Untreated Carbon Fibers Research Articles

Modulating Carbon Fiber Surfaces with Vinyltriethoxysilane Grafting to Enhance Interface Properties of Carbon Fiber/Norbornene-Polyimide Composites.

In this study, vinyltriethoxysilane (TEVS) was introduced onto the surface of carbon fiber using liquid-phase oxidation and impregnation methods to incorporate vinyl groups onto the carbon fiber, thereby enhancing the chemical bonding between the carbon fiber and norbornene-polyimide (PI-NA). Through a systematic study of the hydrolysis conditions and concentration of the TEVS solution, the optimal modification conditions were determined. These conditions were used to graft TEVS onto the surface of oxidized carbon fiber to prepare carbon-fiber-reinforced PI-NA composites (CF/PI-NA). The results show that when carbon fiber was treated with a 0.4 wt% TEVS solution, the interlaminar shear strength (ILSS) of the composites reached 65.12 MPa, and the interfacial shear strength (IFSS) reached 88.58 MPa, representing increases of 27.58% and 35.62%, respectively, compared to the CF/PI-NA composite materials prepared from untreated carbon fiber. It is worth noting that the modification method described in the study is simple and easy to implement, and it has the potential for large-scale continuous production applications.

In situ growth of silver nanoparticles on carbon fiber by plasma–liquid interaction to improve performance of epoxy composites

Grafting nanomaterials on the carbon fiber (CF) surface is considered an effective strategy for enhancing the interfacial properties of CF-reinforced polymer composites (CFRPs). However, the mechanical properties of the CFs are often compromised during treatment. A new method for in situ growing silver nanoparticles (AgNPs) on the CF surface is proposed in this study. The CFs are first immersed in a low-viscosity silver nitrate solution to form a thin liquid film on the surface. Subsequently, using the abundant active particles in the plasma, the silver ions are reduced to silver atoms and grown into AgNPs on the CF surface. The tensile strength of CF@Ag was 38.74% greater than that of untreated CF, potentially due to the reparative action of AgNPs on defects in CF. The CF showed an evident improvement in surface wettability because of the AgNPs. Furthermore, the interfacial properties were noticeably improved, with the interfacial shear strength of CF@Ag increasing to 91.59 MPa, which was about twice that of pristine CF. Thus, the mechanical properties of composites are significantly improved (flexural strength increased by 190.74%). This study presents a non-destructive and convenient method for growing nanoparticles onto CF to establish a robust interface in CFRPs.

Collaboration of Fenton reaction with a tannin acid-based hyperbranched waterborne polyurethane sizing agent for synergistic enhancement of the CF/PA6 composite interfacial properties

The adhesive strength between the sizing agent and carbon fiber (CF) plays a pivotal role in determining the interfacial properties of composites. Unfortunately, this critical aspect has been consistently overlooked. In this study, a hyperbranched waterborne polyurethane (HWPU) sizing agent was prepared by biogenetic derived raw materials including gallic acid as well as tannic acid. Meanwhile, iron ion was introduced onto the surface of CF by Fenton reaction, forming a heterogeneous structure to elevate the mechanical interlocking between the CF and resin. Chelation of TA with iron ion on the fiber surface effectively enhanced the adhesion between sizing agent and CF. The mechanical properties of the newly designed composites were systematically investigated. The results showcase a significant enhancement in both flexural strength and interlaminar shear strength (ILSS) compared to untreated CF, marking improvements of 54.3% and 60.0%, respectively. Furthermore, the interfacial shear strength (IFSS) test exhibited a 71.2% augment. In conclusion, this approach presented a highly promising concept aimed at improving the interfacial performance of CF composite materials.

