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In order to evaluate the effects of sizing agents on the wettability, strength loss, and properties of final filament wound structures during filament winding of carbon fibers, three types of sizing agent based on epoxy, epoxy + polyester, and epoxy + polyurethane were used to treat carbon fibers, the surface properties of carbon fiber samples after treatment were evaluated using SEM, infrared spectroscopy, dynamic contact angle analysis, and interlaminar shear strength (ILSS) test, the strength loss caused by fiber damage during filament winding was quantitatively analyzed, and the strength properties of the filament wound structures were characterized by NOL ring test. The results showed that the sizing agent treatment only slightly improved the surface free energy and ILSS of carbon fibers, but it had obvious influence on the strength loss rate of carbon fiber bundles. Added polyester or polyurethane in epoxy-based sizing may improve its protective effect for carbon fiber, and thus decrease strength loss during winding process, result in better tensile properties of carbon fiber filament wound structures. [ABSTRACT FROM AUTHOR]

The development of new bio‐based epoxy resins and the search for new application areas have become important research directions for bio‐based epoxy resins. Using protocatechuic acid (PA) as a bio‐based raw material, brominated alkenes with different chain length were introduced into PA through substitution reaction, and then oxidized to obtain epoxy resins (PA‐EP) with different epoxy values. After that, it was introduced into epoxy resin (diglycidyl ether bisphenol A [DGEBA]) sizing agent to replace part of DGEBA to prepare new sizing agents. Sizing amount test and sizing CF surface morphology show that the introduction of PA‐EP with high‐epoxy value made it easier be adhered to carbon fiber (CF) surface during sizing process. Interfacial shear strength and interlaminar shear strength of composite made of sizing CF (20 wt% PA‐EP‐3) were 56.86% and 30.29% improvement against the bare CF, which was attributed to the increase in surface energy and epoxy groups after CF sizing. Therefore, PA‐EP with high‐epoxy value was applied as sizing agent for improving interface performance of CF for the first time, and this application was less affected by its low‐output problem compared to its application as a matrix resin in the field of composite manufacturing. [ABSTRACT FROM AUTHOR]

A simple method to prepare an emulsifier was proposed to form a stable nano size emulsion as a sizing agent to enhance the interfacial bonding strength between carbon fiber (CF) and epoxy resin. The toluene diisocyanate (TDI) grafting strategy can effectively introduce hydrophilic polyethylene glycol (PEG) and hydrophobic poly(propylene glycol) (PPG) into the side chain of the epoxy resin without consuming epoxy groups. The PPG chain segment length was controlled to improve the stability of the emulsion. An emulsion prepared with EP–PEG6000–PPG2000 (EE-P20) as the emulsifier had the highest stability, and could be placed for more than 6 months without changes in the droplet size. The wettability of CF modified by this sizing agent was obviously improved, and the interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) of CF(EE-P20) were increased by 42.33% and 17.41%, respectively. It was worth noting that the moisture absorption of CF(EE-P20) was 3.12% at 90% relative humidity. The introduction of the PPG segment not only improved the storage stability of the emulsion, but also improved the moisture resistance of CF after sizing. This simple continuous grafting method provides a new idea for adjusting the structure of the epoxy sizing agent, and the obtained emulsifier has a wide application prospect in the field of the CF sizing agent. [ABSTRACT FROM AUTHOR]

The epoxy resin was modified by hyperbranched structure of hydroxyl terminated to obtain waterborne epoxy resin for using as the carbon fiber (CF) sizing agent. By mixing method of waterborne epoxy resin and water, the waterborne epoxy sizing agent can be fabricated directly. In the sizing process, free of volatile organic solvents ensure the safety of operators and environment. Moreover, the introduction of tertiary amine group in hyperbranched structure will promote the reaction between epoxy and hydroxyl groups, and thus enhance the bonding strength between CF and epoxy resin. Results showed that the introduction of sizing agent does not sacrifice the CF single fiber tensile strength. The structure of epoxy resin retained in sizing agent is beneficial to the good wettability between CF and epoxy resin according to surface energy results. Interfacial shear strength value increases from 51.75 to 72.34 MPa, and interlaminar shear strength value increases from 80.32 to 90.34 MPa. These mechanical properties show that hyperbranched epoxy resin sizing agent with a large amount of hydroxyl groups can effectively improving the interface adhesion between CF and epoxy resin, showing a broad application prospect in composite materials field. [ABSTRACT FROM AUTHOR]

The article presents a study which evaluates the interfacial shear strength of carbon fiber (CF) and epoxy microcomposites by the microbond technique and investigates the composition of CF surface by X-ray photoelectron spectroscopy (XPS). The study analyzes the chemisorptions and alignment of adsorbed thiols. Results show that among molecular orientation and chain lengths, the chemical nature of active group was essential for the development of interfacial properties in epoxy or CF composites.

