Interfacial Adhesion Of Carbon Research Articles

Synergistic enhancement of interfacial adhesion for CF/PEEK composites through carbene chemistry and water‐based self‐catalyzed cross‐linkable PENK‐NH2 sizing agent

AbstractTo address the issue of inadequate interfacial adhesion in carbon fiber/poly ether ether ketone (CF/PEEK) composites, an innovative approach that combines carbene chemistry and sizing treatment was meticulously designed to achieve remarkable synergistic enhancement. Specifically, cyano groups were chemical‐grafted on CF surface via carbene reaction. Meanwhile, a water‐based self‐catalyzed cross‐linkable PENK‐NH2 sizing agent with good storage stability was prepared. Noteworthy, the presence of amino groups as blocking agents of sizing agent significantly accelerated the rate of cyano‐crosslinking, thus effectively avoiding the adverse effects of excessively prolonged cross‐linking period during composites preparation. As a result, robust interaction between cyano‐modified CF and PEEK was established by cross‐linking reaction, along with chemical bonds generated between amino groups of sizing agent and ketone groups in PEEK. The maximum interlaminar shear strength (ILSS) of CF‐CN‐1.5/PEEK composites was 22.0% and 57.0% higher than CF‐1.5/PEEK and CF/PEEK composites. Furthermore, the presence of cyano‐cross‐linked structure endowed interphase with outstanding solvent‐resistance, the mechanical properties of CF composites after solvent treatment were well‐preserved. The strong synergistic interfacial interactions facilitated by chemical bonds in different components provide an effective and fascinating methodology for producing high‐performance CF/composites.Highlights Water‐based self‐catalyzed cross‐linkable PENK‐NH2 sizing agents for CF/PEEK were prepared. NH2 was introduced to avoid the adverse effects of prolonged cyano‐crosslinking. Designed carbenoid motif with cyano group was grafted on CF via carbene chemistry. The interaction between sizing agent and CF was boosted by the cyano‐crosslinking. Mechanical properties of sized composites corroded by solvent were well‐preserved.

Effect of Sizing Agents on Surface Properties of Carbon Fibers and Interfacial Adhesion of Carbon Fiber/Bismaleimide Composites.

Physicochemical, surface, and mechanical properties of three batches of T800 grade carbon fibers (CFs) treated with three kinds of sizing agents and Toray T800H CFs were characterized to study the effect of sizing agents on surface properties. Scanning electron microscopy for morphology, atomic force microscopy calculations, and results for the content of sizing agents showed that sizing agent B improved the surface roughness and CFs with high content of sizing agent always presented small surface roughness in a certain content range 1.2–1.6%. Surface energy of CFs was calculated by Young’s contact angle using the test results with water and glycol, and contact angles with LY-1 and modified-AC531 were also acquired. The results proved that CFs of sizing agent group B had the highest average surface energy and the lowest average contact angles with both LY-1 and modified-AC531. From both single-filament and tensile strength test results, the average strength of CFs of sizing agent group B was found to be the lowest, which indicated that sizing agent B had an influence on tensile strength decrease of T800 grade CFs. Comparing the results of interfacial shear strength both in a natural dry state and after hygrothermal treatment, high surface energy was found to be the key element to obtain high interfacial adhesion between T800 grade CFs and bismaleimide, and high surface roughness and low contact angle also played important roles. Among sizing agents A, B, and C, A had an effect on the interfacial shear strength decrease of CFs in the natural dry state, while C had that after hygrothermal treatment.

Improved interfacial adhesion in carbon fiber/poly (ether ether ketone) composites with the sulfonated poly (ether ether ketone) sizing treatment

AbstractA water‐soluble sulfonated poly (ether ether ketone) (SPEEK) sizing agent is prepared and applied to improve the interfacial adhesion of carbon fiber/poly (ether ether ketone) (CF/PEEK) composites. The surface morphology, surface roughness, surface chemistries, and surface free energy of SPEEK sized CF are obtained to understand the sizing effect. The results reveal the increased surface free energy and surface roughness of SPEEK sized CF. In addition, a chemical reaction between the CF surface and sizing layer is proved based on the results of XPS, IR, and 1H NMR. The interfacial structure of CF/PEEK composites is further ascertained by AFM and the appearance of gradient interface could be verified for SPEEK sized CF/PEEK composites. The formation of the gradient interface is due to the chemical reaction between the CF and sizing agent as well as the improved compatibility between the sized CF and matrix, which benefits the improvement of interfacial adhesion.