Effect of chemical oxidation process on adhesive performance in two component adhesive with nano particle and nano fiber additives

In the present study, chemically surface-treated nanoparticles and nanofibers were added to the adhesive to improve the performance of the two-component structural adhesive. In the study, DP460 structural adhesive was used as adhesive, functionalized Multi Walled Carbon Nanotubes (MWCNT-COOH) with COOH and carbon fiber (CF) chemically surface treated with HNO3 solution were used as nanostructures. In the experimental study, eight different parameters were investigated as the nanostructure was (i) undoped, (ii) 1 wt% MWCNT-COOH added, (iii) 1wt%. untreated CF added, (iv) 0.5 wt% chemically treated CF added, (v) 1 wt% chemically treated CF added, (vi) 2 wt% chemically treated CF added, (vii) 0.5 wt% MWCNT-COOH and 0.5 wt% chemically treated CF added, and (viii) 1 wt% MWCNT-COOH and 1wt% chemically treated CF added. According to the results of the study, adding nanoparticles to the adhesive increases the performance of the adhesive by about 12%, while adding nanofibers increases the performance of the adhesive by about 18%. In addition, increasing the inertness and wettability of nanofibers by chemical treatment, as well as the use of nanoparticles and fibers together, significantly increases the performance of the adhesive. In addition, the obtained results were supported by fourier transform infrared spectroscopy (FT-IR) analysis and scanning electron microscopic (SEM) analysis.

Growth of ZnO nanorods/flowers on the carbon fiber surfaces using sodium alginate as medium to enhance the mechanical properties of composites

The chemical inertness of the carbon fiber (CF) surface results in suboptimal mechanical properties of the prepared composites. To address this issue, we employed a combination of tannic acid and 3-aminopropyltriethoxysilane mixture (TA-APTES) grafted sodium alginate (SA) as a medium to enhance the interfacial properties of composites through the growth of ZnO nanoparticles on CF surfaces. ZnO nanolayers with rod-like and flower-like structures were obtained by adjusting the pH of the reaction system (pH = 10 and 12, respectively). Characterization results show that in comparison with the untreated CF composites, in the flexural strength, flexural modulus, interlaminar shear strength (ILSS) and interfacial shear strength (IFSS) of the as-prepared CF/TA-APTES/SA/ZnO10 (nanorods) composites were improved by 40.8 %, 58.4 %, 44.9 % and 47.8 %, respectively. The prepared CF/TA-APTES/SA/ZnO12 (nanoflowers) composite showed an increase in flexural strength, flexural modulus, ILSS and IFSS by 39.8 %, 63.6 %, 47.3 % and 48.2 %, respectively. These positive results indicate that the ZnO nanolayers increase the interfacial phase area and fiber surface roughness, thereby enhancing mechanical interlocking and load transfer between the fibers and resin matrix. This work provides a novel interfacial modification method for preparing CF composites used in longer and more durable wind turbine blades.

Reinforcement of carbon fibers: γ-irradiation induced microporous modulation and surface defect repairing with graphene quantum dots

Due to the presence of numerous defects both internally and on the surface, carbon fiber exhibits mechanical properties far below theoretical predictions. Finding a rapid and effective method for reinforcing the matrix remains a challenge. To address this, we have conducted structural reinforcement of carbon fiber by improving the orientation of internal micropores and eliminating surface defects. On the one hand, we subjected the carbon fiber to a dose of 100 kGy of gamma-ray irradiation in the air. After testing, the mechanical properties of the carbon fiber improved by 5.59%. Analysis using techniques such as small-angle x-ray scattering revealed that gamma rays can slightly alter the orientation of the fiber’s internal micropores and enhance graphitization to some extent. On the other hand, we introduced graphene quantum dots (GQDs) onto the surface of the carbon fiber using electrostatic spraying and electrophoretic deposition techniques to fill the defect sites. Compared to untreated carbon fiber, the mechanical properties improved by 10.65% and 9.40% when GQDs were grafted using electrophoretic deposition and electrostatic spraying methods, respectively. This improvement can be attributed to the adsorption of GQDs on the surface of the carbon fiber, which disperses stress during tensile loading and delays fracture. Finally, grafting of GQDs onto the surface of gamma-irradiated carbon fibers by electrophoresis improved the mechanical properties of the carbon fibers by 15.53% compared to unmodified carbon fibers. This work provides a more comprehensive perspective for repairing carbon fiber structures.