Highlights Zeolitic imidazolate framework‐8 (ZIF‐8) was used to enhance the interfacial strength of composites due to its large specific surface area, uniform pore size, and high stability. Morphology‐controllable ZIF‐8 nanocrystals were synthesized by solvent method and a layer of small‐sized and height crystalline ZIF‐8 was deposited on carbon fibers via an efficient electrophoretic deposition (EPD) way. The results showed that interlaminar shear strength (ILSS) and tensile strength (TS) of carbon fibers/epoxy composites and the TS of carbon fiber were enhanced by 43.56% and 25.48%, respectively. The strong interfacial adhesion strength between carbon fibers and epoxy was attributed to improving the wettability, ionic interaction and the mechanical interlocking effect induced by porous ZIF‐8, which led to effective energy absorption and load transfer. This highly efficient and controllable method is believed to improve the mechanical properties of carbon fiber composites for a wide range of industrial uses. ZIF‐8s in different sizes and morphology were synthesized by solvent method. MOF was deposited firstly onto carbon fibers though electrophoretic deposition. Materials Studio was used to evaluate the strong anchoring strength. ILSS of composites was enhanced by 43.56%. [ABSTRACT FROM AUTHOR]

As automotive and aviation develop fast, Carbon fiber reinforced thermoplastic polymers (CFRTP) are increasingly welcomed. However, commercial sizings for CF, mainly epoxy, lack compatibility and thermal stability for high-performance thermoplastic composites. Current thermoplastic sizings are also inert for the CF surface. Therefore, here, poly(amide-imide) (PAI) with reactive catechol pendant groups were synthesized, which got rid of commercial surfactants in water dispersion due to the hydrophilia from ionizable quaternary ammonium salt pendant groups. Storage-stable aqueous sizing of highly soluble PAI was sized on CF, followed by preparations of CF/poly(ether-imide) (PEI) and CF/poly(ether-ether-ketone) (PEEK) composites. Mechanical properties considerably increased for the improved interface in composites contributed by the bridging of PAI sizing between CF surface and PEI, PEEK matrices. On one side, covalent bondings and intermolecular interactions were created between CF surface and PAI sizing. On the other side, π-π stacking and hydrogen bonding between PAI and PEI, PEEK was discovered. Compared to commercial-sized CF(cCF)/PEI, the interlaminar shear strength (ILSS), flexural strength and impact strength of pCF/PEI increased by 56.84%, 47.24%, and 48.87% to 100.22 MPa, 820.52 MPa, and 82.32 kJ/m2, respectively. [Display omitted] • Aqueous quaternized poly(amide-imide) with reactive catechol pendant group was synthesized. • The poly(amide-imide) realized solubility and thermal stability simultaneously. • Aqueous CF sizing without surfactants was prepared by self-emulsifying of poly(amide-imide). • Covalent bonding between thermoplastic sizing and CF was realized for the first time. • Mechanical performances of CF/PEI and CF/PEEK composites were improved. [ABSTRACT FROM AUTHOR]

