The improvement in interfacial shear strength of wood fiber/epoxy composite by sizing with epoxy sizing agent containing MWCNTs

This paper discloses a feasible and high efficient strategy for wood fiber treatment to introducing multi‐wall carbon nanotubes (MWCNTs) to the surface of wood fibers for the aim of improving the interfacial shear strength of wood fiber/epoxy composite. Briefly, a layer of MWCNT was deposited on wood fibers through sizing wood fibers with epoxy sizing agent containing amine‐treated MWCNTs (MWCNT‐PEI). The surface functional groups, morphology, wettability, and interphase properties of MWCNTs on the surface of wood fiber were studied. The remarkable enhancements were achieved in interfacial shear strength of reinforced composites by dipping wood fiber in MWCNTCOOH suspension and wood fiber sizing containing MWCNT‐PEI.     

Effect of carbon fiber surface functionality on the moisture absorption behavior of carbon fiber/epoxy resin composites

Polyacrylonitrile (PAN)‐based carbon fibers were electrochemically oxidized in aqueous ammonium bicarbonate with increasing current density. The electrochemical treatment led to significant changes of surface physical properties and chemical structures. The oxidized fibers showed much cleaner surfaces and increased levels of oxygen functionalities. However, it was found that there was no correlation between surface roughness and the fiber/resin bond strength, i.e. mechanical interlocking did not play a major role in fiber/resin adhesion. Increases in surface chemical functionality resulted in improved fiber/resin bonding and increased interlaminar shear strength (ILSS) of carbon fiber reinforced epoxy composites. The relationship between fiber surface functionality and the hydrothermal aging behavior of carbon fiber/epoxy composites was investigated. The existence of free volume resulted from poor wetting of carbon fibers by the epoxy matrix and the interfacial chemical structure were the governing factors in the moisture absorption process of carbon fiber/epoxy composites. Copyright © 2016 John Wiley & Sons, Ltd.     

Influence of coupling agent chain lengths on interfacial performances of carbon fiber and polyarylacetylene resin composites

The influence of chain lengths on interfacial performances of carbon fiber/polyarylacetylene composites was studied. For this purpose, four coupling agents, methyltrimethoxysilane, propyltrimethoxysilane, octyltrimethoxysilane and dodecyltrimethoxysilane, were grafted onto fiber surface to obtain different chain lengths. The resulting carbon fiber surface was characterized by XPS and dynamic contact angle test. Interfacial adhesion in the resulting fiber reinforced polyarylacetylene resin composites was also evaluated by fracture morphology analysis and interfacial shear strength test. It was found that the interfacial adhesion in composites greatly increased with chain lengths on fiber surface. The improvement of interfacial adhesion was attributed to the interaction between the chain of coupling agents on fiber surface and that of polyarylacetylene resin at the interface. Copyright © 2009 John Wiley & Sons, Ltd.     

Enhancement of composite‐metal interfacial adhesion strength by dendrimer

The interface between carbon fiber reinforced polymer composites and metal plays a critical role in determining the strength of epoxy/metal laminated composites. We propose to introduce one dendrimer layer into the epoxy/metal interface, aiming to enhance the interfacial adhesion strength so that the interface could more effectively transfer the load from epoxy to metal. In this paper, the preparation and adsorption of dendrimer layer onto the alumina surface were systematically investigated. The results show that a highly stable and nanopatterned dendrimers layer was dip‐coated onto alumina substrates by adsorbing poly (amidoamine) dendrimers. It was confirmed that the dendrimers were adsorbed onto the alumina via acid‐base chemical interactions. The adsorption depends on the reaction time. The adhesion property between dendrimers and alumina was examined by sonication method. Copyright © 2010 John Wiley & Sons, Ltd.     

