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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]

The epoxy resin was modified by hyperbranched structure of hydroxyl terminated to obtain waterborne epoxy resin for using as the carbon fiber (CF) sizing agent. By mixing method of waterborne epoxy resin and water, the waterborne epoxy sizing agent can be fabricated directly. In the sizing process, free of volatile organic solvents ensure the safety of operators and environment. Moreover, the introduction of tertiary amine group in hyperbranched structure will promote the reaction between epoxy and hydroxyl groups, and thus enhance the bonding strength between CF and epoxy resin. Results showed that the introduction of sizing agent does not sacrifice the CF single fiber tensile strength. The structure of epoxy resin retained in sizing agent is beneficial to the good wettability between CF and epoxy resin according to surface energy results. Interfacial shear strength value increases from 51.75 to 72.34 MPa, and interlaminar shear strength value increases from 80.32 to 90.34 MPa. These mechanical properties show that hyperbranched epoxy resin sizing agent with a large amount of hydroxyl groups can effectively improving the interface adhesion between CF and epoxy resin, showing a broad application prospect in composite materials field. [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]

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]

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]

To improve the interfacial properties in carbon fiber (CF)-reinforced unsaturated polyester (UP) composites, we directly introduced functionalized carbon nanotubes dispersed in the fiber sizing onto the fiber surface. For comparing the influence of polymer type on sizing effect, two different polymers (UP MR13006 and water-soluble epoxy (EP)) were used to prepare sizing agent. Morphology and surface energy of CFs were examined by scanning electron microscopy and dynamic contact angle analysis test. Tensile strength was investigated in accordance with ASTM standards. Mechanical properties of the composites were investigated by interlaminar shear strength (ILSS) and impact toughness. Test results indicate that TS, ILSS, and impact toughness were enhanced simultaneously. For UP matrix, the sizing agent containing UP has better reinforcing and toughening effect than the sizing agent containing water-soluble EP. [ABSTRACT FROM PUBLISHER]

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: 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 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: Co60 γ-ray irradiation as a novel method for modification of carbon fiber (CF) surface was introduced in this paper. After surface treatment by mutual irradiation the interlaminar shear strength (ILSS) of CF/epoxy composites was enhanced by about 37%. Surface elements of CF were determined by XPS analysis, which indicated that the oxygen/carbon ratio increased rapidly. Fitting the C 1s spectra demonstrated that two new photopeaks were emerged which was indicated h name="dbnd" />O and plasmon, respectively. Surface topography of carbon fibers was analyzed by atomic force microscopy (AFM). It could be found that the degree of surface roughness was increased by lower absorbed dose (30kGy), but excessive irradiation (>250kGy) was not beneficial for mechanical interlocking between CF and epoxy resin. The impregnating performance of CF was also improved after irradiation. [Copyright &y& Elsevier]

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]

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: 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]

• 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]

A novel amine-based functionalization method was developed to improve the interfacial adhesion between TiO 2 NWs and CFs in supercritical water. The microstructure, morphology and mechanical properties of CFs were investigated. It was found that introducing hexamethylenetetramine (HMTA) dendrimers and branched polyethyleneimine (PEI) on CF could increase significantly the adhesion strength between CF and TiO 2 NWs and their interfacial shear strength with epoxy resin, and the order is CF-PEI-TiO 2 NWs > CF-HMTA-TiO 2 NWs > CF-COOH-TiO 2 NWs > CF-TiO 2 NW. Meanwhile, the reinforcing mechanisms and interfacial failure modes have also been discussed. We believe that these effective methods may provide theoretical foundation for the preparation of high performance composite materials. [ABSTRACT FROM AUTHOR]

An effective method for bonding carbon nanotubes (CNTs) onto carbon fibers (CFs) surface via layer-by-layer (LBL) grafting method is reported here. The CNTs have been chemically grafted as confirmed by X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) indicates that this LBL method can increase the dispersion quality of the CNTs on CF surface. The polarity, wettability and roughness of the CFs have been significantly increased after the CNTs modifying. The interfacial shear strength (IFSS) and impact strength test suggest that the hierarchical structure can result in a remarkable improvement for the interfacial properties. The results also indicate that this LBL method is a promising technique to modify CFs with the high interfacial performance. [ABSTRACT FROM AUTHOR]

