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Fourier transform infrared spectroscopy spectra of the untreated and electrochemical oxidation treated carbon fibers (CFs) as a function of current densities.
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In this work, we studied the effects of electrochemical oxidation treatments of carbon fibers (CFs) on interfacial adhesion between CF and epoxy resin with various current densities. The surface morphologies and properties of the CFs before and after electrochemical-oxidation-treatment were characterized using field emission scanning electron micro...
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... enhancing mechanical interlocking between CFs and epoxy resin, electrochemical oxidation treatment introduced oxygen-containing functional groups and thereby increased the surface polarity. Fig. 3 shows the FT-IR spectra of the = 50.42 mN/m, and = 0.38 mN/m, Donnet). Where g is the surface tension of the wetting liquide, is the dispersion com- ponent of the wetting liquide, and is the polar component of the wetting liquide. By using two testing liquids, the surface free energy of the CFs can be calculated according to the ...
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... It is assumed that the deep grooves formed along the fiber length direction via the electrochemical oxidation treatment became shallow owing to the surface etching. According to previous studies, etching proceeds with electrochemical oxidation, thereby changing the diameter and decreasing the strength of the carbon fiber [23]. In this study, as the carbon fiber diameter did not change significantly after electrochemical oxidation, it can be inferred that etching did not proceed excessively. ...
... Figure 7 shows the tensile properties of single carbon fibers and the IFSS of untreated and surface-treated carbon fibers. The tensile strength of EO-CF is lower than that of AS-CF because chemical etching during electrochemical oxidation damaged the surface structure of the carbon fiber [23]. However, after silane treatment, the tensile strength of EOS3-CF increased by approximately 21% compared to that of AS-CF. ...
The interfacial adhesion between carbon fibers (CFs) and a thermoplastic matrix is an important aspect that should be improved in manufacturing CF-reinforced thermoplastics with high strength and rigidity. In this study, the effects of a two-step surface treatment comprising electrochemical oxidation and silane treatment of the CF surface on the mechanical properties of CF/maleic anhydride-grafted polypropylene (MAPP) composites were confirmed. The surface characteristics of the treated CFs were analyzed via scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The tensile testing of a single CF and interfacial adhesion of the samples before and after the surface treatment were analyzed using a single-fiber testing machine and a universal testing machine. After the silane treatment, the roughness of the CF surface increased due to the formation of a siloxane network. In addition, the interfacial shear strength increased by ∼450% compared to that of the untreated CFs due to the covalent bond between the -NH2 end group of siloxane and MAPP. This two-step surface treatment, which can be performed continuously, is considered an effective method for improving the mechanical interface strength between the CF and polymer matrix.
... Carbon fiber (CF) is a lightweight material that has a high specific strength, stiffness, thermal conductivity, and electrical conductivity compared to other materials, as well as high corrosion resistance and chemical resistance [1][2][3][4][5]. However, since CF is an expensive material, it is applied only to expensive components such as those associated with aviation, space, wind power, sports cars, and sporting goods, and environmental problems such as disposal of carbon composites in landfills after use remain a challenge that must be solved [6]. ...
... In general, surface treatment includes wetting methods (liquid oxidation) such as sulfuric acid and nitric acid [14][15][16][17][18][19][20][21], dry methods (dry gaseous oxidation) [22][23][24][25][26][27][28][29] such as high-temperature treatment in an atmosphere of oxidizing gas or inert gas, electric oxidation methods [3,[30][31][32], the plasma method [33][34][35][36][37][38][39] of surface treatment using ionized gas, and exposure to strong energy such as ozone and ultraviolet rays (energetic ions oxidation) [40][41][42]. ...
... In the case of heat treatment at 300 • C in a nitrogen atmosphere, it has been reported that the polar free energy decreases due to the reduction of oxygen functional groups resulting from the curing of sizing [26]. In addition, after the electrical oxidation treatment, it was confirmed that the polar free energy increased due to the increase in the surface area and the increase of C-O, C=O, and O=C-O by etching the surface of the CF [3]. From these results, it can be seen that the interfacial shear strength between the CF and the resin increases due to the increase in polar free energy resulting from the introduction of oxygen functional groups to the surface of the CF during surface treatment. ...