The incorporation of nanoparticles into epoxy resin constitutes a highly effective strategy for the development of high-performance adhesives. Biobased spherical cellulose nanocrystals (SCNCs), which exhibit renewability and high specific surface area, are constantly plagued by aggregation structures during the blending modification process for enhancing and toughening epoxy nanocomposite adhesives. Here, a universal strategy to manufacture solvent-free spherical cellulose nanocrystalline fluids (SCNCs–F) was reported by covalent grafting of flexible organic chains. As expected, SCNCs–F, showing good fluidity and dispersion stability at room temperature due to the barrier function of organic chains, was expected to address the aggregation issue of SCNCs in epoxy adhesives. In addition, we successfully prepared various SCNCs–F by changing the kind of flexible organic chains, demonstrating the feasibility of this universal strategy. As a proof of concept, the modification effect of incorporating SCNCs–F as a single component filler into epoxy adhesives was studied. The uniform dispersion of SCNCs–F and its robust interfacial interaction with the matrix qualified the epoxy adhesives with excellent adhesive strength (lap shear strength of 20.64 MPa) and decent toughness (work of debonding of 19027 N/m). This work is expected to facilitate the development of novel solvent-free nanofluids and establish a pathway for the application of biomass cellulose materials in epoxy nanocomposite adhesives. [Display omitted] • A universal solvent-free fluid conversion strategy for SCNCs was developed. • The polymer corona-canopy endowed SCNCs–F with splendid fluidity and processability. • The physical state of the SCNCs–F could be tailored by adjusting the canopy structure. • Excellent strength and toughness were achieved by improving interface interactions. [ABSTRACT FROM AUTHOR]

Considering the development of CFRPs, addressing the challenge through the simplistic industrial operational methods to achieve high strength and toughness in carbon fiber-reinforced epoxy resin (EP) composites (CFRPs) is imperative. In this work, an innovative approach introduced to improve the strength and toughness of CFRPs by application of a nano emulsion encapsulated polyhedral oligomeric silsesquioxane (POSS) sizing agent (POE sizing agent). The employment of a POE sizing agent markedly enhanced the surface energy and roughness of carbon fibers (CF) as well as the interface properties of CFRPs. Furthermore, the 10-PCF (10 wt% POE sizing CF) reinforced EP unidirectional CFRPs demonstrated superior strength and toughness. Relative to the DCF (Desizing CF) reinforced EP unidirectional CFRPs, their interlaminar shear strength, flexural strength, and unnotched impact strength increased by 24.9 %, 37.8 %, and 45.6 %, respectively, reaching 99.8 ± 2.3 MPa, 1376.8 ± 21.6 MPa, and 94.9 ± 4.6 kJ/m2. Concurrently, the 10-PCF reinforced EP composite laminates exhibited outstanding impact resistance, minimal damage area, and enhanced compressive strength after impact. Additionally, the strength, bundling, and flexibility of the sized CF were maintained, ensuring the processability of CF. The utilization of POE sizing agent for strength and toughness improvement in CFRPs offers a straightforward and industrially feasible approach. This research opens up a novel strategy for high-performance CF and CFRPs preparation. [Display omitted] • POE sizing agent has small particle size, high stability, good heat resistance, and environmental friendliness • POSS was encapsulated in nano microspheres so that they could be evenly coated on the CF surface without sedimentation. • POE sizing agent increased the surface roughness of CF, surface energy, and interfacial bonding performance. • POE sizing agent improved the strength and toughness of unidirectional CRRPs. • POE sizing agent improved the CAI of CFRPs from the perspective of interface modification. [ABSTRACT FROM AUTHOR]

• The photoswitchable MOF were anchored on CF surface via layer-by-layer method. Metal-organic frameworks (MOFs) are promising candidates for improving the interfaces of composite materials. In this work, we build MOF on a carbon fiber (CF) surface by using a layer-by-layer approach in situ. The results reveal that the MOF are constructed on the surface uniformly with a nanosheet-like structure. MOF make a significant contribution to the interfacial shear strength (IFSS) and surface energy, which were increased by 70.30% and 69.75%, respectively. The tensile strength of functionalized CF do not show an obvious decrease. After loading epoxy as guest molecular into the MOF, the functionalized CF present the ability for healing the interface and the first healing efficiency is 97.01%. In the future, the functionalized CF have the potential to apply in composites with remote-control self-healing. [ABSTRACT FROM AUTHOR]

