Improving the interfacial properties of carbon fiber–epoxy resin composites with a graphene-modified sizing agent

We successfully prepared a graphene-modified carbon fiber (CF) sizing agent with good dispersity and stability by dispersing reduced graphene oxide (RGO) into an emulsion-type sizing agent. RGO was obtained by the reduction of graphene oxide (GO) with the help of gallic acid. The influence of the graphene-modified sizing agent on the interfacial properties of the CF–epoxy resin composites was investigated with microbond testing and the three-point bending method. The results show that optimized interfacial properties were achieved when the size of the modified graphene was less than 1 μm, the content of RGO was 20 ppm, and the pH value of the sizing agent was 10.5. The interfacial shear strength of the composites reached 92.3 MPa, which was 29.6% higher than that of the composites with unmodified CFs. Compared with commercial-CF-fabric-reinforced composites, the interlaminar shear strength of the composites treated with the RGO-modified sizing agent increased by 21.5%. Both the interfacial and interlaminar failure morphologies of the composites were examined with scanning electron microscopy (SEM). The results show that a large amount of residual resin adhered to the surfaces of the CFs treated with the RGO-modified sizing agent; this indicated good interfacial properties between the CFs and the resin matrix. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47122.     

Effect of surface oxygen content and roughness on interfacial adhesion in carbon fiber–polycarbonate composites

The effect of surface chemistry and rugosity on the interfacial adhesion between Bisphenol-A Polycarbonate and a carbon fiber surface subjected to surface treatment to add surface oxygen groups was investigated. The surface oxygen content of PAN based intermediate modulus IM7 carbon fibers was varied by an oxidative surface treatment. The oxygen content of the carbon fiber surface increased from 4 to 22% by changing the degree of surface treatment from 0 to 400% of nominal commercial surface treatment levels. The oxidative surface treatment also causes an increase in surface roughness by creating pores and fissures in the surface by removing carbon from the regions between the graphite crystallites. To decouple the effects of surface roughness and the surface oxides on the interfacial adhesion, the oxidized fiber surface was passivated via hydrogenation at elevated temperature. Thermal hydrogenation removes the oxides on the surface without significantly altering the surface topography. The results of interfacial adhesion tests indicate that an increase in the oxygen content of the fiber does not increase the fiber-matrix interfacial adhesion significantly. Comparing adhesion results between oxidized and hydrogen passivated fibers shows that the effect of the surface roughness on the interfacial adhesion is also insignificant. Overall, dispersive interactions alone appear to be the primary factor in adhesion of carbon fibers to thermoplastic matrices in composites.     

Fabrication and microwave absorption properties of magnetite nanoparticle–carbon nanotube–hollow carbon fiber composites

Absorbents with “tree-like” structures, which were composed of hollow porous carbon fibers (HPCFs) acting as “trunk” structures, carbon nanotubes (CNTs) as “branch” structures and magnetite (Fe₃O₄) nanoparticles playing the role of “fruit” structures were prepared by chemical vapor deposition technique and chemical reaction. Microwave reflection loss, permittivity and permeability of Fe₃O₄–CNTs–HPCFs composites were investigated in the frequency range of 2–18 GHz. It was proven that prepared absorbents possessed the excellent electromagnetic wave absorbing performances. The bandwidth with a reflection loss less than −15 dB covers a wide frequency range from 10.2 to 18 GHz with the thickness of 1.5–3.0 mm, and the minimum reflection loss is −50.9 dB at 14.03 GHz with a 2.5 mm thick sample layer. Microwave absorbing mechanism of the Fe₃O₄–CNTs–HPCFs composites is concluded as dielectric polarization and the synergetic interactions exist between Fe₃O₄ and CNTs–HPCFs.     

Application of the thermal energy storage concept to novel epoxy–short carbon fiber composites

For the first time, multifunctional epoxy–short carbon fiber reinforced composites suitable for thermal energy storage technology were developed. Paraffin microcapsules (MC) and short carbon fibers (CFs) were added at different relative amounts to an epoxy matrix, and the microstructural and thermomechanical properties of the resulting materials were investigated. Scanning electron microscopy images of the composites showed a uniform distribution of the capsules within the matrix, with a rather good interfacial adhesion, while the increase in the polymer viscosity at elevated CF and MC amounts caused an increase in the void content. Differential scanning calorimetry tests revealed that melting enthalpy values (up to 60 J/g) can be obtained at high MC concentrations. The mixing and thermal curing of the composites did not lead to breakage of the capsules and to the consequent leakage of the paraffin out of the epoxy matrix. The thermal stability of the prepared composites is not negatively affected by the MC addition, and the temperatures at which the thermal degradation process begins were far above the curing or service temperature of the composites. Flexural and impact tests highlighted that the presence of MC reduces the mechanical properties of the samples, while CF positively contributes to retaining the original stiffness and mechanical resistance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47434.     