In this study, the chemical state change of recycled carbon fiber (rCF) surfaces and the mechanism of the oxygen functional groups according to nitric acid treatment at various times and temperatures were investigated to upcycle the carbon fiber recovered from used carbon composite. When treated with nitric acid at 25 °C, the carbon fiber surface demonstrated the same tensile properties as untreated carbon fiber (CF) for up to 5 h, and the oxygen functional group and polar surface energy of C–O (hydroxyl group) and C=O (carbonyl group) increased slightly compared to the untreated CF up to 5 h. On the other hand, at 100 °C, the tensile properties slightly decreased compared to untreated CF up to 5 h, and the amount of C–O and C=O decreased and the amount of O=C–O (lactone group) started to increase until 1 h. After 1 h, the amount of C-O and C=O decreased significantly, and the amount of O=C–O increased rapidly. At 5 h, the amount of oxygen functional groups increased by 92%, and the polar surface energy increased by 200% compared to desized CF. It was determined that the interfacial bonding force increased the most because the oxygen functional group, O=C–O, increased greatly at 100 °C and 5 h.
... Carbon fibres (CFs), mainly produced from polyacrylonitrile (PAN) fibres, exhibit remarkable mechanical, physical, and chemical properties, including high stiffness and strength, low density and high electrical and thermal conductivity, and strong chemical stability. Therefore, individual carbon fibres or carbon fibres combined with resins as composite materials are receiving a lot of attention for use in aerospace, automobile, marine, and military industries as well as in other industrial applications (for pressure vessels, windmills, civil engineering/construction-related uses, sports equipment, semiconductors, electrodes, etc.) [1][2][3][4]. Furthermore, with targeted surface modification with appropriate functional groups, they become effective ion-exchangers and adsorptive materials, with applications in environmental domains and also in pharmaceutical separation [5,6]. ...
... The latter is further improved by physical intermolecular bonding (van der Waals and hydrogen bond forces) [1]. The presence of carboxyl groups on the fibre surface increases their interfacial strength with the epoxy matrix, whereas the introduction of phenol hydroxyl groups on the fibres increases their hydrophilic character [3,8,9] and improves their wettability with a hydrophilic polymer matrix [10]. ...
... Among these approaches, electrochemical oxidation treatment is one of the most effective, allowing for better control of the extent of fibre oxidation by simultaneously reducing damage and enabling continuous processing [16][17][18]. The use of aqueous solutions of electrolytes is generally preferred in the electrochemical process, which has been widely applied in industrial manufacturing because it is comparatively mild, cost-effective, environmentally friendly, and energy-saving and offers easier control of the process parameters and oxidation extent [3,16]. Cyclic voltammetry has the advantage of applying oxidation-reduction cycles in sequence, allowing for progressive oxidation of the fibres. ...
The unknown oxidative surface treatment of commercial carbon fibres, which raises difficulties in their application and research, the trend today and in the future to develop graphite-like carbonaceous materials for unconventional applications (e.g. to produce graphene), and the necessity to recycle carbon fibre products, all are approached with appropriate methodology. The latter is based on the further treatment of commercial carbon fibres by cyclic voltammetry under various electrochemical conditions, including the entire range of electrolyte concentrations from dilute to very concentrated sulphuric acid, in the potential range of -3 V to + 3 V and backwards. Characterisation methods such as XPS, SEM/EDS, and the Boehm titration technique are used to determine the electron acceptor/donor groups created on the carbon fibres. Three types of treated carbon fibres in H2SO4 are distinguished, (1) 1%, 5%, and 30% w/w, (2) 60% w/w, and (3) 96% w/w H2SO4, whereas for the last both cases, the carbon fibres after the 3rd cycle of treatment are overoxidised, suggesting the beginning of a degraded structure. For each concentration of H2SO4 and for each cycle of treatment: C–OH, C-O-C ≫ HBS (hydrogen bridge structure) ≫ COOH ≫ C = O. The mechanisms and formation reactions of functional groups created on carbon fibres during cyclic voltammetry treatment are also discussed in depth. Depending on the numerous application directions of carbon fibres, representative materials, such as carbon fibres treated with defined electrochemical conditions and having a preferred structure, can be chosen.