Effects of chain length of polyether amine on interfacial adhesion of carbon fiber/epoxy composite in the absence or presence of polydopamine bridging platform

To understand the complementary mechanisms between molecular interlocking and covalent interconnection that affects interfacial shear strength (IFSS), the adherence of polyether amine with varying chain length onto the surface of carbon fiber in the absence or presence of bio-derived adhesive polydopamine (PDA) as a bridge was subtly designed and studied. Without PDA, up to 25.6% and 34.7% increases in IFSS relative to untreated CF was achieved respectively for shorter and longer molecular chain of polyether amine. The longer chain length encourages molecular interlocking with epoxy molecules and produces a higher penetration depth into epoxy matrix, thus giving a larger increase in IFSS. In the presence of PDA, 39–42% IFSS increase by analogy to CF is observed due to the synergistic effects of hybrid interfacial interactions, the increasing rigidity of interphase and the improved wetting behavior. While, in this case, impact of chain length becomes less noticeable, which is mainly attributed to the trade-off between the enhanced chemical cross-linking points and the less molecular entanglement with resin.

Controlling of resin impregnation and interfacial adhesion in carbon fiber/polycarbonate composites by a spray-coating of polymer on carbon fibers

To improve the interfacial properties between carbon fibers (CFs) and polycarbonate (PC) resin, the PC resin was pre-coated onto the CF surfaces by a spray-coating method, and a post-heating process was applied for ensuring uniformity of the coating layer. To further investigate the interfacial interactions between the CFs and the coating layers, the physically-adsorbed PC resins were removed from some coated CFs by washing with solvent. The results showed that the CF/PC interfacial adhesion properties could be related to the coating thickness (or the resin impregnation) and fiber-matrix interactions. For a PC coating layer thinner than 0.15 μm, the PC could not be fully-impregnated into the CF bundles, thus leading to inferior CF/PC interfacial properties and mechanical properties in the final composites; while for a coating layer with thickness ranging from 0.15 to 0.32 μm, it allowed formation of well-impregnated interfaces; if coupled with a further hot-pressing for strengthening the interfacial bonding interactions, both the CF/PC interfacial shear strength and mechanical properties for the corresponding composites were significantly enhanced. The interfacial interactions and reinforcing mechanisms for the CF/PC composites were schematically proposed.

Nanoscale toughening of carbon fiber‐reinforced epoxy composites through different surface treatments

Interests in improving poor interfacial adhesion in carbon fiber‐reinforced polymer (CFRP) composites has always been a hotspot. In this work, four physicochemical surface treatments for enhancing fiber/matrix adhesion are conducted on carbon fibers (CFs) including acid oxidation, sizing coating, silane coupling, and graphene oxide (GO) deposition. The surface characteristics of CFs are investigated by Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, interfacial shear strength, and interlaminar shear strength. The results showed that GO deposition can remarkably promote fiber/matrix bonding due to improved surface reactivity and irregularity. In comparison, epoxy sizing and acid oxidation afford enhancement of IFSS owing to effective molecular chemical contact and interlocking forces between the fiber and the matrix. Besides, limited covalent bonds between silane coupling and epoxy matrix cannot make up for the negative effects of excessive smoothness of modified CFs, endowing them inferior mechanical properties. Based on these results, three micro‐strengthening mechanisms are proposed to broadly categorize the interphase micro‐configuration of CFRP composite, namely, “Etching” “Coating”, and “Grafting” modifications, demonstrating that proper treatments should be chosen for combining optimum interfacial properties in CFRP composites. POLYM. ENG. SCI., 59:625–632, 2019. © 2018 Society of Plastics Engineers

Improved wettability and interfacial adhesion in carbon fibre/epoxy composites via an aqueous epoxy sizing agent

