which was called three-parameters exponential pattern method (TPEPM). TPEPM belongs to neither macro- nor micro-measurement method. It was able to characteristic both macro- and micro-interfacial performance of composites efficiently at the same time. It could be attributed to meso mearsurement method. After verified by traditional method (short beam shear), it proved that the method of three-parameters exponential pattern has high reliability. The periodic time of experiment was shorter and could obtain more effective datum than before. The process of producing specimens as well as the procedure of testing was described detailedly. The way of testing the shear strength was according to the following formula:. In this formula, τ is the shear strength (MPa), P the shear force (N), bl express the area of adhesion. The dispersion pattern graph of shear strength (τ) and adhesion area (s) was made. It can be found that they have the similar variation regularity with exponential curve, which was proved by a great deal of experiment. The three-parameters exponential curve was fitted by the method of least squares. The variable regularity of the parameters τ0, τ1 and λ were compared with interlaminar shear strength (short beam shear). It was proved that the method was reliable. [Copyright &y& Elsevier]

PAN-based carbon fibers (PAN-CFs) have been widely used as structural reinforcements of various advanced composites due to their excellent mechanical properties. However, PAN-CFs have no obvious superiority in terms of the heat dissipation ability compared to mesophase pitch-based CFs and vapor grown CFs. In the present work, Poly- p -phenylene benzobisoxazole (PBO) macromolecules, which could contribute to the development of highly ordered graphite from conjugated aromatic backbone, were introduced onto PAN-CF surfaces to prepare coaxial PAN/PBO carbon fibers (PAN/PBO-CFs). Results showed that functional graphene oxide (GO) could result in uniform grafting of PBO macromolecules onto fiber surfaces owing to π–π conjugations between GO and benzoxazole backbone. The coaxial PAN/PBO-CFs were subsequently obtained through high-temperature graphitization and the rigid state could be also retained. Results by XRD and TEM demonstrated that PAN/PBO-CFs had smaller interlayer spacing and higher crystallinity compared to PAN-CF, and PBO derived graphite crystals could also be perpendicular to fiber surfaces. As for the thermal conductivity of composites, the in-plane thermal conductivity of PAN/PBO-CF reinforced epoxy composite was as high as 82.86 W/(m·K) which was almost 1.5 times of PAN-CF/epoxy composites, and the through-thickness thermal conductivity with the value of 2.54 W/(m·K) also increased by 65%. The introduction of PBO macromolecules could contribute new conductive paths and alleviate the problem of interfacial temperature gradients between CF and resin matrix. As a result, thermal conductivity properties of coaxial PAN/PBO-CF reinforced composites significantly improved. [ABSTRACT FROM AUTHOR]

Abstract: To investigate the effect of γ-ray radiation on the microstructure of carbon fibers (CF) and graphite, the carbon fibers and graphite were irradiated by 60Co source at room temperature. X-ray diffraction results indicate that the interlayer spacing d 002 of CF and graphite decreased after irradiation. The intensity of (002) peak in CF decreased while the peak of the (002) plane in graphite becomes sharper after irradiation. Scanning electron microscopy combined with energy dispersive X-ray spectroscopy determines that γ-ray irradiation slightly improves the carbon content of CF surface layer. Compton scattering effect and heating caused by γ-ray are proposed to be responsible for the graphitization of CF and graphite. [Copyright &y& Elsevier]

• The photoswitchable MOF were anchored on CF surface via layer-by-layer method. Metal-organic frameworks (MOFs) are promising candidates for improving the interfaces of composite materials. In this work, we build MOF on a carbon fiber (CF) surface by using a layer-by-layer approach in situ. The results reveal that the MOF are constructed on the surface uniformly with a nanosheet-like structure. MOF make a significant contribution to the interfacial shear strength (IFSS) and surface energy, which were increased by 70.30% and 69.75%, respectively. The tensile strength of functionalized CF do not show an obvious decrease. After loading epoxy as guest molecular into the MOF, the functionalized CF present the ability for healing the interface and the first healing efficiency is 97.01%. In the future, the functionalized CF have the potential to apply in composites with remote-control self-healing. [ABSTRACT FROM AUTHOR]