Graphical Abstract
... In recent years, carbon fiber composites have expanded their application not only in the aerospace industry but also in all industrial fields due to their high tensile strength and rigidity, excellent thermal conductivity, and electrical conductivity [1][2][3][4][5][6][7][8]. However, despite these advantages, carbon fiber composites are applied to produce only expensive parts due to their high price [9], and they have problems of environmental pollution since they are mainly manufactured from thermosetting resin-based composite materials that are difficult to recycle. ...
... In general, the surface treatments of carbon fibers include a wet method (liquid oxidation) [16,[18][19][20][21][22] in which the surface is treated with an acid such as sulfuric acid or nitric acid, a dry method (dry gaseous oxidation) in which the surface is treated at a high temperature in an oxidizing gas or inert gas atmosphere [9,[23][24][25][26][27], electrochemical oxidation [4,7,28], a plasma method of surface treatment using ionized gas [29][30][31], or energetic ion oxidation that exposes them to strong energy such as ozone and ultraviolet rays [3,[32][33][34]. It is known that heat treatment, which is a dry method in the surface treatment methods of carbon fibers, changes the properties of the carbon fibers according to the change in the atmosphere, temperature, and treatment time [23,24]. ...
... Other previous studies have reported that when heat-treated to 300 °C in a nitrogen atmosphere, curing of sizing reduces oxygen functional groups and polar free energy [25], and when plasma is treated in an oxygen atmosphere, it increases the carbon fiber surface area and oxygen functional groups [29]. It was also confirmed that after the electrical oxidation treatment, the surface area was increased by etching the carbon fiber surface, and the polar free energy was increased through an increase in C-O, C=O, and O=C-O [7]. From these results, it was confirmed that when surface treatment was performed, the higher the oxygen content in the atmosphere, the more the oxygen functional groups increased, and the polar free energy increased. ...
In this study, carbon fibers were heat-treated in a nitrogen and oxygen atmosphere according to temperature to elucidate the mechanism of chemical state changes and oxygen functional group changes on the carbon fiber surface by analyzing the mechanical and chemical properties of carbon fibers. Carbon fibers before and after heat treatment were analyzed using FE-SEM (Field Emission Scanning), UTM (Universal Tensile Testers), XPS (X-ray Photoelectron Spectroscopy), and surface-free energy. In the nitrogen atmosphere, which is an inert gas, the tensile strength was equivalent to that of the virgin up to 500 °C but decreased to 71% with respect to the virgin at 1000 °C. Furthermore, as the temperature increased from room temperature to 1000 °C, the oxygen functional group and the polar free energy gradually decreased compared with the virgin. On the other hand, in the oxygen atmosphere, which is an active gas, the tensile properties were not significantly different from those of the virgin up to 300 °C but gradually decreased at 500 °C. Above 600 °C, the carbon fibers deteriorated, and measurement was impossible. The oxygen functional group decreased at 300 °C, but above 300 °C, among the oxygen functional groups, the hydroxyl group and the carbonyl group increased. Furthermore, the lactone group formed and rapidly increased compared with the virgin, and the polar free energy increased as the temperature increased.
... This small content of oxygen can be explained by partial oxidation on the carbon fiber surface or by the application of organic sizing agents [153,154]. The electrochemical oxidation of carbon fibers is often used to improve the adhesion of carbon fibers to an epoxy-based matrix in a fiber-reinforced composite material [155]. but with low values. ...
... This small content of oxygen can be explained by partial oxidation on the carbon fiber surface or by the application of organic sizing agents [153,154]. The electrochemical oxidation of carbon fibers is often used to improve the adhesion of carbon fibers to an epoxy-based matrix in a fiber-reinforced composite material [155]. The EDS spectrum taken from the carbon fiber fabric exhibits an increased amount of oxygen, with around 4 at-%. ...
This review supports an overview of selected high-performance fibers and functional fiber materials. A review of several properties and applications is given. For fiber materials and fabrics, microscopic images taken by scanning electron microscopy (SEM) are presented. As well as this, electron dispersive spectroscopy (EDS) is performed on the fiber materials and an overview of EDS spectra is presented. The features of SEM images and EDS spectra are discussed, especially with the aim of supporting people who are working in the field of fiber analytics. To support a complete view of both analytic methods—SEM and EDS—challenges and typical mistakes for SEM measurements on textiles are also described. Altogether, this review supports a useful overview of interesting high technology fiber materials and their investigation using the analytical methods SEM and EDS. Using these, material properties and their composition are presented and discussed. The composition of industrial fiber materials is investigated and discussed, as well as fiber treatments for the realization of functional fiber properties. Furthermore, it aims to support a helpful tool for fiber and textile analytics and identification.
