Interfacial improvement of carbon fiber-reinforced methylphenylsilicone resin composites with sizing agent containing functionalized carbon nanotubes

A liquid sizing agent containing multiwall carbon nanotubes (MWCNTs) was prepared for carbon fiber (CF) reinforced methylphenylsilicone resin (MPSR) composite applications. In order to improve the dispersion of MWCNTs in the sizing agent and interfacial adhesion between CF and MPSR, MWCNTs and CF were functioned by the chemical modification with tetraethylenepentamine (TEPA) used as a MPSR curing agents. The CF before and after the sizing treatment-reinforced MPSR composites were prepared by a compression molding method. The microstructures, interfacial properties, and impact toughness of CF were systematically investigated. Experimental results revealed that a thin layer of MPSR coating containing functionalized MWCNTs (MWCNT-TEPA) was uniformly grafted onto the surface of CF. The sized CF-reinforced MPSR composite showed simultaneously remarkable enhancement in the interlaminar shear strength and impact toughness. Meanwhile, the tensile strength of CF had no obvious decrease after sizing treatment. In addition, the interfacial reinforcing and toughening mechanisms were also discussed. We believe that the facile and effective method in preparing multifunctional fibers provides a novel interface design strategy of carbon fiber composites for different applications.     

Improving mechanical and thermal properties of short carbon fiber/polyamide 6 composites through a polydopamine/nano-silica interface layer

Carbon fiber (CF) reinforced matrix composites have been applied widely, however, the interfacial adhesion of composites is weak due to smooth and chemically inert of CF surface. To solve this problem, A polydopamine/nano-silica (PDA-SiO₂) interfacial layer on carbon fiber surface was constructed via polydopamine and nano- SiO₂ (CF-PDA-SiO₂) by a facile and effective method to reinforce polyamide 6 composites (CFs/PA6). The effects of PDA-SiO₂ interfacial layer on crystallization structure and behavior, thermal properties, and mechanical properties of CFs/PA6 composites were investigated. Furthermore, interfacial reinforcement mechanism of composites has been discussed. This interfacial layer greatly increased the number of active groups of CF surface and its wettability obviously. The tensile strength of CF-PDA-SiO₂/PA6 composites increased by 28.09%, 19.37%, and 26.22% compared to untreated-CF/PA6, CF-PDA/PA6, and CF-SiO₂/PA6 composites, respectively, which might be caused by the increased interfacial adhesion between CF and PA6 matrix. The thermal stability, crystallization temperature, crystallinity, and glass transition temperature (T_g) of CF-PDA-SiO₂/PA6 composites improved correspondingly, attributing to the heterogeneous nucleation of nano-SiO₂ in the crystalline area and hydrogen bonds with molecular chains of PA6 in the amorphous area. This work provides a novel strategy for the construction of interfaces suitable for advanced CF composites with different structures.     

Interface improvement of carbon fiber/methylphenylsilicone resin composites by fiber surface coating of polyhedral oligomeric silsesquioxanes

To enhance interfacial properties of carbon fibers (CFs)-reinforced methylphenylsilicone resin (MPSR) composites, we introduced an appropriate interface reinforced by trisilanolphenyl-polyhedral oligomeric silsesquioxanes (trisilanolphenyl-POSS) between CFs and MPSR with a liquid phase deposition strategy. Chemical bonds among silanol groups of trisilanolphenyl-POSS, hydroxyl-functionalized CF (CF–OH), and silanol end groups of MPSR in the coating were expected to be formed through condensation reaction during the prepared process. CFs with and without sizing treatment-reinforced MPSR composites were prepared by a compression molding method. X-ray photoelectron spectroscopy revealed that trisilanolphenyl-POSS particles enhanced the contents of fiber surface oxygen-containing groups and silicon-containing functional groups. Scanning electron microscopy and atomic force microscopy images showed that trisilanolphenyl-POSS nanoparticles have been introduced onto the fiber surface obviously and the surface roughness increased sharply. Dynamic contact angle analysis indicated that trisilanolphenyl-POSS-modified sizing agent could improve the fiber wettability and surface energy significantly. Short-beam bending test and impact toughness test results showed that the interlaminar shear strength and impact resistance of the sized CFs composites were enhanced greatly with increasing amplitudes of more than 35 and 27% in comparison with those of untreated CF composites, respectively. Cryo-fractured surface topographies of composites confirmed that interfacial adhesion between CFs and MPSR has been improved after sizing treatment. Meanwhile, the sizing treatment does not decrease single fiber tensile strength.     