Synthesis and Application of Bimetal Decorated Plant-Based Carbon Nanomaterial for Hydrogen Storage

Abstract: In this study, carbon nanomaterials (CNMs) were synthesized from waste cotton fibers and examined their hydrogen adsorption capacity. The CNMs were created by subjecting waste cotton fibers to high-temperature pyrolysis at 800°C, followed by activation with alkali solution. Nano-sized metallic particles of Nickel and Aluminium were decorated on the activated carbon fibers. Analysis through SEM, EDAX, Raman spectroscopy, X-ray diffraction and BET surface area confirmed the porous nature and presence of metal particles in the CNMs. These materials exhibited a notably larger specific surface area (SSA) compared to untreated carbon fibers, enhancing their hydrogen storage capabilities as it showed 8.08 wt% of hydrogen adsorption using a Sievert's apparatus. This work, shows the promising potential of these CNMs for hydrogen adsorption in various industrial applications.

The Effect of Temperature on the Surface Energetic Properties of Carbon Fibers Using Inverse Gas Chromatography

This paper constitutes an original and new methodology for the determination of the surface properties of carbon fibers in two forms, namely, oxidized and untreated, using the inverse gas chromatography technique at infinite dilution based on the effect of temperature on the surface area of various organic molecules adsorbed on the carbon fibers. The studied thermal effect showed a large deviation from the classical methods or models relative to the new determination of the surface properties of carbon fibers, such as the dispersive component of their surface energy, the free surface energy, the free specific energy, and the enthalpy and entropy of the adsorption of molecules on the carbon fibers. It was highlighted that the variations in the London dispersive surface energy of the carbon fibers as a function of the temperature satisfied excellent linear variations by showing large deviations between the values of γsd (T), calculated using different models, which can reach 300% in the case of the spherical model. All models and chromatographic methods showed that the oxidized carbon fibers gave larger specific free enthalpy of adsorption whatever the adsorbed polar molecules. The obtained specific enthalpy and entropy of the adsorption of the polar solvents led to the determination of the Lewis acid–base constants of the carbon fibers. Different molecular models and chromatographic methods were used to quantify the surface thermodynamic properties of the carbon fibers, and the results were compared with those of the thermal model. The obtained results show that the oxidized carbon fibers gave more specific interaction energy and greater acid–base constants than the untreated carbon fibers, thus highlighting the important role of oxidization in the acid–base of fibers. The determination of the specific acid–base surface energy of the two carbon fibers showed greater values for the oxidized carbon fibers than for the untreated carbon fibers. An important basic character was highlighted for the two studied carbon fibers, which was larger than the acidic character. It was observed that the carbon fibers were 1.4 times more acidic and 2.4 times more basic. The amphoteric character of the oxidized fibers was determined, and it was 1.7 times more important than that of the untreated fibers This tendency was confirmed by all molecular models and chromatographic methods. The Lewis acid and base surface energies of the solid surface, γs+ and γs−, as well as the specific acid–base surface energy γsAB of the carbon fibers at different temperatures were determined. One showed that the specific surface energy γsAB of the oxidized fibers was 1.5 times larger than that of the untreated fibers, confirming the above results obtained on the strong acid–base interactions of the oxidized carbon fibers with the various polar molecules.

Preparation of CNTs/SCF reinforcement using multiple continuous surface treatments to achieve synergistic improvement of epoxy resin-based composites interfacial properties: Towards industrial production of carbon fiber surface treatment

The silane/maleimide co-modified waterborne polyurethane (WPU-M-S) sizing agent and furan-functionalized carbon nanotubes (CNTs-FA) were prepared through chemical modification method. The continuous grafting of carbon nanotubes (CNTs) was realized on the carbon fiber surface by multiple continuous surface treatments, including electrochemical anodizing (EAO), sizing, and chemical grafting of CNTs. The stable physical and chemical connection between carbon fiber, sizing agent, and resin was constructed through the preparation of CNTs/SCF reinforcement. The results of different surface treatment processes such as ultrasound and CNTs grafting process were contrastively studied in terms of surface morphology, microstructure, and mechanical properties. It is reflected that carbon fiber grafted with CNTs-FA (CNTs/SCF) that were prepared by ultrasound assisted chemical grafting provide optimal wettability and interfacial performance. The interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) of CNTs/SCF reinforced epoxy resin composites are 115.37 % and 93.91 % higher than those of the untreated carbon fiber (UCF), respectively. The synergistic improvement mechanism of reinforcement on carbon fiber reinforced epoxy resin composites interfacial properties was proposed. This research provides a multiple continuous surface treatment technology that matches the industrial production of carbon fiber to prepare CNTs/SCF reinforcement.