In this paper, a modified epoxy emulsifier (MEE) was synthesised for preparing an aqueous epoxy sizing agent, which was used to reinforce interfacial adhesion of carbon fibre (CF)/epoxy composites. The sizing agent was evenly wrapped on the fibre surface with tiny particles, as well as increased the surface roughness of fibres; meanwhile, the activated carbon atoms on the surface of sized CF were further increased, as confirmed via SEM, AFM and XPS. The contact angle (CA) of fibres was observed via drop-on-fibre system. The results showed that the wettability of CF was significantly improved and the CA of CF was reduced by approximately 23°. According to the single-fibre fragmentation test, the interfacial shear strength of sized CF/EP composites increased by 70%–76%. The improvement of interfacial adhesion could be mainly attributed to the generation of chemical interaction bonds and the interface mechanical interlock of CF and the epoxy matrix.

Effect of hybrid sizing with nano-SiO2 on the interfacial adhesion of carbon fibers/nylon 6 composites

Polyurethane/nano-SiO2 hybrid sizing agents were deposited on the surface of carbon fibers to improve their interfacial adhesion with nylon 6. To obtain homogenous sizing agents, the nano-SiO2 surface was grafted with 3-glycidoxypropyltrimethoxy silane (GPTMS) and the most appropriate mass ratio of nano-SiO2 to coupling agent was determined by dynamic light scattering. Transmission electron micrograph (TEM) and scanning electron microscope (SEM) images of sizing agents showed modified nano-SiO2 was distributed more uniformly than the original SiO2. The effect of incorporation of nano-SiO2 in the polyurethane sizing on thermostability and hydrophobicity were studied by thermogravimetric analysis and static contact angle measurement, respectively. The chemical characteristic and morphologies of carbon fibers were researched using fourier transform infrared spectroscopy (FTIR), SEM and atomic force microscope (AFM). The results showed the roughness of the carbon fiber surface was improved when they were coated with PU/SiO2 hybrid sizing agents. Interfacial adhesion between carbon fibers and nylon 6 under dry conditions and after hygrothermal treatment was measured by transverse fibers bundle (TFB) test. For carbon fibers coated with polyurethane sizing incorporated with nano-SiO2, a remarkable increase of more than 40% and a mild increase of TFB strength were observed at dry and after hygrothermal treatment, respectively, compared with carbon fibers coated with pure polyurethane.

Improved interfacial adhesion in carbon fiber/epoxy composites through a waterborne epoxy resin sizing agent

ABSTRACTA series of self‐emulsified waterborne epoxy resin (WEP) emulsions were used as surface sizing for carbon fibers (CFs) to improve the interfacial adhesion between the CF and epoxy matrix. In this work, the hydrogenated bisphenol‐A epoxy resin (HBPAE) was modified by polyethylene glycol (PEG) with molecular weights of 400, 800, 1000, 1500, 2000, 4000, and 6000 g/mol. The properties of the WEP emulsion were examined by Fourier transform infrared spectroscopy, dynamic light scattering, and transmission electron microscopy. The surface characteristics of sized CFs were evaluated using scanning electron microscopy, atomic force microscopy, and X‐ray photoelectron spectroscopy. Afterwards, CF/EP composites were prepared and their fracture surface and interlaminar shear strength (ILSS) were examined. The results indicated that PEG2000 modified HBPAE sizing had the optimum emulsion stability and film‐forming ability. Meanwhile, the results also demonstrated that a continuous and uniform sizing layer was formed on the surface of CFs and the surface sizing was excellent in improving the chemical activity of CFs. Compared with unsized CFs, the O1s/C1s composition ratio was observed to increase from 11.51% to 33.17% and the ILSS of CF/EP composites increased from 81.2 to 89.7 MPa, exhibiting better mechanical property than that of commercial Takemoto S64 sized CFs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44757.