The interfacial feature of thermoplastic polystyrene composite filled with nitric acid oxidized carbon fiber

The quality of interfacial interaction is dictated by the surface chemistry of the carbon fibers and the composition of the matrix. The composition of polystyrene was modified by the addition of maleic anhydride (MAH) grafted polystyrene. The surface properties of the various matrix formulations were characterized by contact angle. Carbon fibers were modified by oxidation in nitric acid. The surface composition of the carbon fibers was characterized. The interaction between modified polystyrene and the carbon fibers was studied by single fiber pull‐out tests. The best adhesion behavior was achieved between polystyrene containing grafted MAH and nitric acid oxidation carbon fibers. The addition of MAH‐grafted polystyrene to the unmodified polystyrene caused the interfacial shear strength (IFSS) to increase. The IFSS of this fiber‐matrix combination allowed for the full utilization of the tensile strength of polystyrene. Copyright © 2009 John Wiley & Sons, Ltd.     

Wettability of carbon fibers modified by acrylic acid and interface properties of carbon fiber/epoxy

The oxidation-reduction and pre-irradiation induced methods were employed to study the effect of acrylic acid modification on the wetting and adsorption ability of carbon fiber (CF) in epoxy solution and the interfacial properties of CF/epoxy. Systematic experimental work was conducted to determine the surface topography, surface energy, surface chemical composition, absorbability and tensile strength of carbon fibers and interfacial adhesion of CF/epoxy before and after modification. The roughness, surface energy, amount of containing-oxygen functional groups and wetting ability were all found to increase significantly after modifications. The tensile strength of carbon fibers was improved marginally by γ-ray pre-irradiation while was decreased little by oxidation-reduction modification. Consequently, the surface modifications of carbon fibers via both oxidation-reduction and pre-irradiation led to an improvement (more than 15%) of the interlaminar shear strength of CF/epoxy composites. The mechanisms of interfacial improvement of modified CF/epoxy composites are proposed.     

Interlaminar and ductile characteristics of carbon fibers-reinforced plastics produced by nanoscaled electroless nickel plating on carbon fiber surfaces

In this work, a new method based on nanoscaled Ni-P alloy coating on carbon fiber surfaces is proposed for the improvement of interfacial properties between fibers and epoxy matrix in a composite system. Fiber surfaces and the mechanical interfacial properties of composites were characterized by atomic absorption spectrophotometer (AAS), scanning electron microscopy (SEM), X-ray photoelectron spectrometry (XPS), interlaminar shear strength (ILSS), and impact strength. Experimental results showed that the O(1s)/C(1s) ratio or Ni and P amounts had been increased as the electroless nickel plating proceeded; the ILSS had also been slightly improved. The impact properties were significantly improved in the presence of Ni-P alloy on carbon fiber surfaces, increasing the ductility of the composites. This was probably due to the effect of substituted Ni-P alloy, leading to an increase of the resistance to the deformation and the crack initiation of the epoxy system.     

Improving the interfacial property of carbon fibre/epoxy resin composites by grafting amine-capped cross-linked poly-itaconic acid

To improve the interfacial properties of carbon fibre-reinforced polymer composites, a surface treatment was used to cap cross-linked poly-itaconic acid onto carbon fibres via in-situ polymerization after itaconic acid grafting. The chemical composition of the modified carbon fiber (CF) surface was characterized by X-ray photoelectron spectral and Fourier-transform infrared spectroscopy. Scanning electron microscopy and atomic force microscopy images showed that the poly-itaconic acid protective sheath was uniformly capped onto the CF surface and that the surface roughness was obviously enhanced. Chemical bonds also played a key role in the interfacial enhancement. The results showed that the interfacial shear strength of the composites with poly-itaconic acid on the carbon fibres (72.2 MPa) was significantly increased by 89.5% compared with that of the composites with pristine CF (38.1 MPa). Moreover, the poly-itaconic acid sheath promoted a slight increase in mono-fibre tensile strength. In addition, the interfacial mechanisms were also discussed. Meanwhile, the mechanical property of the functionalized CF/epoxy resin composites was also significantly improved.     