Effect of particle morphology on viscoelastic and flexural properties of epoxy–alumina polymer nanocomposites

Nanocomposites were synthesised by dispersing two different types of alumina nanoparticles in epoxy matrix by ultrasonication. Alumina nanoparticles of two shapes, rod and spherical were selected to investigate the effect of particle morphology on viscoelastic and flexural properties of nanocomposites. Specific surface area of both the selected nanoparticles was kept in the similar range. Good dispersion of nanoparticles was observed through transmission electron microscopy. The addition of nanoparticles in epoxy had significant enhancement in the viscoelastic properties and moderate improvement in flexural properties of composites. Composites having alumina nanorods showed higher improvement both in storage modulus as well as in flexural properties in comparison to composites having spherical alumina nanoparticles. Efficacy of Mori-Tanaka method was explored in modelling storage modulus of nanocomposites. Assorted size of alumina nanorods based on particle size distribution was used to model composites with nanorods to see the effect of size assortment on storage modulus.     

Influence of Thrower–Stone–Wales defects on the interfacial properties of carbon nanotube/polypropylene composites by a molecular dynamics approach

A molecular dynamics (MD) simulations study is performed on Thrower–Stone–Wales (TSW) defected carbon nanotube (CNT)/polypropylene (PP) composites. We identify the degradation of the CNT and the improvement of the interfacial adhesion between the defected CNTs and PP molecules considering different CNTs with different numbers of TSW defects. By embedding the CNTs into a PP matrix, the effect of the TSW defects on the transversely isotropic elastic stiffness of polymer composites is calculated by MD simulations. Even if the TSW defects degrade the elastic properties of the CNTs, the transverse Young’s modulus and the transverse and longitudinal shear moduli of the composites increase due to the stronger interfacial adhesion between the defected CNTs and matrix, whereas the longitudinal Young’s modulus of the composites decreases. To elucidate the improved interfacial load transfer between the CNTs and the matrix, random polymer chain crystallization onto the surface of CNTs is simulated. The simulation shows that PP chains are wrapped more uniformly onto the surfaces of defected CNTs than onto the pristine CNT. The non-bond adhesion energy between the PP chains and the defected CNTs is greater than that between the PP chains and the pristine CNT.     

Effect of incorporation of hafnium diboride nanofibers on thermomechanical properties of carbon fiber–phenolic composites

Carbon fiber/phenolic (C/Ph) composites were modified with different weight ratios of hafnium diboride (HfB₂) nanofibers to apperceive thermomechanical properties of C/Ph–Hf nanocomposites. Mechanical properties, thermal stability, and ablation resistance of C/Ph–Hf nanocomposites were found to be optimum when the weight percentage of HfB₂ was equal to one. Maximum flexural strength and modulus were obtained with 118 MPa and 1.9 GPa for C/Ph–1%Hf nanocomposite, respectively. Increasing the proportion of HfB₂, by delaying the temperature of thermal degradation of nanocomposites, enhanced the thermal stability and residual of C/Ph–Hf relative to C/Ph in both nitrogen and air environments. In the oxyacetylene flame test at 2500°C for 160 s, the optimum mass ablation rate of C/Ph–1%Hf nanocomposites was found to be 0.0150 g/s compared to 0.068 g/s for blank C/Ph, along with reducing the back surface temperature by 51%. The ablation mechanism of C/Ph–Hf nanocomposites after the oxyacetylene torch test was concluded from the derivations obtained from X-ray diffraction, energy dispersion spectroscopy, and microstructure analyses. These clarified that the formation of high-temperature species, such as HfO₂, HfC, and B₄C owing to oxidation of HfB₂ and subsequent reaction products with char, resulted in an increased ablation resistance of the nanocomposites.     