Optimization of plasma treatment variables for the improvement of carbon fibres/epoxy composite performance by response surface methodology

The purpose of the current work was to investigate the effect of oxygen plasma treatment of carbon fibre on the interfacial adhesion in carbon fibre/epoxy composites. The adhesion between the carbon fibre and matrix was examined by interlaminar shear strength (ILSS). It was observed that the composites prepared from plasma treated carbon fibre had higher ILSS compared with untreated fibres. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were employed to study the changes in the surface morphology of carbon fibres and the fracture of carbon fibre/epoxy composite before and after plasma treatment. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) analysis indicated that the plasma process created hydroxyl and carboxyl groups at the surface of carbon fibres. An experimental design with the identified process parameters namely, treatment time, power and flow rate of oxygen gas was followed. Experiments were performed according to the design in order to optimize the plasma variables by response surface methodology (RSM) using Box Behnken design. A second-order polynomial model was developed to predict the ILSS of carbon fibre composites in relation with the changes in plasma parameters. The process conditions were optimized with the quadratic model and the most efficient conditions were confirmed by the empirical results.

Effect of glass powder content on the mechanical and wet tribological properties of carbon fabric/phenolic composites

In order to improve the interfacial adhesion of carbon fabric/phenolic composites, the glass powders modified by silane coupling agents were introduced by repeated filtration method. Subsequently, the effects of glass powder content (0–3 wt%) on their mechanical and wet tribological properties were investigated based on the characteristics of surface micrographs, three-dimensional surface profiles, skeletal densities, and porosities. Results show that the incorporation of glass powders not only promotes the interfacial adhesion between fiber and matrix but further increases shear and flexural properties. Meanwhile, the introduction of glass powders enhances friction coefficients and improves wear resistance, whereas worsens friction stability. Notably, the carbon fabric composites containing 2 wt% glass powders exhibit the greatest shear strength, flexural modulus and strength, friction coefficient but the smallest wear rate. Optical morphology analysis demonstrates that the abrasion of counterpart stainless slider becomes gradually severe with the increase of glass powder content.

Matrix formulation and interfacial enhancement of an aeronautical carbon fabric/epoxy composites fabricated via resin transfer molding (RTM) technique

Flexural strength and interlaminar shear strength of fiber-reinforced composites are among the most concerned properties in the aeronautical sector, which are ameliorated in combination through matrix formulation and interfacial enhancement in this study. A thermosetting matrix resin consisting of diglycidyl ether of bisphenol A and diglycidyl ester of aliphatic cyclo was formulated to cater to the requirements of carbon fabric/epoxy composites fabricated by resin transfer molding (RTM) technique. The toughness and thermal stability of the formulated epoxy resin were studied in consideration of the compromise among processability, thermal and mechanical properties for potential aeronautical applications. The processability of the matrix resin suitable for RTM technique was evaluated with respect to temperature-dependent and time-dependent viscosity. A regime for the curing and post-curing cycles was established according to the differential scanning calorimeter data. Air plasma is introduced herein as a technique to enhance the interfacial adhesion of carbon fabric/epoxy composites. Composites based on the epoxy system and plasma-treated carbon fabric were fabricated using the RTM technique. The reactive groups introduced by plasma treatment are responsible for the significant improvements of mechanical properties of the resulting composites. The microscopy pictures of the fracture surfaces confirm that the failure mode of carbon fabric/epoxy composites has changed initially from primarily adhesive failure to cohesive failure.

Enhanced interfacial adhesion in carbon fiber/poly (acrylonitrile‐butadiene‐styrene) composite through fiber surface treatment by an emulsion sizing

To improve the interfacial adhesion between carbon fiber (CF) and poly(acrylonitrile‐butadiene‐styrene) (ABS) thermoplastic, an emulsion sizing whose film former was a terpolymer N‐phenylmaleimide‐styrene‐maleic anhydride (NSM)/ABS mixture was prepared. NSM, an efficient heat‐resistant modifier for ABS, could make the film former possess a superior heat resistance, which helped the sizing layer maintain integrity during the preparation of CF/ABS composite. Moreover, differential scanning calorimetry (DSC) results demonstrated that the glass transition temperature (Tg) of the NSM modified ABS achieved an improvement of 25.3°C. Particle size and distribution of the sizing agent were investigated to evaluate its stability. The FTIR spectrum obtained demonstrated that the chemical compositions of the sized CF got greatly changed and numerous functional groups appeared on sized CF. Abrasion resistance and fluffs of CF were tested and the results indicated that the sized CF obtained an appreciable enhancement in handleability. Interlaminar shear strength (ILSS) results revealed, after sizing, that the ILSS enhanced by 26.6%, due to the inserted sizing layer between CF and ABS matrix. POLYM. COMPOS., 37:2940–2949, 2016. © 2015 Society of Plastics Engineers