Improved thermo-oxidative stability of three-dimensional and four-directional braided carbon fiber/epoxy hierarchical composites using graphene-reinforced gradient interface layer

In order to improve the thermo-oxidative stability of three-dimensional and four-directional braided carbon fiber/epoxy composites, we introduced a gradient interphase reinforced by graphene nanoplatelets (GN) between the carbon fiber and the matrix, with a liquid phase deposition strategy. Both the interlaminar shear strength and the flexural strength of the composites were improved after thermo-oxidative aging at 140 °C for various durations (up to 1200 h). The interfacial reinforcing mechanisms are explored by analyzing the structure of the interfacial phase, thermal conductivity, weight loss, surface topography, fiber/matrix interfacial morphology and thermomechanical properties of the composites. Results indicate that the GN-reinforced gradient interphase provides an effective shield against interface oxidation, assists in thermal stress transfer, and restricts the movement of the different phases of materials at the composite interface.     

Interfacial studies on the ozone and air‐oxidation‐modified carbon fiber reinforced PEEK composites

In this work, ozone modification method and air‐oxidationwere used for the surface treatment of polyacrylonitrile(PAN)‐based carbon fiber. The surface characteristics of carbon fibers were characterized by XPS. The interfacial properties of carbon fiber‐reinforced (polyetheretherketone) PEEK (CF/PEEK) composites were investigated by means of the single fiber pull‐out tests. As a result, it was found that IFSS (interfacial shear strength) values of the composites with ozone‐treated carbon fiber are increased by 60% compared to that without treatment. XPS results show that ozone treatment increases the amount of carboxyl groups on carbon fiber surface, thus the interfacial adhesion between carbon fiber and PEEK matrix is effectively promoted. The effect of surface treatment of carbon fibers on the tribological properties of CF/PEEKcomposites was comparativelyinvestigated. Experimental results revealed that surface treatment can effectively improve the interfacial adhesion between carbon fiber and PEEK matrix. Thus the wear resistance was significantly improved. Copyright © 2009 John Wiley & Sons, Ltd.     

Grafting of hyperbranched poly(amidoamine) onto waste tire rubber powder and its potential application as the curing agent for epoxy resin

To realize the high‐valued application of waste tire rubber (WTR), hyperbranched poly(amidoamine) (PAMAM) were synthesized from the surface of WTR powders to endow its chemical reactivity. The hyperbranched PAMAM‐grafted WTR powders containing a large amount of amine groups on their surface were obtained through “divergent procedure.” First, methyl methacrylate‐grafted WTR powders (MMA‐g‐WTR) were prepared by ozone‐induced grafting polymerization. Afterwards, Michael reaction and subsequent amidation reactions were carried out repetitively to obtain hyperbranched PAMAM chains grafted from the surface of the MMA‐g‐WTR powders. The resulting hyperbranched PAMAM‐grafted WTR powders exhibit good dispersibility in water. Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and thermogravimetric analysis demonstrate the successful grafting of hyperbranched PAMAM on WTR surface. The hyperbranched PAMAM‐grafted WTR powder could be utilize as curing agent and potential toughener for epoxy resin due to abundant amine groups and elastomeric feature of WTR. Differential scanning calorimetry shows that the hyperbranched PAMAM‐grafted WTR powders can be used as effective curing agent for epoxy resin. Copyright © 2011 John Wiley & Sons, Ltd.     

Improved interfacial properties of carbon fiber/UHMWPE composites through surface coating on carbon fiber surface

Carbon fibers were coated in an attempt to improve the interfacial properties between carbon fibers and ultra‐high molecular weight polyethylene resin matrix. Atomic force microscopy, scanning electron microscopy, and X‐ray photoelectron spectroscopy were performed to characterize the changes of carbon fiber surface. Atomic force microscopy results show that the coating of carbon fiber significantly increased the carbon fiber surface roughness. X‐ray photoelectron spectroscopy indicates that silicon containing functional groups obviously increased after modification. Interlaminar shear strength was used to characterize the interfacial properties of the composites.     