Most of the surface modification technologies for carbon fibers, no matter in laboratory scale or for commercial manufacture, are accompanied by a simultaneous decrease in tensile strength. In this paper, a feasible and high efficient strategy for carbon fiber treatment which could obviously improve both tensile strength and interfacial adhesion was proposed. Continuously moving carbon fibers were treated with atmospheric helium plasma for 1 min, followed by a 5 min pyrolytic carbon deposition using ethanol as precursor at 800 °C. The effects of the new approach were characterized by SEM, AFM, nanoindentation, XPS, Raman, wettability analysis, single fiber tensile strength testing and single fiber pull-out testing. After modification, pyrolytic carbon coating was deposited on the fiber surface uniformly, and the roughness and surface energy increased significantly. The single fiber tensile testing results indicate that the resulting fiber strength increased 15.7%, rising from 3.13 to 3.62 GPa. Meanwhile, the interfacial shear strength of its epoxy composites increased from 65.3 to 83.5 MPa. The comparative studies of carbon fibers modified with commercial anodic oxidation and sizing were also carried out. The results demonstrate that the new method can be utilized in the carbon fiber manufacture process and is more efficient than the traditional approaches. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced composites have been attracting increasing attention due to their excellent mechanical properties. However, the interfacial properties of carbon fiber composites tend to be weak because carbon fibers naturally show a weak wettability and adsorption with most polymers matrix. Here, we proposed a method to improve the interfacial properties of carbon fiber composites together with the tensile strength of carbon fiber. Briefly, a layer of graphene oxide (GO) was deposited on continuous carbon fibers by electrophoretic deposition in isopropyl alcohol under ultrasonic treatment. After treatment at 150 °C, the tensile strength of carbon fibers and the interfacial shear strength (IFSS) of carbon fiber/epoxy composites were enhanced by 34.58% and 69.87%, respectively. This method is believed to have applications in continuous production of high-performance carbon fiber composites. [ABSTRACT FROM AUTHOR]

Using molten urea as the solvent, carbon fibers were functionalized with carboxylic acid groups via aryl diazonium reaction in 15 min to improve their interfacial bonding with epoxy resin. The surface functionalization was quantified by X-ray photoelectron spectroscopy, which showed that the relative surface coverage of carboxylic acid groups increased from an initial percentage of 3.17–10.41%. Mechanical property test results indicated that the aryl diazonium reaction in this paper could improve the interfacial shear strength by 66%. Meanwhile, the technique did not adopt any pre-oxidation step to produce functional groups prior to grafting and was shown to maintain the tensile strength of the fibers. This methodology provided a rapid, facile and economically viable route to produce covalently functionalized carbon fibers in large quantities with an eco-friendly method. [ABSTRACT FROM AUTHOR]

Fibrous carbon materials have been attracted many researchers' attentions. Carbon fibers have been developed as one of the most important industrial materials for modern science and technology since 1960s [1] . Due to the superior mechanical properties including high-specific strength and modulus, low density and thermal expansion, heat resistance, and chemical stability, carbon fibers as reinforcement materials have provided the impetus for researchers in developing high-performance composite materials. Nowadays, carbon fiber reinforced plastics (CFRP) are widely applied in the industries of aeronautic, aerospace, sporting goods, as well as new energy. The region between the fibers and matrix, contains unique micromechanical properties, is characteristically called the interphase and influence the bulk composite properties. Interface between fibers (reinforcements) and matrix is an important component for CFRP which may govern the CFRP performances [2] . For example, the interphase determines the off-axis strength and impact toughness of CFRP, environmental stability of CFRP and functional performance of CFRP. The effect of interface on composite can be achieved by regulating the composition, structure and distribution of the interface [3] . It has been proved that there has an optical interface for polymer based composite through the match of composite interface, reinforcement and polymer matrix. However, in terms of the smooth surface and chemical inertness of carbon fiber, the interface between carbon fiber and resin matrix is unsatisfactory. The interface should be modified and carefully controlled, which can be through by increasing the surface polarity of carbon fiber, improving the wettability between carbon fiber and resin, as well as promoting the chemical reaction. Obey these principles, the interfacial modification methods have been well developed. The universality of carbon fiber and polymer matrix, and the variability of the composite material forming process result in the complexity of polymer-based composites interface problems. Meanwhile the scale of the interface region is very small, it has great difficulty in characterizing the chemical structure, physical properties and mechanical characteristics. Recently, a series of effective characterization methods have been developed and initial interface characterization system is always being improved. With interface characterization techniques, the interfacial composition, structure morphology and micro-mechanical characteristics of interface can be researched easily, which can provide the basis for studying the interface physical and chemical properties. Hence interface characterization techniques not only are theory researches, but also have important practical significance for solving practical application problems of carbon fiber composites. Interface characterization techniques have become an important research direction of interface engineering research. In this paper, the researches in this field of carbon fiber interface were described, such as carbon fiber composite material characterization methods, interface control, and interfacial modification methods. With reference to the research achievements of a large number of scholars at present, so their current development trend were systemic concluded. [ABSTRACT FROM AUTHOR]