Surface modification of carbon fibers by a polyether sulfone emulsion sizing for increased interfacial adhesion with polyether sulfone

Interests on carbon fiber-reinforced thermoplastic composites are growing rapidly, but the challenges with poor interfacial adhesion have slowed their adoption. In this work, a polyether sulfone (PES) emulsion sizing was prepared successfully for increased interfacial adhesion of carbon fiber/PES composites. To obtain a high-quality PES emulsion sizing, the key factor, emulsifier concentration, was studied by dynamic light scattering technique. The results demonstrated that the suitable weight ratio of PES to emulsifier was 8:3, and the resulting PES emulsion sizing had an average particle diameter of 117nm and Zeta potential of −52.6mV. After sizing, the surface oxygen-containing functional groups, free energy and wettability of carbon fibers increased significantly, which were advantageous to promote molecular-level contact between carbon fiber and PES. Finally, short beam shear tests were performed to evaluate the interfacial adhesion of carbon fiber/PES composites. The results indicated that PES emulsion sizing played a critical role for the enhanced interfacial adhesion in carbon fiber/PES composites, and a 26% increase of interlaminar shear strength was achieved, because of the improved fiber surface wettability and interfacial compatibility between carbon fiber and PES.

Synergia effect of grafting polymer and coating on carbon fibers surface and interface of its composites

In this work, carbon fibers were treated with epoxy-polyurethane coating to improve the interfacial properties of carbon fiber/epoxy composites. The treatment method was divided into three phases, i.e. oxidation with oxygen plasma and coating, graft with acid anhydride and coating, plasma-grafted-sizing. The physical and chemical changes were examined using X-ray photoelectron spectroscopy, contact angle measurements, and Fourier-transform infrared spectroscopy-attenuated total reflectance technique. The tensile strength of carbon fiber and the interfacial adhesion of carbon fiber/epoxy composites were analyzed by Weibull analysis of the single fiber tensile test and by the filament fragmentation experiment of the single fiber composite. The experimental results showed that the sized carbon fiber with plasticizer had better wear-resistant properties. X-ray photoelectron spectroscopy results revealed that the plasma-grafted-sizing samples showed a significant increase in oxygen-containing groups, such as C–OH, COOH, C–O–C, and COOR. The interfacial shear strength of the plasma-grafted-sizing carbon fiber increased more significantly than the carbon fiber with sizing. This demonstrated that the surfaces of the samples were more active, hydrophilic, and rough after plasma-grafted-sizing treatments using dielectric barrier discharges operating in ambient argon mixture with oxygen.

Influence of surface properties on the interfacial adhesion in carbon fiber/epoxy composites

A polyacrylonitrile‐based carbon fiber was electrochemically oxidized in an aqueous ammonium bicarbonate solution with current density of up to 2.76 A/m2 at room temperature. X‐ray photoelectron spectroscopy revealed that the oxygen content increased with increasing current density before approaching saturation. The increase can be divided into two regions, the rapid increase region (0–1.78 A/m2) and a plateau region (1.78–2.76 A/m2). The surface chemistry analysis showed that the interlaminar shear strength (ILSS) value of the carbon fiber/epoxy composite could be improved by 24.7%. The carbon structure was examined using Raman spectroscopy in terms of order/disorder in the graphite structure and the results indicated that the relative percentage of graphite carbon in the form of sp2 hybridization increased above a current density of 1.39 A/m2. The increasing non‐polar graphite carbon on the carbon fiber surface decreased the surface energy. As a result, both the surface free energy () and its polar component () decreased when current density increased above 1.78 A/m2. The ILSS value had no direct relationship with the nature and surface density of the oxygen‐containing functional groups nor with the carbon structure. It is the surface free energy (), especially the polar component (), which played a critical role in affecting the interfacial adhesion of carbon fiber/epoxy composites. The ILSS value changed with increasing current density and could be divided into three distinct regions, as chemical interaction region (I), anchor force region (II) and matrix damage region (III). Copyright © 2013 John Wiley & Sons, Ltd.