The surface modification of carbon fiber for thermoplastic HDPE composites

The interfacial adhesion strength between the fiber and the matrix greatly affects the properties of the carbon fiber (CF)–reinforced composite. The presence of surface functional groups on the fiber and changes in surface roughness were determined by X-ray photoelectron spectroscopy, scanning electron microscopy (SEM), and Raman spectroscopy. The effect of surface modification of CF on the mechanical properties and tribological properties of the composites is enhanced. The performance has been significantly improved. SEM analysis showed that modification had a positive effect on the interface between fiber and matrix. In the paper, the method of CF modification and the treatment of enhanced high-density polyethylene have simple and effective characteristics, which can be widely used and have guiding significance for industrial production.     

Interfacial strength and mechanisms of silicone resin composites reinforced with 2 different polyhedral oligomeric silsesquioxanes/carbon fiber hybrids

Grafting nanoscale reinforcement onto macrolevel carbon fiber (CF) surface is an efficient approach to improve interfacial strength and properties of composites. In the research, 2 different polyhedral oligomeric silsesquioxanes (POSS)/CF hybrids have been prepared by a facile 2‐step method. Carbon fiber was grafted with aniline groups by aryl diazonium reaction using water as the reaction medium, and then separately functionalized with glycidyllsobutyl POSS (EP0418) or glycidyl POSS (EP0409) by the chemical bonding. Characterization of fiber surface structures before and after modification confirmed the covalent bonding nature between both kinds of POSS and CF. Atomic force microscopy images showed the uniform distributions of EP0418 or EP0409 modified on the fiber surface and the similar enhanced degree of surface roughness (89.3 and 88.7 nm). Dynamic contact angle tests showed that EP0409‐grafted CF (CF‐g‐EP0409) had lower contact angles and higher surface free energy than those of EP0418‐grafted CF (CF‐g‐EP0418). Interfacial strength and hydrothermal aging resistance of composites enhanced significantly after POSS modification, especially for CF‐g‐EP0409 composites. Interfacial reinforcing mechanisms of composites reinforced with 2 different POSS/CF hybrids have also been analyzed and compared.     

Acid treatment for functionalizing polyethylene fiber surfaces for enhanced adhesion to epoxy resins

The utility of high-strength, high-modulus polyethylene fibers in fiber-reinforced composites is limited due to its poor interfacial adhesion to various polymeric matrices. One way to overcome this limitation is to introduce reactive functionalities on the fiber surface capable of covalently bonding to matrix resins. Ultra high-strength polyethylene (UHSPE) fibers were treated with chlorosulfonic acid. The surface acid groups were found to considerably improve the interfacial adhesion between polyethylene fibers and epoxy resins as shown by the microbond test. These surface functionalities were found to improve the fiber wettability, as shown by contact angle measurements using the Wilhelmy balance method. Colorimetric measurements of methylene blue absorption were used to quantify the surface concentrations of the acid groups. It was possible to functionalize the UHSPE fiber surfaces using this method to obtain fibers that formed a stronger adhesive bond with epoxy resins; this was achievable without sacrificing other fiber mechanical properties.     

Interfacial Characteristics and Fracture Toughness of Electrolytically Ni-Plated Carbon Fiber-Reinforced Phenolic Resin Matrix Composites

The electrolytic plating of metallic nickel on a carbon fiber surface has been carried out in order to improve the interfacial adhesion and the mechanical properties in carbon fiber/phenolic matrix composite systems. The surface and the mechanical interfacial properties of composites are characterized by X-ray photoelectron spectrometry (XPS), surface free energy, and the critical stress intensity factor (K(IC)). From the experimental results, it is clearly revealed that the oxygen functional groups and the metallic nickel on fibers largely affect the mechanical interfacial behavior of the composites, resulting in increased surface polarity, whereas the nitrogen functional groups have no effect. Also, a good correlation between surface oxygen functional groups and mechanical interfacial properties and between wettability and K(IC) is established and it is found that a 10 A m(-2) current density is the optimum condition for this system. Copyright 2001 Academic Press.     