Bio‐inspired metal ion coordination cross‐linking synergistic strategy to enhance the interfacial properties of carbon fiber composites

AbstractThe application of carbon fiber (CF) in carbon fiber composites has faced limitations due to its surface chemical inertness. To overcome this challenge, this study draws inspiration from metal ion‐enhancing exquisite hierarchical and multiphase structures observed in biological materials. The research proposes a novel approach to enhance the interfacial bonding of CF/Epoxy (E‐51) composites by utilizing tannic acid (TA), carboxylated cellulose nanocrystals (CNCs), Fe3+ ions, and polyvinyl alcohol (PVA). This approach aims to create hydrogen bonding and metal synergistic networks on the surface of CFs through metal ion (Mn+) coordination cross‐linking synergistic (MCCS) interactions. Implementing MCCS strategy resulted in significant improvements in the mechanical properties of the hybrid reinforcements compared to untreated CF composites. The flexural strength, flexural modulus, interlaminar shear strength, and interfacial shear strength experienced respective increase of 50.9%, 72.8% 59.4%, and 61.9%. Moreover, the damping properties of the composites exhibited significant improvements. These positive outcomes can be attributed to the formation of chelation and dense hydrogen bonding networks between TA, Fe3+, CNC, and PVA. Furthermore, CNC and PVA formed cross‐linked nanolayers that effectively deflected cracks and facilitated high energy consumption at the interface. This proposed approach provides a sustainable, environmentally friendly, and efficient method for surface modification in the preparation of high‐performance fiber composites.Highlights Metal ion (Mn+) coordination cross‐linking synergistic strategy is proposed. Tannins/Fe3+/CNCs/PVA form multiphase nanolayers. Metal ion coordination cross‐linking enhances delicate multiphase structures. The prepared carbon fiber composites exhibit excellent properties. The as‐prepared carbon fiber composite has promising applications.

Enhanced Interfacial Properties of Carbon Fiber/Maleic Anhydride-Grafted Polypropylene Composites via Two-Step Surface Treatment: Electrochemical Oxidation and Silane Treatment.

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.

A novel bio-based hyperbranched waterborne polyurethane sizing agent with superior UV-resistance and interfacial properties for CF/PA6 composites

On account of environment concerns and the gradually depletion of fossil resources, a hyperbranched waterborne polyurethane (HWPU) serving for sizing agent of carbon fibers (CF) was designed based on bio-based materials. Hyperbranched chain extender named CAG was synthesized by citric acid (CA) and glycerol as HWPU precursor. Tartaric acid (TA) was coordinated with nano titanium dioxide (TiO2) through two –COOH groups, which was introduced to HWPU as the chain extender, leading to a significant improvement in ultraviolet (UV)-resistant of the sizing agent. The interfacial performance promotion of CF reinforced nylon 6 (CF/PA6) composites contributed by the HWPU sizing agent were systematically investigated. In contrast to the untreated CF composites, the mechanical performance arrived the best improvement after sizing by concentration of 1.5 wt%, which exhibited a dramatic promote of 44.9% in interlaminar shear strength (ILSS), 58.7% in interfacial shear strength (IFSS) and 43.3% in flexural strength. Extraordinary, the treated CF composites remained over 98% of mechanical performance after a week of unremitting ultraviolet irradiation, signifying the outstanding UV-resistance of the TiO2 modified HWPU sizing agent.