Textiles. 2022; 2(2):209-251
Open Access: https://www.mdpi.com/2673-7248/2/2/12
... To further illustrate the chemical state of surface-treated CFs, some researchers have also quantified the hydrophilicity through measuring the contact angles of CFs [29]. Meanwhile, a single CF pullout test has been conducted to evaluate the mechanic performance of CFs with different surface microstructures [1,30,31]. These investigations have led to many significantly deepened understandings of the CF surface microstructure and behavior. ...
... Although all the above investigations have clearly indicated that strong polarization can alter the surface state of a CF, no effort has been made to look into the detailed electrochemical activity and surface morphology changes in particular, because most of the studies were simply aimed at improving the adhesion of CFs to their matrix materials [21,25,30,39]. However, in practice, CF may be strongly polarized if it is used as an electrochemical sensor or reinforcement for carbon fiber reinforced polymers (CFRPs) in a service environment with stray current densities [5]. ...
The electrochemical activity of a carbon fiber was characterized at different potentials in 3.5 wt.% NaCl solution, and the fiber cylindrical surface changed by polarization at different potentials was revealed by SEM, AFM, optical microscopy, FTIR spectroscopy, Raman spectroscopy, and XRD. The results showed that the carbon fiber exhibited different electrochemical activities at some polarization potentials; within a 3V potential range the anodic and cathodic polarization current densities stepped up by more than 5 orders of magnitude, and the carbon fiber (CF) surface dramatically changed with time. Strong anodic polarization appeared to facilitate the breakdown of C-C covalent bonds in the carbon fiber and enhance the amorphization of the fiber surface.
... Therefore, improving the interfacial property has always been a hot research spot in both academia and industry. Lots of work have been conducted to achieve this goal, mainly by modification of the CF surface, including surface oxidation (electrochemical oxidation [7][8][9], gas oxidation [10], acid oxidation [11,12] and plasma treatment [13,14]), surface coating (sizing agents [15,16] and organic functionalization [17][18][19][20]), chemical vapor deposition [21,22], surface whiskering [23][24][25] and multi-scale reinforcement based on nanomaterials [26][27][28][29][30]. ...
... However, the preparation of multi-scale reinforcement usually contains three or even more steps which are complicated and time-consuming [31][32][33], limiting the industrial production of the composites. Moreover, as the first step of multi-scale reinforcement preparation, CF surface oxidation would damage the mechanical property of the CF monofilaments, which has been confirmed in many articles [7,8,34,35]. Therefore, a relatively fast preparation method of multi-scale reinforcement without mechanical property sacrifice is necessary and significant. ...
A kind of carbon fiber/carbon nanotubes (CF/CNTs) multi-scale reinforcement was prepared by one-step dipping method, in which silane coupling agent (3-glycidyl ether oxy-propyl trimethoxy silane, KH560) was used as the bridge between CF and CNTs. Results showed that CNTs were uniformly coated onto CF surface, and the surface chemical activity, wettability and single fiber tensile strength of modified CFs were all improved significantly. More importantly, the interfacial shear strength (IFSS) of CF/CNTs reinforced epoxy composite, CF/CNTs composite, observed by SEM, showed good interface adhesion. It was also found that the silane coupling agent and CNTs would enhance the interfacial properties synergistically. Besides, the bridging effect of CNTs as the interfacial reinforcing mechanism for CF/CNTs multi-scale reinforcement composite was put forward. This special reinforcing mechanism may be as the guiding principle for CF surface modification and interfacial properties enhancement.
... CFs have lots of surface defects, formed as a result of the production technology selected by industries, namely, the thermo-oxidizing method [6]. Selected treatments affect the roughness, surface morphology, and the porosity of the fibres [7]. ...