In order to comprehend the influence of different "rigid-flexible" structures on the interface strength of carbon fiber(CF)/epoxy composites, CNTs was firstly chemically grafted on CFs surface, and then polyamide (PA) was grafted onto CF-CNTs surface through varying anionic polymerization time of caprolactam [ CF-CNTs-PA n (n = 6 h, 12 h, 24 h)]. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy indicated the successful establishment of CNTs and PA. TGA demonstrated the different grafting amounts of CF-CNTs-PA n (n = 6 h, 12 h and 24 h). SEM images revealed a compactness and uniform coverage of the CNTs/PA, with increasing polymerization time, the CF and CNTs surface was covered by a thick layer of PA. The surface energy increased and then decreased. The optimal interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) of the CF/epoxy composites with a polymerization time of 12 h (CF-CNTs-PA 12h) was 86.7 and 85.4 MPa, which was 77.6% and 45.7% higher than that of untreated CF/epoxy composite. As the polymerization time grew, the impact toughness and tensile strength of CF/epoxy composites enhanced and conductivity of CF/epoxy composite reduced. In addition, the mechanisms of reinforcement and toughening were also illuminated. This work would provide a certain theoretical basis for the preparation and applications of high-performance CF composites with different structures. [ABSTRACT FROM AUTHOR]

As an important material candidate for automotive, aviation, and aerospace, the wide application of carbon fiber-reinforced epoxy resin composites (CFRPs) was important. However, restricted by the low toughness. Herein, octaaminopropyl cage polysilsesquioxane-polyurethane prepolymer (POSS-PU) was synthesized by in-situ polymerization of PU on the POSS, and then employed as the modifier for epoxy resin (EP). Compared to pristine EP, the toughness of the 7.5 wt% POSS 0.5 -PU/EP was increased by 115.3 % without compromising the tensile strength and T g. The unnotched impact strength, interlaminar shear strength (ILSS), and flexural strength of the CFRPs prepared from the modified EP were increased by 73.5 %, 7.5 %, and 42.4 %, compared to CF/EP. Additionally, the mechanical properties of CFRPs maintained a substantial improvement under low-temperature, and the CF/7.5 wt% POSS 0.5 -PU/EP was increased by 72.9 % (impact strength) and 21.7 % (ILSS), compared to those of CF/EP. Compared to the improvement in the toughness of CFRPs at room temperature, the retention rate of toughness enhancement at low temperature was approximately 100 %. CFRPs prepared by POSS x -PU/EP offered outstanding mechanical properties and hence showed great potential for future industrial applications. [Display omitted] • POSS-PU was prepared by in-situ polymerization, and uniformly dispersed in EP by physical blending. • POSS-PU greatly improved the toughness of the EP (115.3 %) without sacrificing strength and T g. • Compared to CF/EP, ILSS and impact strength of CF/7.5 wt% POSS 0.5 -PU/EP increased by 7.5 % and 73.5 %. • CF/7.5 wt% POSS 0.5 -PU/EP possessed the most outstanding cryogenic strength and toughness. • POSS x -PU/EP has excellent processability since its low consistency coefficient. [ABSTRACT FROM AUTHOR]

Abstract Carbon fiber composite laminates were interfacially reinforced through in-situ synthesis of g-C 3 N 4 on the carbon fibers. The introduced g-C 3 N 4 greatly improved the roughness, functional groups and wettability on the carbon fiber surface and markedly enhanced the interfacial properties of composite laminates. The surface free energy of carbon fibers was increased by 67.81%. Interlaminar shear strength and interfacial shear strength of composite laminates were increased from 51.84 to 72.09 MPa and 44.62–73.41 MPa, respectively. The significantly enhanced interfacial properties enabled the mechanical performance of composite laminates to reach a superior state. Tensile strength and bending strength were increased by 19.54 and 10.51%, respectively. The total absorbed energy of impact experiment was also enhanced from 1.14 to 1.78 J. Meanwhile, dynamic mechanical properties and hydrothermal aging resistance were also ameliorated significantly. The improved interfacial properties and mechanical properties were ascribed to the increased mechanical interlocking, enhanced chemical bonding and ameliorated wettability created by g-C 3 N 4. Graphical abstract Surface morphology of carbon fibers with g-C 3 N 4 and comparison of interfacial properties of carbon fiber composite laminates. Image 1 Highlights • Carbon fiber composite laminates were interfacially strengthened through in-situ synthesized graphitic carbon nitride (g-C 3 N 4). • The surface free energy of carbon fibers was increased by 67.81%. • Interlaminar shear strength and interfacial shear strength of composite laminates were increased from 51.84 to 72.09 MPa and 44.62–73.41 MPa, respectively. [ABSTRACT FROM AUTHOR]