The effect of catalyst and heat treatment on the properties of carbon–metal composites

Carbon gel and carbon–nickel–palladium doped gels (C–Ni–Pd) were prepared by carbonising resorcinol–formaldehyde (RF) hydrogel and resorcinol–formaldehyde–nickel–palladium (RF–Ni–Pd) hydrogels at 900 °C in a nitrogen atmosphere. RF and RF–Ni–Pd hydrogels were synthesized through sol–gel polycondensation followed by ambient drying. The aim of this study was the determination of the effect of heat treatment in air at 450 °C on the properties of C–Ni–Pd gels prepared using different Pd salts. In the present work, Ni was added as acetate whereas Pd was added as acetate (CA–Ni–Pd) and as chloride (CB–Ni–Pd). Samples were examined by scanning electron microscopy and X-ray diffraction. Surface area was characterized by N₂ adsorption at ?195.5 °C. Thermogravimetric analysis was carried out in order to determine the thermal characteristics of carbon gel and nickel–palladium composites in air atmosphere. CA–Ni–Pd composite had a higher activity and two-phase reaction compared to the CB–Ni–Pd composite. Further improvement of the electrolyte diffusion into the particles of nickel and palladium was obtained by oxidative thermal treatment. During this process a structural modification of the material took place, consequently leading to changes in the electrochemical properties of the composites.     

Effect of fiber architecture and density on the ablation behavior of carbon/carbon composites modified by Zr–Ti–C

Three carbon/carbon (C/C) composites modified by Zr–Ti–C, with different fiber architecture in preforms and the same density, were prepared using chemical vapor infiltration and reactive melt infiltration methods. Two other samples with the same architecture in preforms and different density were also fabricated by the same methods. Their ablation behaviors were examined by oxy-acetylene flame. The results showed that the samples with chopped web needled perform had better ablation resistance than that of the samples with needle-integrated and fine-weave pierced perform. In the models of ablation behaviors, the sealing time of pores and gaps on the ablated surfaces has been defined to indirectly estimate the ablation property. The analysis of models also indicated that high density of the composites and appropriate small diameter of bundles of carbon fibers led to the short sealing time and good ablation resistance of the C/C–carbide composites.     

Effect of carbon and oxygen on the high-temperature properties of silicon carbide–hafnium carbide nanocomposite fiber

The polymer-derived ceramics (PDCs) technique enables relatively low-temperature fabrication of Si-based ceramics, with silicon carbide fiber as a representative product. Polycarbosilane (PCS) has Si-C backbone structures and can be converted to silicon carbide. In the PDCs method, residual or excess carbon is generated from the precursor (C/Si ratio = 2 for polycarbosilane). Because of the non-stoichiometry of SiC, the physicochemical properties of polymer-derived SiC are inferior to those of conventional monolithic SiC. Herein, a silicon carbide-hafnium carbide nanocomposite fiber was optimized by crosslinking oxygen into the PCS fiber by regulating the oxidation curing time. During pyrolysis, carbothermal reduction, and sintering, carbon was removed by reaction with hydrogen and cross-linked oxygen. Non-destructive techniques (X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and high-temperature thermomechanical analysis) were used to investigate the effects of excess carbon. The microstructure of the near-stoichiometric SiC-HfC nanocomposite fiber was more densified, with superior high-temperature properties.     

Growth of carbon nanotubes on the surface of carbon fiber using Fe–Ni bimetallic catalyst at low temperature

This article provides a method for growing carbon nanotubes(CNTs) on carbon fibers(CFs) using iron and nickel as catalysts at low temperatures. This series of experiments was conducted in a vacuum chemical vapor deposition(CVD)furnace. It is found that Fe–Ni catalysts, which have a certain thickness and can be better combined with resins when manufacturing composite materials, are more ideal for the growth of CNTs than single metal catalysts. At the same time, it is proved that the CVD process worked best at 450 °C. The mechanical property test proved the reinforcing effect of CNTs on carbon fiber, the single-filament tensile strength of CFs obtained by using Fe–Ni catalyst at 450 °C was 11% higher than that of Desized CFs. The bonding strength of carbon fiber and resin has also been significantly improved. When synthesized at low temperature, CNTs exhibited a hollow multi-wall structure.     