Carbon Fibres (CFs) are widely used in textile-reinforced composites for the construction of lightweight, durable structures. Since their inert surface does not allow effective bonding with the matrix material, the surface treatment of fibres is suggested to improve the adhesion between the two. In the present study, different surface modifications are compared in terms of the mechanical enhancement that they can offer to the fibres. Two main advanced technologies have been investigated; namely, plasma treatment and electrochemical treatment. Specifically, active screen plasma and low-pressure plasma were compared. Regarding the electrochemical modification, electrochemical oxidation and electropolymerisation of monomer solutions of acrylic and methacrylic acids, acrylonitrile and N-vinyl pyrrolidine were tested for HTA-40 CFs. In order to assess the effects of the surface treatments, the morphology, the physicochemical properties, as well as the mechanical integrity of the fibres were investigated. The CF surface and polymeric matrix interphase adhesion in composites were also analysed. The improvement of the carbon fibre’s physical–mechanical properties was evident for the case of the active screen plasma treatment and the electrochemical oxidation.
... Among these, CF has drawn more attention in composite design where anisotropic high thermal conductivity, large mechanical load transfer, and light weight are desirable. However, the inertness of the CF surface and the difference in its surface energetics with polymers play a key role in the integrity and properties of the final multicomponent system [12][13][14][15]. Therefore, the challenge addressed here is to enhance the interfacial adhesion between the matrix and the filler using the proper interfaces to obstruct the boundary phonon scattering while buffering the electrical conductivity of CFs for a better and safer performance in electronic units. ...
The purpose of this study is to prepare boron nitride (BN)-coated carbon fibers (CF) and to investigate the properties of as-prepared fibers as well as the effect of coating on their respective polymer–matrix composites. A sequence of solution dipping and heat treatment was performed to blanket the CFs with a BN microlayer. The CFs were first dipped in a boric acid solution and then annealed in an ammonia–nitrogen mixed gas atmosphere for nitriding. The presence of BN on the CF surface was confirmed using FTIR, XPS, and SEM analyses. Polypropylene was reinforced with BN–CFs as the first filler and graphite flake as the secondary filler. The composite characterization indicates approximately 60% improvement in through-plane thermal conductivity and about 700% increase in the electrical resistivity of samples containing BN-CFs at 20 phr. An increase of two orders of magnitude in the electrical resistivity of BN–CF monofilaments was also observed.
... Nonetheless, bare CFs have poor adhesion to the matrices such as epoxy and nylon, because the carbonization of CFs at a high temperature could eliminate the polar elements in the original precursor materials [10], resulting in an inert surface. To improve the interaction between CFs and their matrices, functional groups have to be added to the surfaces of bare CFs via different approaches, such as chemical oxi dation [11][12][13][14][15], electrochemical oxidation [16][17][18][19][20], and plasma treatment [21,22], in which, the electrochemical technique is the most effective and economic one. Various electrolytes have been used in the electrochemical oxidation, including ammonium salt [16,17,20,23], nitric acid [19], and potassium nitrate [24]. ...
... Various electrolytes have been used in the electrochemical oxidation, including ammonium salt [16,17,20,23], nitric acid [19], and potassium nitrate [24]. After the electrochemical treatment, the concentrations of oxygen and nitrogen functional groups on the CF surface markedly increase [18][19][20], and the chemical bonding between the CF and the matrices be effectively enhanced [10,18,23]. Also, the CF surface roughness can increase due to the etching effect of the oxidation treatment [10], which is favorable in increasing the adhesion strength physically. ...
... Various electrolytes have been used in the electrochemical oxidation, including ammonium salt [16,17,20,23], nitric acid [19], and potassium nitrate [24]. After the electrochemical treatment, the concentrations of oxygen and nitrogen functional groups on the CF surface markedly increase [18][19][20], and the chemical bonding between the CF and the matrices be effectively enhanced [10,18,23]. Also, the CF surface roughness can increase due to the etching effect of the oxidation treatment [10], which is favorable in increasing the adhesion strength physically. ...
The electrochemical behaviors of carbon fiber (CF) affect not only its mechanical properties in the aggressive environment but also the long-term durability of metals in contact. This study for the first time investigated the different electrochemical behaviors of the two-dimensional cross-section and cylindrical surfaces of a CF. Two specially designed carbon fiber electrodes (CFE) were used to understand the carbon fiber electrochemical performance in a 3.5 wt% NaCl solution. The results show that the CF is two-dimensional anisotropic in electrochemistry, and the cross-section is two orders of magnitude more active than the cylindrical surface. The strong polarization caused damage to the carbon fiber, particularly on the exposed cross-section.