Abstract A self-synthesized octa(γ-chloropropyl) polyhedral oligomeric silsesquioxanes (POSS) and its evolutionary amino-terminated hyperbranched structure were introduced onto the carbon fibers (CFs) surface (CF-G n -POSS-NH 2 , n = 1, 2 and 3) by chemically and successively grafting method to improve the interfacial properties of CFs/epoxy composite. The fiber surface structures could be tuned through regulating grafting generation (n) of CF-G n -POSS-NH 2 , and the polarity and roughness of CF surface increased with the incremental dendritic generation number. Interfacial shear strength (IFSS), interlaminar shear strength (ILSS) and dynamic mechanical properties of the functionalized CFs composites improved as the grafting generation increased, which may be attributed to the varying degrees of chemical interaction, mechanical interlocking and resin wettability provided by hyperbranched G n -POSS-NH 2 interface. Moreover, the interfacial structure has been also speculated and analyzed. [ABSTRACT FROM AUTHOR]

Abstract In-situ synthesis of C 3 N 4 on the carbon fiber surface was reported for enhancing interfacial properties of carbon fiber reinforced epoxy resin composite. The formed C 3 N 4 on the carbon fiber surface can greatly increase the roughness, polar functional groups and wettability of carbon fiber surface, thereby leading to significant enhancement of interfacial properties of composites. After modification, interlaminar shear strength (ILSS) and interfacial shear strength (IFSS) of carbon fibers composites are increased from 44.3 to 60.7 MPa and from 43.1 to 75.9 MPa, respectively. Moreover, the surface free energy of carbon fibers is increased by 65.6%. The improved interfacial properties endow carbon fiber composites with better mechanical properties, leading to an increased tensile strength of composites from 1063 to 1279 MPa and total absorbed energy of impact experiment from 1.22 to 1.75 J. Meanwhile, the dynamic mechanical properties and hydrothermal aging resistance are also enhanced significantly. The storage modulus increases from 64.3 to 74.1 GPa. The markedly enhancement of interfacial mechanical properties and mechanical properties could be attributed to the improved resin wettability, enhanced mechanical interlocking and increased chemical bonding induced by the existence of C 3 N 4 on the carbon fiber surface. [ABSTRACT FROM AUTHOR]

Dual-activity silicone resins (DASR) with double bonds and epoxy groups were prepared via the hydrolysis and condensation of γ-glycidoxypropyltrimethoxysilane (γ-GPS) and γ-methacryloxypropyltrimethoxysilane (γ-MPS). The hydrolysis and condensation degree was monitored during the preparation process of DASR. The epoxy groups of DASR were directly reacted with amine groups on the fiber surface attempting to improve the interfacial properties of carbon fiber (CF) composites. The CF/DASR composites represented 36.91% and 20.85% enhancement in interfacial shear strength (IFSS), compared to those of MASR composites reinforced with untreated CF and amine modified CF. In addition, the tensile strength of CF/DASR remained stable after the UV irradiation. Thus, these attractive results demonstrate that the designed dual-activity silicone resin/carbon fiber composites provide a promising approach for preparing high-performance carbon fibers composites. [ABSTRACT FROM AUTHOR]

It is a challenge to bond ceramics for engineering applications at ultrahigh temperatures in air. In this paper, a high temperature organic adhesive (HTOA) was prepared using methylphenylsilicone resins (MPSR) as the matrix, trisilanolisobutyl-methylsilicone resin/polyhedral oligomeric silsesquioxane (POSS) as the modifier, ZrB 2 , SiO 2 and Si powders as the inorganic fillers, and γ-aminopropyltriethoxysilane (KH550) as the curing agent. The synthesized HTOA was used to bond ZrB 2 -SiC-G ceramic (ZSG). The ceramic yield of MPSR was increased from 71% to 91% after being modified by trisilanolisobutyl-POSS. The average shear strength of ZSG joints bonded by HTOA was 13.2 MPa at room temperature. After 1500 °C/1 h processing, the bonding strength between HTOA and ZSG ceramic was 53.8 MPa. The inter-diffusion of elements between the HTOA and the ZSG occurred at 1500 °C and ZrSiO 4 compound was formed via the interface reaction. The excellent high-temperature performance of the prepared HTOA makes it one of the convenient and effective organic adhesive for joining ZSG for engineering applications at ultrahigh temperatures in air. [ABSTRACT FROM AUTHOR]