Mechanical behavior and microstructure of cement composites incorporating surface-treated multi-walled carbon nanotubes

Multi-walled carbon nanotubes after modified by using a H₂SO₄ and HNO₃ mixture solution were added to cement matrix composites. The mechanical properties of the newly formulated composites were analyzed, and the results show that the treated nanotubes can improve the flexural strength, compressive strength, and failure strain of cement matrix composites. The porosity and pore size distribution of the composites were determined by using Mercury intrusion porosimetry, and it is observed that the addition of carbon nanotubes can fine the pore size distribution and decrease porosity. The phase composition was characterized with Fourier transform infrared spectroscopy. It is found that there are interfacial interactions between carbon nanotubes and the hydrations (such as C-S-H and calcium hydroxide) of cement, which will produce a high bonding strength between the reinforcement and cement matrix. The mineralogy and microstructure were analyzed by using scanning electron microscope. It is shown that carbon nanotubes act as bridges across cracks and voids, which guarantees the load-transfer in case of tension.     

Enhanced interfacial strength and mechanical properties of carbon fiber composites by introducing functionalized silica nanoparticles into the interface

Introducing nanoparticles onto the surface of carbon fibers (CFs) is a useful method for enhancing the quality of fiber-matrix interface. In this work, a liquid sizing agent containing functionalized silica nanoparticles (SiO₂) was well prepared to improve interfacial strength and mechanical properties of composites. In order to enhance the dispersion of SiO₂ nanoparticles in sizing agent, SiO₂ nanoparticles were chemically grafted with 3-aminopropyltriethoxysilane (APS), and then silanized silica (SiO₂-APS) was introduced into the interphase by a conventional sizing process as well. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) confirmed the successful preparation of SiO₂-APS. Scanning electron microscopy (SEM) showed that a uniform distribution of SiO₂-APS on the fiber surface and the increased surface roughness. The sized fibers (CF/SiO₂-APS) exhibited a high surface free energy and good wettability based on a dynamic contact angle testing. Interfacial microstructure and mechanical properties of untreated and sized CFs composites were investigated. Simultaneous enhancements of interlaminar shear strength (ILSS) and impact toughness of CF/SiO₂-APS composites were achieved, increasing 44.79% in ILSS and 31.53% in impact toughness compared to those of untreated composites. Moreover, flexural strength and modulus of composites increased by 32.22 and 50.0% according to flexural test. In addition, the hydrothermal aging resistance of CF/SiO₂-APS composites has been improved significantly owing to the introduced Si-O-Si bonds at the interface.     

High improvement of interfacial and mechanical properties in reinforced PP composite by grafting polyethyleneimine modified carboxylic multi-walled carbon nanotubes on short carbon fiber

The properties of carbon fiber reinforced polymer composites (CFRPs) will benefit greatly from improving interfacial performance. In this study, the interfacial properties of the PEI-CNT-CF/PP composite was improved by coating polyethyleneimine (PEI) modified carboxylic multi-walled carbon nanotubes (CNTs) in aqueous solution (PEI-CNT) onto the surface of the CF (PEI-CNT-CF) to form a network structure. The network formation changed the chemical characteristics and compatibility of CF surface by introducing amine (imine) groups, and could induce transcrystallization (TC) at interface of composite. These positive factors led to a 24.6% increasement in the interfacial shear strength (IFSS) of PEI-CNT-CF/PP, and further resulted in 16.2% and 5.3% improvement in tensile and flexural strength, respectively. SEM images of the fracture surface demonstrated a significant improvement in the interfacial adhesion between PEI-CNT-CF and PP resin. These results indicated that the PEI-CNT was a great choice to strengthen the interface of CF/PP system.     