In order to comprehend the influence of different "rigid-flexible" structures on the interface strength of carbon fiber(CF)/epoxy composites, CNTs was firstly chemically grafted on CFs surface, and then polyamide (PA) was grafted onto CF-CNTs surface through varying anionic polymerization time of caprolactam [ CF-CNTs-PA n (n = 6 h, 12 h, 24 h)]. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy indicated the successful establishment of CNTs and PA. TGA demonstrated the different grafting amounts of CF-CNTs-PA n (n = 6 h, 12 h and 24 h). SEM images revealed a compactness and uniform coverage of the CNTs/PA, with increasing polymerization time, the CF and CNTs surface was covered by a thick layer of PA. The surface energy increased and then decreased. The optimal interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) of the CF/epoxy composites with a polymerization time of 12 h (CF-CNTs-PA 12h) was 86.7 and 85.4 MPa, which was 77.6% and 45.7% higher than that of untreated CF/epoxy composite. As the polymerization time grew, the impact toughness and tensile strength of CF/epoxy composites enhanced and conductivity of CF/epoxy composite reduced. In addition, the mechanisms of reinforcement and toughening were also illuminated. This work would provide a certain theoretical basis for the preparation and applications of high-performance CF composites with different structures. [ABSTRACT FROM AUTHOR]

Abstract Performance of carbon fiber (CF) reinforced composites mainly depends on the tensile strength and interfacial bonding strength between fiber and the matrix. However, most of the surface modification technologies for CF may result in decrease in its tensile strength in both laboratory scale and commercial production. Herein, carbon black (CB) was decorated onto the surface of CF by chemical vapor deposition (CVD) method. SEM, TEM and AFM characterizations showed that CB significantly changed the morphology of CF. The results of dynamic contact angle text (DCAT) demonstrated that the surface energy of CF was increased due to the loading of CB. Upon the decoration by CB, IFSS, ILSS and impact strength of CF/epoxy composites were enhanced, corresponding to 46.84%,29.11% and 48.24%, respectively, and the reinforcing and toughening mechanisms have also been discussed. Besides, the results of tensile tests for single fiber showed that the tensile strength (TS) of CB-decorated CF was higher compared with that of original CF. Meanwhile, this modification method for CF could serve as a basis for realizing the industrialization online production. [ABSTRACT FROM AUTHOR]

As an important material candidate for automotive, aviation, and aerospace, the wide application of carbon fiber-reinforced epoxy resin composites (CFRPs) was important. However, restricted by the low toughness. Herein, octaaminopropyl cage polysilsesquioxane-polyurethane prepolymer (POSS-PU) was synthesized by in-situ polymerization of PU on the POSS, and then employed as the modifier for epoxy resin (EP). Compared to pristine EP, the toughness of the 7.5 wt% POSS 0.5 -PU/EP was increased by 115.3 % without compromising the tensile strength and T g. The unnotched impact strength, interlaminar shear strength (ILSS), and flexural strength of the CFRPs prepared from the modified EP were increased by 73.5 %, 7.5 %, and 42.4 %, compared to CF/EP. Additionally, the mechanical properties of CFRPs maintained a substantial improvement under low-temperature, and the CF/7.5 wt% POSS 0.5 -PU/EP was increased by 72.9 % (impact strength) and 21.7 % (ILSS), compared to those of CF/EP. Compared to the improvement in the toughness of CFRPs at room temperature, the retention rate of toughness enhancement at low temperature was approximately 100 %. CFRPs prepared by POSS x -PU/EP offered outstanding mechanical properties and hence showed great potential for future industrial applications. [Display omitted] • POSS-PU was prepared by in-situ polymerization, and uniformly dispersed in EP by physical blending. • POSS-PU greatly improved the toughness of the EP (115.3 %) without sacrificing strength and T g. • Compared to CF/EP, ILSS and impact strength of CF/7.5 wt% POSS 0.5 -PU/EP increased by 7.5 % and 73.5 %. • CF/7.5 wt% POSS 0.5 -PU/EP possessed the most outstanding cryogenic strength and toughness. • POSS x -PU/EP has excellent processability since its low consistency coefficient. [ABSTRACT FROM AUTHOR]