Improving tribological properties of phenolic resin/carbon fiber composites using m-Si3N4@PANI core–shell particles

Phenolic resin/carbon fiber (PF/CF) composites have good tribological properties; however, their extensive applications are limited because of the poor thermal conductivity of the phenolic resins. In this work, core‑shell particles of polyaniline-coated (3-aminopropyl) triethoxysilane-modified β-Si₃N₄ (m-SiN@PANI) were used to enhance the tribological, electrical, and thermal conductivity properties of a PF/CF composite. A core‑shell particle, consisting of m-SiN@PANI, was characterized by Fourier Transform Infrared Spectrometry, X-Ray Diffraction, Scanning Electron Microscope, and Transmission Electron Microscope. The friction, thermal, and electrical properties of the composites were characterized by multifunctional vertical friction testing, wear measurement testing, thermogravimetric analysis, thermal constant analysis, and electrical conductivity testing. Remarkably, the test results showed that compared with the wear surface of the PF/CF composite, that of the phenolic resin/(2.0 wt % m-SiN@PANI)/carbon fiber composite exhibited a smoother morphology. The results indicated that the addition of m-SiN@PANI effectively improved the thermal conductivity, electrical conductivity, friction coefficient, and wear rate of the composites, which were 3.164 Wm⁻¹ K⁻¹, 5.33 × 10⁻⁶ S/m, 0.1681 and 1.13 × 10⁻⁸ mm³/Nm, respectively. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47785.     

Effect of γ-ray irradiation grafting on the surface property and the bulk structure of M40J fiber

In this study, we aim to improve the surface property and bulk tensile property of M40J graphite fiber by γ-ray co-irradiation treatment of the fiber in epichlorohydrin/acetone mixed solution. The effect of the irradiation treatment was analyzed by X-ray photoelectron spectroscopy, atomic force microscopy, dynamic contact angle test, tensile test, short-beam shear test, scanning electron microscopy, and X-ray diffraction, respectively. The results indicated that the reactive activity, roughness, and interfacial adhesion property of the fiber were improved, and without destroying the bulk structure after the surface irradiation grafting treatment. Mechanical testing results indicated that the tensile strength was decreased slightly; however the tensile module was improved. The γ-ray co-irradiation grafting was an effective method for modifying the physicochemical properties of M40J graphite fiber and improving the interfacial adhesion of its composites.     

The influence of the core–shell structured meta-aramid/epoxy nanofiber mats on interfacial bonding strength and the mechanical properties of epoxy adhesives at cryogenic environment

The adhesives for adhesively bonded joints at cryogenic environment should be enhanced by reinforcement with low coefficient of thermal expansion (CTE) and high fracture toughness because the materials become quite brittle at cryogenic temperature. Aramid fibers are noted for their low CTE and have been used to control the CTE of thermosetting resins. However, aramid composites exhibit poor adhesion between the fibers and the resin because the aramid fibers are chemically inert and contain insufficient functional groups. In this work, core–shell structured meta-aramid/epoxy nanofiber mats were fabricated by electrospinning with polymer blending method to improve the interfacial bonding between the adhesive and the fibers under cryogenic temperature. The CTE of the epoxy adhesives reinforced with modified nanofiber mats was measured, and the effect on the adhesion strength was investigated at single lap joints at cryogenic temperature. The fracture toughness of the adhesive joints was measured using a double cantilever beam (DCB) test.     

Influence of quinone grafting via Friedel–Crafts reaction on carbon porous structure and supercapacitor performance

High specific surface area carbon has been modified with para-benzoquinone (p-BQ) via Friedel–Crafts reaction catalyzed by Iron(III) chloride followed by oxidation, in order to explore alternative strategies for obtaining high energy density supercapacitor materials by the combination of the double layer capacitance of carbons with the redox pseudocapacitance of the organic redox couple added on the carbon surface.Suitable structural and physicochemical characterization proved the formation of covalent bonds between carbon and p-BQ, and the electrochemical characterization showed a significant increase in gravimetric capacitance values after the addition of p-BQ which is maintained even after many cycles.This gravimetric capacitance increase was not only due to the redox reactions of p-BQ, but also to an increased double layer capacitance after p-BQ modification even when the BET surface area decreases after modification. A correlation with the pore structure of carbons showed that the increased double layer capacitance can be attributed to a better matching of carbon pore size with the size of electrolyte ions after p-BQ addition. Thus, this new addition strategy opens the way for the development of carbon-based materials for supercapacitors with higher energy densities coming from both increased pseudocapacitive reactions and increased double layer capacitance.     