A novel two-layer reinforced carbon fiber (CF), i.e., Ag nanoparticles (Ag NPs)/graphene oxide (GO) reinforced CF (named as CF/Ag/GO) was prepared by an electrochemical deposition and electrophoretic deposition (EPD) consequently. The modified fiber showed an increased interfacial shear strength (IFSS) and tensile strength. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectra (FTIR), X-ray photoelectron spectroscopy (XPS), Raman spectrometer, atomic force microscopic (AFM) and dynamic contact angle analysis (DCA) were carried out to investigate CF reinforced composites. And test results demonstrated that the presence of Ag NPs and GO sheets increased the surface roughness and surface energy of CFs significantly. IFSS of CF/epoxy and the tensile strength of CFs were increased by 86.1% and 36.8%, respectively. Ag NPs filled in the cracks in CF effectively to enhance the tensile strength, while GO sheets improved the wettability of resin on CFs and formed mechanical interlocking between CFs and epoxy resin. These Ag NPs and GO sheets worked together in a ferocious synergy on the interface of CF and epoxy to cause the enhanced mechanical properties. [ABSTRACT FROM AUTHOR]

The interfacial properties between carbon fiber (CF) and matrix play a key role in the mechanical properties of carbon fiber composites. To improve the mechanical properties of fibers/epoxy composites without sacrificing tensile strength of base fibers, carbon black (CB) was introduced onto the surface of CFs by chemical vapour deposition (CVD). The distribution of CBs on the fiber surface and the change of the surface roughness were analyzed, using scanning electron microscopy (SEM) and atomic force microscope (AFM). Raman spectroscopy indicated that the defects of CF surface were repaired by CB. The wettability and surface energy of modified CFs increased obviously in comparison with those of the untreated CFs. Meanwhile, a significant increase of interlaminar shear strength (ILSS), interface shear strength tests (IFSS) and impact property were achieved in the 5-min-modified CFs, which was 22.0, 44.4 and 22.7%, respectively. In addition, the tensile strength (TS) of modified CFs showed a slight increase compared with that of untreated CFs. [ABSTRACT FROM AUTHOR]

Modified methylsilicone resin (12EO 15 -MA-SiO 2 /MSR) containing nano-silica grafted hyperbranched polymer (12EO 15 -MA-SiO 2 ) was grafted successfully onto carbon fibers (CFs) surface to enhance the interfacial properties of carbon fiber/methylsilicone resin composites. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) confirmed the chemical bonding nature between 12EO 15 -MA-SiO 2 /MSR and CFs. Scanning electron microscopy (SEM) and interfacial shear strength (IFSS) indicated that the surface morphology and interfacial properties of carbon fibers were highly dependent on the concentration of 12EO 15 -MA-SiO 2 and 12EO 15 -MA-SiO 2 /MSR. The results showed that the optimal condition was that the concentration of 12EO 15 -MA-SiO 2 /MSR was 1%, in which containing 6%-12EO 15 -MA-SiO 2 . Furthermore, significant enhancement of interfacial shear strength was achieved in the composites after modified methylsilicone resin introduced on the fiber. The tensile strength of the carbon fibers remained stable after the grafted treatment. Thus, it is a facile and effective interface design strategy to develop multifunctional fibers with desirable properties in industry applications. [ABSTRACT FROM AUTHOR]

It was a major challenge to acquire CFRPs with both great toughness and strength. Inspired by spider silk, a biomaterial with impressive toughness, we discovered that introducing highly dense weak hydrogen bonds at the interface can be applied to CFRPs toughening. Highly dense weak hydrogen bonds between the branched polyethyleneimine (PEI) and metal-organic frameworks UIO-66 at the interface of CFRPs were formed by the "bridge" of hydroxyl-rich poly (vinyl alcohol) (PVA). The break of those hydrogen bonds could dissipate substantial energy and disperse the stress, the impact toughness of CFRPs with the "PEI-PVA-UIO-66" interlayer was up to 99.53 kJ/m2. Compared with composites reinforced by CFs modified with UIO-66 by chemically grafting or by physically absorbing without PVA, the impact toughness of CF-PVA-MOF/EP improved by 45% and 33%, respectively. This means that the highly dense weak hydrogen bonds have superiority for CFRPs toughening. Meanwhile, the interfacial shear strength (100.85 MPa) and interlaminar shear strength (102.44 MPa) of CFRPs were realized by the innovative designed interfacial structure. [Display omitted] • The interphase of polyvinyl alcohol, polyethyleneimine and UIO-66 with rich hydrogen bonds was designed on CFs. • The presence of highly dense weak hydrogen bonds at the interface has superiority in toughening CFRPs. • The impact toughness and interface performance of CFRPs were improved simultaneously with no loss of fiber tensile strength. [ABSTRACT FROM AUTHOR]