Abstract Carbon fiber composite laminates were interfacially reinforced through in-situ synthesis of g-C 3 N 4 on the carbon fibers. The introduced g-C 3 N 4 greatly improved the roughness, functional groups and wettability on the carbon fiber surface and markedly enhanced the interfacial properties of composite laminates. The surface free energy of carbon fibers was increased by 67.81%. Interlaminar shear strength and interfacial shear strength of composite laminates were increased from 51.84 to 72.09 MPa and 44.62–73.41 MPa, respectively. The significantly enhanced interfacial properties enabled the mechanical performance of composite laminates to reach a superior state. Tensile strength and bending strength were increased by 19.54 and 10.51%, respectively. The total absorbed energy of impact experiment was also enhanced from 1.14 to 1.78 J. Meanwhile, dynamic mechanical properties and hydrothermal aging resistance were also ameliorated significantly. The improved interfacial properties and mechanical properties were ascribed to the increased mechanical interlocking, enhanced chemical bonding and ameliorated wettability created by g-C 3 N 4. Graphical abstract Surface morphology of carbon fibers with g-C 3 N 4 and comparison of interfacial properties of carbon fiber composite laminates. Image 1 Highlights • Carbon fiber composite laminates were interfacially strengthened through in-situ synthesized graphitic carbon nitride (g-C 3 N 4). • The surface free energy of carbon fibers was increased by 67.81%. • Interlaminar shear strength and interfacial shear strength of composite laminates were increased from 51.84 to 72.09 MPa and 44.62–73.41 MPa, respectively. [ABSTRACT FROM AUTHOR]

Abstract A self-synthesized octa(γ-chloropropyl) polyhedral oligomeric silsesquioxanes (POSS) and its evolutionary amino-terminated hyperbranched structure were introduced onto the carbon fibers (CFs) surface (CF-G n -POSS-NH 2 , n = 1, 2 and 3) by chemically and successively grafting method to improve the interfacial properties of CFs/epoxy composite. The fiber surface structures could be tuned through regulating grafting generation (n) of CF-G n -POSS-NH 2 , and the polarity and roughness of CF surface increased with the incremental dendritic generation number. Interfacial shear strength (IFSS), interlaminar shear strength (ILSS) and dynamic mechanical properties of the functionalized CFs composites improved as the grafting generation increased, which may be attributed to the varying degrees of chemical interaction, mechanical interlocking and resin wettability provided by hyperbranched G n -POSS-NH 2 interface. Moreover, the interfacial structure has been also speculated and analyzed. [ABSTRACT FROM AUTHOR]

Abstract In-situ synthesis of C 3 N 4 on the carbon fiber surface was reported for enhancing interfacial properties of carbon fiber reinforced epoxy resin composite. The formed C 3 N 4 on the carbon fiber surface can greatly increase the roughness, polar functional groups and wettability of carbon fiber surface, thereby leading to significant enhancement of interfacial properties of composites. After modification, interlaminar shear strength (ILSS) and interfacial shear strength (IFSS) of carbon fibers composites are increased from 44.3 to 60.7 MPa and from 43.1 to 75.9 MPa, respectively. Moreover, the surface free energy of carbon fibers is increased by 65.6%. The improved interfacial properties endow carbon fiber composites with better mechanical properties, leading to an increased tensile strength of composites from 1063 to 1279 MPa and total absorbed energy of impact experiment from 1.22 to 1.75 J. Meanwhile, the dynamic mechanical properties and hydrothermal aging resistance are also enhanced significantly. The storage modulus increases from 64.3 to 74.1 GPa. The markedly enhancement of interfacial mechanical properties and mechanical properties could be attributed to the improved resin wettability, enhanced mechanical interlocking and increased chemical bonding induced by the existence of C 3 N 4 on the carbon fiber surface. [ABSTRACT FROM AUTHOR]