Effects of carbon additives on the properties of ZrB2–based composites: A review

This review presents the recent achievements on carbon additives incorporated in ZrB₂ ceramics, improved properties, and their advancements. Monolithic ZrB₂ ceramics have broad potential applications, but their critical drawbacks such as poor damage tolerance, and weak oxidation and ablation resistance confines their applicability. It is an important issue to resolve these shortages in physiochemical properties by engineering the composite ingredients and process design of the ceramic counterparts for an extensive production and applications, which are especially essential in high–tech industries and products. Carbon additives have exceptional characteristics including low density, low cost, and excellent thermo–mechanical stability. These materials have been incorporated in ZrB₂ ceramics to enhance their efficiency and form practical composite ceramics. Although addition of the secondary carbonaceous phases is generally supposed to improve the mechanical properties of ZrB₂ composites, it may also result in a decrease in other aspects of performance, comparing with monolithic ZrB₂ ceramics. In this work, we reviewed the methods and strategies for the preparation of carbon modulated ZrB₂ ceramic composites. Moreover, the advantages, disadvantages, and the productivity of the introduced composite ceramics have been explored and featured.     

Study on interfacial interaction energy of Cu–SAM–epoxy systems in a hot and humid environment

Due to poor adhesion, the interfacial delamination is one of the typical failure modes in electronic packages. In this paper, two kinds of self-assembly monolayers (SAMs), SAMA and SAME, are added to Cu–epoxy interface and the effects of temperature, moisture, and cross-link conversion on the modified interfaces are investigated with molecular dynamics (MD) simulation. The results show that the interfacial interaction energy of the systems with SAMA increases with the increasing temperature, decreasing moisture content, and cross-link conversion. However, the interfacial interaction energy of the systems with SAME decreases with the increasing temperature and moisture content, while it is reluctant to the cross-link conversion. In addition, the simulation reveals that the covalent bonds between SAMA and epoxy enhance the interfacial adhesion of Cu–epoxy. However, the nonbond interactions of SAME and epoxy resin weaken the interfacial adhesion. This paper provides a new method for research and valuation the effects of SAM or other adhesive on interfacial adhesion. MD simulation is an efficient tool in predicting the performances of materials.     

Further studies on the use of Raman spectroscopy and X-ray diffraction for the characterisation of TiC-containing carbon–carbon composites

Raman spectroscopy and X-ray diffraction are used to study the crystalline structure of carbon–carbon and TiC-containing composites. The advantages and drawbacks of these techniques for the characterisation of carbon–carbon composites are analysed in the light of the distribution and arrangement of their components and the microstructural orientation of the supporting matrix. Analyses performed on longitudinal and transverse sections of the composites confirm that the measurements are affected by the orientation of the crystals. The overall crystalline parameters calculated by X-ray diffraction were unequivocally resolved for each single component by means of Raman spectroscopy. A significantly higher degree of order was observed in the TiC-containing matrix as a result of the catalytic graphitisation of the carbon achieved by the addition of titanium. In addition, Raman spectroscopy corroborated that the incorporation of TiC into the carbon matrix does not disrupt the orientation of the graphene planes of the matrix parallel to the fibre axis, a necessary characteristic for achieving an optimum heat transfer through the material.     

Effect of corona discharge on the stability of the adhesion of thin silicone-organic coating to polyamide fiber surface made by the sol–gel method

This paper presents the effect of pretreatment of polyamide (PA6) nonwoven with corona discharge on the stability of the adhesion of thin hydrophobic silicone-organic coating based on vinyltriethoxysilane, made by the sol–gel method. This pretreatment with corona discharge causes a change in the physicochemical properties of the PA6 fiber surface. These changes include, among others, an increase in the fiber surface roughness, wettability, and surface free energy. At the same time, XPS and EDS investigations have shown an increase in the degree of oxidation and the formation of functional polar groups on the fiber surface (C–O–, C–OH, and O=C–O–). As a result of the changes in the surface properties of pretreated PA6 fibers, a higher degree of the sol deposition was obtained compared with that for untreated nonwoven surface. The assessment of the stability of the adhesion of thin hydrophobic coating to the fiber surface was carried out on the basis of changes in the content of silica deposited on fibers and the kinetics of water contact angle after washing and abrasion processes. In the end, the PA6 nonwoven, pretreated with corona discharge, shows a higher stability of the adherence of the thin silicone-organic coating and a higher degree of hydrophobicity than the untreated nonwoven.