Using molten urea as the solvent, carbon fibers were functionalized with carboxylic acid groups via aryl diazonium reaction in 15 min to improve their interfacial bonding with epoxy resin. The surface functionalization was quantified by X-ray photoelectron spectroscopy, which showed that the relative surface coverage of carboxylic acid groups increased from an initial percentage of 3.17–10.41%. Mechanical property test results indicated that the aryl diazonium reaction in this paper could improve the interfacial shear strength by 66%. Meanwhile, the technique did not adopt any pre-oxidation step to produce functional groups prior to grafting and was shown to maintain the tensile strength of the fibers. This methodology provided a rapid, facile and economically viable route to produce covalently functionalized carbon fibers in large quantities with an eco-friendly method. [ABSTRACT FROM AUTHOR]

Highlights: [•] A new chemical grafting method for carbon fibers was proposed. [•] The oxidation system adopts K2S2O8 and AgNO3. [•] The interfacial shear strength (IFSS) of carbon fiber increased by 61%, and the interfacial adhesion increased with dendritic generation number. [•] The tensile strength of carbon fiber does not decrease distinctly. [•] The treatment conditions are mild and convenient. [ABSTRACT FROM AUTHOR]

Abstract: Conventional electroless nickel plating was utilized to enhance the interfacial properties of PBO fibers. Moreover, the possible interfacial shear strength (IFSS) enhancing reasons were investigated. The elemental composition, crystal structure and cross-sectional morphology of nickel-plated PBO fiber were characterized by energy dispersive spectrometer (EDS), X-ray diffractometer (XRD) and transmission electron microscopy (TEM), respectively. Ultrasonic exposure tests implied that the nickel coating exhibited high adhesive durability. Scanning electron microscopy (SEM) was employed to characterize the surface morphology of PBO fibers and the de-bonding surface morphology of PBO fiber composites. Atomic force microscopy (AFM) results showed that the surface morphology of nickel-plated PBO fiber was undulating, and its surface roughness (Ra) increased obviously. Single fiber pull-out tests showed that the IFSS increased from 40.4 to 56MPa. Meanwhile, the nickel-plated PBO fiber maintained satisfactory tensile strength. Hygrothermal aging tests revealed that the nickel-plated PBO fiber had excellent hygrothermal aging resistance properties. Heat treatment results showed that IFSS was decreased with the increase of temperature. [Copyright &y& Elsevier]

Abstract: In order to improve the interfacial properties between carbon fibers and epoxy matrix, supercritical water and hydrogen peroxide were used as oxidation medium for the oxidation treatment for carbon fibers. Analysis results of X-ray photoelectron spectroscopy suggest that the oxygen content on the carbon fibers’ surfaces increases by these oxidation treatments. Scanning electron microscope and atomic force microscopy images indicate that the surface appearance of oxidized carbon fibers obviously changed. The maximal interlaminar shear strength and interface shear strength of carbon fiber/epoxy resin composite in which the fibers were treated by the supercritical water and hydrogen peroxide systems reaches 70.46MPa and 106.66MPa, increases by 13.4% and 29.6% respectively compared with untreated carbon fibers. [Copyright &y& Elsevier]