Effects of novolac resin modification on mechanical properties of carbon fiber/epoxy composites

The epoxy resin matrix of carbon fiber (CF)‐reinforced epoxy composites was modified with novolac resin (NR) to improve the matrix‐dominated mechanical properties of composites. Flexural strength, interlaminar shear strength (ILSS), and impact strength were measured with unfilled, 7 wt% NR, 13 wt% NR, and 18 wt% NR filled to epoxy to identify the effect of adding NR on the mechanical properties of composites. The results showed that both interfacial and impact properties of composites were improved except for flexural property. The largest improvement in ILSS and impact strength were obtained with 13 wt% loading of NR. ILSS and impact strength were improved by 7.3% and 38.6%, respectively, compared with the composite without NR. The fracture and surface morphologies of the composite specimens were characterized by scanning electron microscopy. Intimate bonding of the fibers and the matrix was evident with the content of 7–13 wt% NR range. Decrease of crosslinking density and formation of NR transition layer were deduced with adding NR. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

碳纳米管/碳纤维混杂多尺度增强体研究现状

碳纳米管(CNTs)优异的力学性能使其成为复合材料的理想增强材料,将CNTs引入到碳纤维(CF)表面制备CNTs/CF纳、微米复合增强体,可同时改善复合材料的界面剪切强度和冲击强度,从而获得具有优异综合性能的复合材料。本文综述了CNTs/CF混杂多尺度增强体的制备方法及其复合材料的性能。     

Sodium citrate-assisted synthesis of nano-manganese oxide on carbon fiber for enhancing the mechanical and frictional performances of carbon fiber-reinforced resin matrix composites

Aiming to enhance the carbon fiber (CF)/resin interfacial adhesion, this report describes the novel application of sodium citrate (SC) as an auxiliary reducing agent and surface regulator to control the morphology of nano-manganese dioxide (MnO₂) on the CF surface. The composites were fabricated by means of controlling the molar concentration ratio of SC to Mn source (0:1, 1:3, 1:2, and 1:1) in hydrothermal synthesis. The results reveal that MnO₂ nanosheets on the CF surface become denser as the concentration of SC is 1/3 of Mn source, which makes advance to the surface roughness and surface energy of CF. Simultaneously, the tensile strength of as-prepared composite is increased by 52.8%. The homologous friction coefficient tends to be high and stable and the wear volume is significantly reduced by 63.8 and 26.5% under the applied loads of 3 and 5 N in contrast with the original composites prepared without SC. As a result, it can be inferred that SC plays a crucial role in enhancing the interfacial bonding strength between the CF and matrix, providing insights into the interface control of CF-reinforced resin matrix composites.     

Reinforcing effect of multi-walled carbon nanotubes on microstructure and mechanical behavior of AA5052 composites assisted by in-situ TiC particles

In this research, the synergistic effects of multi-walled carbon nanotubes and in-situ synthesized titanium carbide (TiC) on the mechanical performance of aluminum hybrid composites were studied. The microstructural characterization involving the influence of both titanium carbide and carbon nanotubes was investigated. The reinforcing effects of both titanium carbide and multi-walled carbon nanotubes on the micro-hardness, tensile strength, and impact strength of the composites were also investigated. The microstructures of the fractured tensile and impact test surfaces were examined through FESEM (Field Emission Scanning Electron Microscope). Clear peaks of titanium carbide (TiC) and aluminum carbide (Al₄C₃) were observed in the X-Ray Diffraction (XRD) analysis. The micro-hardness of the aluminum composites was significantly improved after the reinforcement with CNT and TiC. The highest ultimate tensile strength and yield strength were found with Al–9%TiC-1%MWCNT and are equal to 206.44 MPa and 136.15 MPa, respectively, whereas a 16% decrease in the impact strength of Al–9%TiC-1%MWCNT was witnessed when compared to base alloy. The effects, such as CNT pull-out, CNT bridging was seen from tensile fractography of the composites. Further, the crack initiation from the pull-out cavity was also assumed to affect the fracture mechanism. Cleavage facets were associated both with the impact and tensile fracture surfaces of the composites. With the superior mechanical properties obtained, the aluminum hybrid composite can be replaced for different structural applications.     