A novel supercritical method for deposition of polyethyleneimine (PEI) onto carbon fibers (CFs) surface was reported. The surface functional groups, morphology, wettability and interphase properties of CFs grafted with PEI (CF-g-PEI) were studied, and compared to physically-adsorbed and chemically-adsorbed ones (CF-c-PEI and CF-ad-PEI). The CF-g-PEI exhibited the highest deposition amount and interfacial adhesion strength. Interface enhancement mechanism and failure mode have also been explored in details. However, impact resistance and single fiber tensile strength of CF-g-PEI were not optimal. Hence, based on different applications, a property balance of the resulting composite should be considered. [ABSTRACT FROM AUTHOR]

Highlights: [•] A new chemical grafting method for carbon fibers was proposed. [•] The oxidation system adopts K2S2O8 and AgNO3. [•] The interfacial shear strength (IFSS) of carbon fiber increased by 61%, and the interfacial adhesion increased with dendritic generation number. [•] The tensile strength of carbon fiber does not decrease distinctly. [•] The treatment conditions are mild and convenient. [ABSTRACT FROM AUTHOR]

Abstract: In order to improve the interfacial properties between carbon fibers and epoxy matrix, supercritical water and hydrogen peroxide were used as oxidation medium for the oxidation treatment for carbon fibers. Analysis results of X-ray photoelectron spectroscopy suggest that the oxygen content on the carbon fibers’ surfaces increases by these oxidation treatments. Scanning electron microscope and atomic force microscopy images indicate that the surface appearance of oxidized carbon fibers obviously changed. The maximal interlaminar shear strength and interface shear strength of carbon fiber/epoxy resin composite in which the fibers were treated by the supercritical water and hydrogen peroxide systems reaches 70.46MPa and 106.66MPa, increases by 13.4% and 29.6% respectively compared with untreated carbon fibers. [Copyright &y& Elsevier]

Abstract: The polyacrylonitrile-based (PAN-based) carbon fibers with progressive amounts of the oxidation treatment have been investigated using a number of surface analytical methods. The chemical content and structure of oxidated fibers have been interrogated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM), then compared to the untreated ones. The value of oxygen content increased from 4.71% to 18.84%, meanwhile, the grooves on the surfaces of the carbon fibers were deepened gradually after treatments. The results of dynamic contact angle (DCA) measurements suggest that the increase in carbon fiber surface tension is mainly because of the polar component of surface tension. After treated with increasing amounts of oxidants, the monofilament tensile strength decreased less than 3.1%. [Copyright &y& Elsevier]

Carbon Fiber-Reinforced Polymers (CFRPs) with higher strength and toughness are indispensable to meet the demand from the rapid advancing industry sectors such as automotive, aviation, and aerospace. A novel "soft-rigid" interface layer was designed via a mild and facile self-assembly strategy to achieve simultaneous improvement for strength and toughness. The positively charged polyethyleneimine (PEI), and negatively charged nano-complex composed of metal-organic framework (UIO-66) and graphene oxide (GO) were assembled on carbon fibers (CFs) through electrostatic interaction. The results shown that the roughness and wettability on the fiber surface were significantly improved by fiber surface modifications. Compared with the composite using pristine CFs as reinforcement, the interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) of the composite with the "soft-rigid" interface phase were improved by 42.12% and 23.07%, respectively. Besides, the debonding and fracture surface of CFRPs after treatment showed improved interface performance. Moreover, the impact toughness of the composite was improved from 60.24 kJ/m2 to 89.38 kJ/m2. [Display omitted] • A novel "soft-rigid" interface layer was constructed via electrostatic assembly. • The interfacial strength and toughness of composites were improved simultaneously. • The nano-coupling interaction that essential for interface performance was proposed. [ABSTRACT FROM AUTHOR]

The interfacial interaction between carbon fibers (CFs) and resin matrix is an important factor affecting mechanical performances of CF-based composites. In this work, a new approach combining electrodeposition method (EDM) and "Ag–S″ bonds was applied to fabricate functional CF-based composites while preserving the mechanical properties of CFs. Silver nanoparticles were first attached on the CF surface by EDM. Then 4-aminothiophenol or 4-mercaptobenzoic acid was linked to Ag surface by Ag–S bonds to incorporate different functional groups onto the fiber surface. The interfacial shear strength was improved pronouncedly while the tensile strength was maintained consistent. The interfacial shear strength of the CFs after functionalized was increased 21.10% and 32.04%, respectively. However, the tensile strength of them decreased no more than 3%. With improved properties, these nanocomposites have potential applications for aerospace, transportation, electronics and other fields. [ABSTRACT FROM AUTHOR]