Construction of dendritic polymers on carbon fiber surfaces to improve the interfacial bonding of carbon fiber/silicone rubber composites

Carbon fiber (CF) reinforced composite materials are highly sought after for their exceptional mechanical properties and functional capabilities, making them promising materials for applications in aerospace and other industries. In this study, we aimed to construct a medium modulus interfacial layer using the layer-by-layer construction (LBL) method. This was achieved by grafting rigid dendritic polymers onto the surface of the carbon fiber, with the branch density being adjustable based on the reaction time. The rigid branched structure of the dendritic polymer and the numerous functional groups provide physical entanglement and stronger mechanical bonding at the interface, great chemical bonding. This distinctive structure improves the interfacial compatibility of the composite and enhances its mechanical properties. Following treatment, the tensile properties of the fibres are increased by approximately 20 %, suggesting that the treatment process effectively repairs surface defects on the fiber. Compared to untreated carbon fiber composites, the tensile properties of CF-M-P3 have improved by approximately 11 %. Furthermore, the thermal weight loss of the composite material is significantly reduced due to the branching of its rigid dendritic structure. The weight loss percentage decreased from 16.84 % to 7.89 % after being held at a temperature of 350 °C for a duration of 4 h.

Carbon Fiber Paper Sensor for Determination of Trimethoprim Antibiotic in Fish Samples.

The increase in anthropogenic pollution raises serious concerns regarding contamination of water bodies and aquatic species with potential implications on human health. Pharmaceutical compounds are a type of contaminants of emerging concern that are increasingly consumed and, thus, being frequently found in the aquatic environment. In this sense, an electrochemical sensor based on an unmodified and untreated carbon fiber paper (CPS-carbon paper sensor) was simply employed for the analysis of trimethoprim antibiotic in fish samples. First, the analytical conditions were thoroughly optimized in order for the CPS to achieve maximum performance in trimethoprim determination. Therefore, an electrolyte (0.1 M Britton-Robinson buffer) pH of 7 was selected and for square wave voltammetry parameters, optimum values of amplitude, frequency and step potential corresponded to 0.02 V, 50 Hz, and 0.015 V, respectively, whereas the deposition of analyte occurred at +0.7 V for 60 s. In these optimum conditions, the obtained liner range (0.05 to 2 µM), sensitivity (48.8 µA µM-1 cm-2), and LOD (0.065 µM) competes favorably with the commonly used GCE-based sensors or BDD electrodes that employ nanostructuration or are more expensive. The CPS was then applied for trimethoprim determination in fish samples after employing a solid phase extraction procedure based on QuEChERS salts, resulting in recoveries of 105.9 ± 1.8% by the standard addition method.

Investigating the Effects of Nitric Acid Treatments on the Properties of Recycled Carbon Fiber.

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.

Synergistic of anionic and nonionic monomers for high solid content bio-based waterborne polyurethane sizing agents

A high solid content bio-based waterborne polyurethane (WPU) was designed by combination of anionic and nonionic monomers, and serving as sizing agent for carbon fibers (CF). The electric double layer was formed by using bio-based tartaric acid (TA) and sodium lignosulfonate (SL) as donor of ionic groups and electrostatic repulsion was generated. Polyethylene glycol (PEG) was used to provide the hydrophilic segment of non-ionic monomer, which reduced the interfacial tension and improved the dispersion of emulsion. The synergistic effect of anionic and nonionic monomers promoted the stability of emulsion and the solid content of WPU sizing agent was arrived at 57%. The effect of sizing agent to the interfacial properties of carbon fiber reinforced nylon 6 (CF/PA6) composites were investigated. The flexural strength and interlaminar shear strength (ILSS) of the CF/PA6 composites exhibited the optimal performance at 1.5 wt% sizing concentration, revealing a considerably increase of 39.8% in ILSS and 38.5% in flexural strength as compared with untreated CF composites. This work contribute a fascinating method for further high solid content commercial production of environmentally-friendly WPU sizing agent.

Polyurethane with nano‐SiO2 based surface sizing method for 3D printed carbon fiber reinforced nylon 6 composites

AbstractContinuous carbon fiber reinforced polymer composite 3D printing has drawn more attention due to its ability to manufacture composite structures with complex shapes. The surface treatment of CF is necessary to improve the combination between carbon fiber (CF) and matrix. In this work, polyurethane with nano‐SiO2 (PU/SiO2) was used to size CF to enhance the compatibility of CF and nylon 6 (PA6). The chemistry and morphology of the CF were characterized by Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The interface strength between CF and PA6 was tested by the fiber pull‐out test, and eventually obtained optimized concertation of PU/SiO2 sizing agents (with 25 wt% PU and 0.4 wt% nano‐SiO2). The results show that compared with untreated CF, the interfacial shear strength (IFSS) of CF and PA6 after sizing increased by 316.93%. In addition, several CF/PA6 composite specimens printed by a homemade composite 3D printer were used to do mechanical tests. The results show that the flexural strength increased by 33.87%, the tensile strength increased by 20.75%, and the interlaminar shear strength (ILSS) increased by 66.54%.