Improved interfacial adhesion in carbon fiber/polyether sulfone composites through an organic solvent-free polyamic acid sizing

An organic solvent-free polyamic acid (PAA) nanoemulsion was obtained by direct ionization of the solid PAA in deionized water, with the average particle size of 261nm and Zeta potential of −55.1mV, and used as a carbon fiber sizing to improve the interfacial adhesion between the carbon fiber and polyether sulfone (PES). The surface characteristics of PAA coated carbon fibers were investigated using Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy and dynamic contact angle measurement. The results demonstrated that a continuous and uniform PAA sizing layer was formed on the surface of carbon fibers, and the surface energy of carbon fibers increased from 42.91 to 54.55mN/m after sizing treatment. The single fiber pull-out testing was also performed, which showed the increased interfacial shear strength (IFSS) of carbon fiber/PES composites from 33.6 to 49.7MPa by 47.9%. The major reasons for the improved interfacial adhesion were the increased van der Waals forces between the PES matrix and sizing layer as well as the chemical bonding between the sizing layer and carbon fiber surface. Furthermore, the PAA sizing also presented a positive effect on the interfacial adhesion of carbon fiber/PES composites under hydrothermal condition.

Preparation of Sizing Agents for Carbon Fiber Adapt to Various Polymer Matrix

Emulsion type sizing agent for carbon fiber was synthesized using epoxy resin (E-51) and epoxidized polybutadiene (EPB) by adding emulsifiers and other additives. Standing stabilization of sizing agents was analyzed. Meanwhile, abrasion resistance, fluffs and breakage, stiffness were used to analyze the processability of carbon fiber. The effect of sizing agents on interfacial adhesion of carbon fiber/resin composites was estimated by interlaminar shear strength (ILSS). The results showed that the sizing agent could significantly improve processability of carbon fiber due to the increase of abrasion resistance and reduce of fluffs and breakage. By adding EPB in sizing agent and adjusting the ratio to E-51, the flexibility of carbon fiber was ameliorated and the sizing agent could adapt to various resin matrices. Compared to the desized carbon fiber reinforced composite, ILSS of sized carbon fiber/epoxy resin composite was increased by 16.9%, and ILSS of sized carbon fiber/vinyl ester resin composite was enhanced by 19.1%.

Effect of Sizing Agent on the Surface of Carbon Fiber and Interfacial Adhesion of Carbon Fiber/Vinyl Ester Resin Composite

The vinyl ester resin sizing agents modified with epoxidized polybutadiene or epoxy terminated butadiene-acrylonitrile oligomer were prepared. The influence of the sizing agents on the performances of carbon fiber and its composite was studied. Surface topography of carbon fiber was characterized by scanning electron microscope (SEM). Fluffs and breakage, stiffness test were used to analyze the workability in later process of carbon fiber. The results indicated that the sizing agents had important influence to the carbon fiber and its composite. SEM images demonstrated that the sized carbon fiber had smooth surface. The sizing agent could significantly improve not only handling characteristics of carbon fiber due to the increase of fiber flexibility and reduction of fluffs and breakage, but also the interfacial adhesion of carbon fiber/vinyl ester resin composite.

Effect of Emulsion Type Sizing Agents on the Properties of Carbon Fiber and Carbon Fiber Reinforced Polymer Matrix Composite

Emulsion type sizing agents for carbon fiber were prepared by phase inversion emulsification. Standing stabilization and particle size analysis measurements were used to characterize the sizing agents. Meanwhile, the processability and surface morphology of carbon fiber were investigated. The effect of sizing agents on interfacial adhesion of carbon fiber/resin composite was estimated by interlaminar shear strength(ILSS). The results showed that the sizing agent emulsified by polyoxyethylene nonylphenol ethers phosphate ester ammonium salt (NP-10 PA) and emulsifier 602 had good stabilization. The sizing agent could significantly improve processability of carbon fiber. SEM micrographs demonstrated that the sized carbon fiber had smooth surface. By adding epoxidized polybutadiene (EPB) and adjusting the ratio to epoxy resin (E-51), the flexibility of carbon fiber was ameliorated, the ILSS of composites was increased.