Carbon Fiber-Reinforced Polymers (CFRPs) with higher strength and toughness are indispensable to meet the demand from the rapid advancing industry sectors such as automotive, aviation, and aerospace. A novel "soft-rigid" interface layer was designed via a mild and facile self-assembly strategy to achieve simultaneous improvement for strength and toughness. The positively charged polyethyleneimine (PEI), and negatively charged nano-complex composed of metal-organic framework (UIO-66) and graphene oxide (GO) were assembled on carbon fibers (CFs) through electrostatic interaction. The results shown that the roughness and wettability on the fiber surface were significantly improved by fiber surface modifications. Compared with the composite using pristine CFs as reinforcement, the interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) of the composite with the "soft-rigid" interface phase were improved by 42.12% and 23.07%, respectively. Besides, the debonding and fracture surface of CFRPs after treatment showed improved interface performance. Moreover, the impact toughness of the composite was improved from 60.24 kJ/m2 to 89.38 kJ/m2. [Display omitted] • A novel "soft-rigid" interface layer was constructed via electrostatic assembly. • The interfacial strength and toughness of composites were improved simultaneously. • The nano-coupling interaction that essential for interface performance was proposed. [ABSTRACT FROM AUTHOR]

A simple and efficient technique was proposed to yield hyperbranched polyimidazole (HBM) on carbon fiber (CF) surface using isophorone diisocyanate (IPDI) and imidazole (MZ) as monomers. The introduced HBM dendrimers dramatically ameliorated the polar groups, roughness and wettability on the fiber surface. The mechanical performances (interfacial shear, interlaminar shear and impact strength) of CF-HBM/epoxy composite were significantly improved by 78.7%, 41.1% and 43.4% compared with untreated CF composites, respectively. Furthermore, this in-situ polymerization process on CF surface could be conducive to improve the single fiber tensile strength, the interface failure behavior and reinforcing mechanism were also explored. This work furnishes a simple and efficient strategy to construct an interface layer with strong chemical interaction and high physical entanglement through in-situ synthesis, which would provide enormous potential in preparing high-performing structural composites. Image 1 • Hyperbranched polyimidazole containing terminal imidazole groups was covalently grafted on CF surface for the first time. • HBM was self-synthesized by a facile in-situ condensation polycondensation. • HBM has the advantages of easy synthesis, high curing activity and good solubility in solvents. • HBM on interface region exhibited an excellent reinforcing efficiency (improving 78.7% in IFSS). [ABSTRACT FROM AUTHOR]

To improve the dispersion of graphene oxide (GO) nanosheets in sizing agent and to enhance the interfacial adhesion between GO and epoxy, GO nanosheets were chemically modified with cyanuric chloride (TCT) and diethylenetriamine (DETA). The functionalized GO (i.e. GO-TCT-DETA) with different contents was introduced into the carbon fiber (CF) interface by sizing process. The uniform distribution of GO sheets on CF surface and the enhancement of surface roughness were obtained. Moreover, significant enhancements (i.e., 104.2%, 100.2%, and 78.3%) of interfacial shear strength (IFSS), interlaminar shear strength (ILSS), and flexural properties were achieved in the composites with only 1.0 wt% GO-TCT-DETA sheets introduced in the fiber sizing. The GO-TCT-DETA in the interface region enhanced the stress being transferred effectively and the local stress concentrations being relieved. This study indicates that the utilization of functionalized GO is one of the alternative approaches for controlling the fiber-matrix interface and improving the mechanical properties of CF epoxy composites. Image 1 • Graphene oxide was chemically functionalized. • Functionalized GO was used for making unique epoxy-based sizing. • The treated GO sizing enhanced the interfacial properties with the epoxy matrix. • The interfacial shear strength, interlaminar shear strength, and flexural properties were all enhanced. [ABSTRACT FROM AUTHOR]

The interfacial interaction between carbon fibers (CFs) and resin matrix is an important factor affecting mechanical performances of CF-based composites. In this work, a new approach combining electrodeposition method (EDM) and "Ag–S″ bonds was applied to fabricate functional CF-based composites while preserving the mechanical properties of CFs. Silver nanoparticles were first attached on the CF surface by EDM. Then 4-aminothiophenol or 4-mercaptobenzoic acid was linked to Ag surface by Ag–S bonds to incorporate different functional groups onto the fiber surface. The interfacial shear strength was improved pronouncedly while the tensile strength was maintained consistent. The interfacial shear strength of the CFs after functionalized was increased 21.10% and 32.04%, respectively. However, the tensile strength of them decreased no more than 3%. With improved properties, these nanocomposites have potential applications for aerospace, transportation, electronics and other fields. [ABSTRACT FROM AUTHOR]