Effect of electrophoretic deposition of micro-quartz on the microstructural and mechanical properties of carbon fibers and their bond performance toward cement

An electrophoretic deposition (EPD) process of micro-quartz (MQ) powder is applied to carbon fibers (CFs) with the aim to enhance their interfacial bond to cementitious matrices and to investigate its influence on the microstructural and mechanical properties of the CFs itself. The electrophoretic mobility of the MQ particles with negative charge in aqueous media was confirmed by potential sweep experiments and zeta-potential measurements. High amounts of MQ were successfully deposited onto the fiber surface, as proven by scanning electron microscopy. Single-fiber tension tests and thermogravimetric analysis showed that EPD treatment had little impact on the tensile properties and thermal stability of the modified fibers. However, storing the CFs in cement pore solution impaired temperature stability of untreated and modified fibers. X-ray diffraction and Raman spectroscopy reveal specific changes of CF's microstructure upon EPD treatment and immersion in pore solution. Single-fiber pullout tests showed that the pullout resistance of MQ-modified CFs was enhanced, relative to untreated CFs. This augmentation can be explained by an enhanced interlocking mechanisms between CF and matrix due to the deposited quartz particles on the CF surface.

Carbon Fiber Reinforced Polymer Composites with Enhanced Interfacial Properties Based on Electrostatic Assembled FGO / Oxidized CF

AbstractInterfacial properties play a critical role in the performance of carbon fiber‐reinforced composites (CFRPs). However, poor interfacial interactions between carbon fiber (CF) and polymer matrix often limit the performance improvement of CFRPs. In the present work, ethylenediamine functionalized graphene oxide (FGO) and oxidized‐carbon fiber (oxidized‐CF) are applied to prepare CFRPs through electrostatic self‐assembly. Results of Raman, TGA, SEM, and dynamic contact angle analyses confirm that FGO nanosheets are tightly bonded onto the oxidized‐CF surface. DMA results show a small increase of Tg of the oxidized‐CF‐FGO composites, as well as a great increment of energy storage modulus (E') compared to that of the untreated CF composites, which indicates an enhancement of interfacial properties. More importantly, the interfacial shear strength shows a great improvement of 30.4%, reaching 58.7 MPa. The interfacial enhancement mechanisms are further discussed based on the microstructure and performance evaluation results.

Constructing a Superior Interfacial Microstructure on Carbon Fiber for High Interfacial and Mechanical Properties of Epoxy Composites.

The interface quality is crucial for the properties of carbon fiber-reinforced polymer- matrix composites (CFRPs). In order to improve the interfacial and mechanical properties of CFRPs, a superior gradient modulus interfacial microstructure is constructed on the carbon fiber (CF) surface by chemically grafting a self-assembly carboxyl-terminated hyperbranched polymer (HP-COOH). A monofilament debonding test, a short beam shear test, an impact test and a dynamic mechanical thermal analysis (DMTA) were conducted to investigate the properties of the modified composite. Prominent improvements of 79.6% for the interfacial shear strength, 51.5% for the interlaminar shear strength, and 49.2% for the impact strength, as well as superior heat-resistance properties are achieved for composites with the gradient modulus interface over those of the untreated CF composites. The mechanism for performance improvement is mainly attributed to the enhanced CF surface energy, mechanical interlocking, and chemical bonding interactions. In particular, an atomic force microscopy (AFM) test proved that the gradient modulus interfacial microstructure formed by HP–COOH could widen the interface layer thickness and buffer the sharp variations in the modulus from CF to resin, thereby transmitting an external force and reducing the stress concentration. This work provides a facile and efficient strategy for constructing a superior and versatile interface for high- performance composites.