Influence of surface properties of graphene oxide/carbon fiber hybrid fiber by oxidative treatments combined with electrophoretic deposition

An effective way to prepare graphene oxide/carbon fiber hybrid fiber was proposed by the treatment with hydrogen peroxide and concentrated nitric acid combined with electrophoretic deposition process. Surface functional group, surface roughness, and surface morphologies of carbon fibers were examined by Fourier transform infrared spectrometer, atomic force microscopy, and scanning electron microscopy. Results showed that a uniform and thick graphene oxide films were constructed on the surface of carbon fiber. Deposition density increased by introduction of pretreatment of the carbon fiber in the electrophoretic deposition process has been shown as a possible method. Dynamic contact angle analysis results indicated that the deposition of graphene oxide significantly improved surface free energy of carbon fiber by increasing surface area and polar groups. The introduction of graphene oxide in the carbon fiber‐reinforced epoxy composites results in a 55.6% enhancement in the interfacial shear strength and confirms the remarkable improvement in the interfacial adhesion strength of the composites, and the fracture mechanism was also analyzed. Copyright © 2016 John Wiley & Sons, Ltd.     

Improved interfacial properties of PI composites through graphene oxide and carbon nanotubes on carbon fiber surface

Carbon nanotubes (CNTs) have been identified as excellent nanoreinforcements for carbon fiber (CF)–reinforced polymers regarding a wide range of engineering applications. The outstanding properties of CNTs, such as their large surface area, high mechanical strength, and low manufacturing cost bring them to be distinguished nanoreinforcements for carbon fiber–reinforced polymers to form multifunctional and multiscale composites. Electrophoretic deposition of graphene oxide for CNTs onto the CF surface was conducted. The presence of graphene oxide–CNTs may effectively increase both the roughness and wettability of the CF surface, resulting in an improvement to the interfacial bonding strength between the CF and the polyimide (PI).     

Improving the interfacial property of carbon fiber/PI resin composite by grafting modification of carbon fiber surface

The poor interfacial adhesion between carbon fibers (CFs) and polyimide (PI) resin has seriously hampered the application of CF/PI composites. In this work, the interfacial adhesion was efficiently enhanced by grafting on the CF surface. Surface morphology and surface composition of modified carbon fibers were characterized, which indicated that acrylamide was grafted successfully on the CF surface and the surface roughness was increased slightly. After grafting, the interface shear strength of modified carbon fibers/PI composites was significantly improved by 86.96%, and the interlaminar shear strength was enhanced by 55.61% due to the covalent bonds in interphase and the toughening effect of sizing agent. Moreover, the mechanical properties of composites with different interfacial adhesion were measured, which further confirmed the effect of the grafting modification.     

Surface modification of PBO fibers with 2,2-Bis (3-amino-4-hydroxyphenyl) hexafluoropropane in supercritical carbon dioxide for enhancing interfacial strength

PBO fiber is one of the most promising reinforcements in resin matrix composite because of its excellent mechanical properties. However, the inert and smooth surfaces make it the poor interface adhesion with resin matrix, which seriously limits the application in composites. In this article, we report a method to modify the surface of PBO fibers with 2,2-Bis (3-amino-4-hydroxyphenyl) hexafluoropropane（BisAPAF）in supercritical CO₂ to enhance interfacial properties. Chemical structures, surface elemental composition and functional groups, and surface morphology were characterized by FT-IR spectrometer, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM), respectively. The mechanical properties of the samples were tested by a tensile tester. Static contact angle and microdebonding tests were used to characterize the wetting ability and interfacial shear strength (IFSS) of the fiber and epoxy resin. The results showed that the BisAPAF could be solved in scCO₂ and introduced more groups, –NH₂, –OH, and –CF₃ on the fiber surface, resulting in the mechanical properties and the wettability of PBO fiber slightly improved. Moreover, the fiber surface roughness was also increased obviously. The IFSS between the modified PBO fiber and epoxy resin increased from 8.18 MPa to 31.4 MPa when the treating pressure was 14 MPa. In general, the method to modify PBO fibers surface using BisAPAF in scCO₂ can effectively improve their interfacial properties.