Study on the mechanical properties and microstructure of high-performance carbon fiber/epoxy composites

A high-toughness epoxy has been prepared using carboxyl-terminated butadiene acrylonitrile (CTBN) as a toughening agent to modify the AG-80 epoxy resin. High-performance carbon fiber/epoxy (CF/EP) composites are fabricated using the CTBN-toughened epoxy resin as the matrix and two types of CF, namely, T800SC and T800HB, as reinforcement. The mechanical properties of the matrix, surface properties of the CFs, tensile properties, and fracture morphologies of the composites are systematically investigated to elucidate the key factors influencing interfacial bonding in high-performance CF/EP composites. The results reveal that the most significant improvement in toughness is achieved when the CTBN content is 6.90 wt.% in the epoxy resin. Owing to the high content of polar functional groups and excellent surface wettability of T800SC, the T800SC/EP composite exhibits superior mechanical properties compared with the T800HB/EP composite.     

Anisotropic conductivity of magnetic carbon nanotubes embedded in epoxy matrices

Maghemite (γ-Fe₂O₃)/multi-walled carbon nanotubes (MWCNTs) hybrid-materials were synthesized and their anisotropic electrical conductivities as a result of their alignment in a polymer matrix under an external magnetic field were investigated. The tethering of γ-Fe₂O₃ nanoparticles on the surface of MWCNT was achieved by a modified sol–gel reaction, where sodium dodecylbenzene sulfonate (NaDDBS) was used in order to inhibit the formation of a 3D iron oxide gel. These hybrid-materials, specifically, magnetized multi-walled carbon nanotubes (m-MWCNTs) were readily aligned parallel to the direction of a magnetic field even when using a relatively weak magnetic field. The conductivity of the epoxy composites formed in this manner increased with increasing m-MWCNT mass fraction in the polymer matrix. Furthermore, the conductivities parallel to the direction of magnetic field were higher than those in the perpendicular direction, indicating that the alignment of the m-MWCNT contributed to the enhancement of the anisotropic electrical properties of the composites in the direction of alignment.     

Multi-component nanocomposites of epoxy/silsesquioxane reinforced with carbon fibers and carbon nanotubes processed by resin transfer molding

ABSTRACT

In this work, an epoxy resin modified by silsesquioxane oligomers was used to produce multi-component nanocomposites reinforced with carbon fiber (CF) and multi-walled carbon nanotubes (CNT) by resin transfer molding (RTM). The combination of sonication process with the incorporation of silsesquioxane domains (i.e. increasing the degree of crosslinking of the epoxy matrix), improved the mechanical strength of the hybrid matrix and hybrid/CF/CNT nanocomposites. The multi-component nanocomposites produced by RTM presented Young modulus of 35 ± 8 GPa, tensile strength of 303 ± 41 MPa and impact strength of 1.0 ± 0.3 kJ m^?1. The results showed a significant increase in the tensile strength and impact resistance of the epoxy matrix by the incorporation of silsesquioxanes and sonication before curing of the matrices, showing the promising potential of this multi-component nanocomposite for pipelines and other structural applications.     

Effects of carbon nanotube functionalization on the mechanical and thermal properties of epoxy composites

Chemically functionalized multi-walled carbon nanotube (MWCNT)/bisphenol-A glycidol ether epoxy resin/2-ethyl-4-methylimidazole composites were prepared. MWCNTs were first treated by a 3:1 (v/v) mixture of concentrated H₂SO₄/HNO₃, and then triethylenetetramine (TETA) grafting was carried out. X-ray photoelectron spectroscopy analysis proved the effectiveness of H₂SO₄/HNO₃ treatment and confirmed the TETA functionalization mechanism. Chemical functionalization decreases the crystalline content of MWCNTs, however, it did not greatly disrupt their structure. Transmission electron microscopy showed that there was a TETA thin layer on the MWCNT surface, which contributes to the homogenous dispersion of MWCNTs in epoxy matrix and the improvement of the MWCNT-epoxy interfacial interaction. Thus the impact strength, bending strength and thermal conductivity of the composites are enhanced.     

Polyoxometallate-stabilized platinum catalysts on multi-walled carbon nanotubes for fuel cell applications

A novel catalyst, Pt-PMo₁₂-CNT, with well-dispersed Pt nanoparticles and monolayer PMo₁₂ on multi-walled carbon nanotubes (CNTs) is reported. A polyoxometallate (PMo₁₂) was chemically adsorbed on the surface of Pt nanoparticles and on outer walls of CNTs. These effectively prevented the agglomeration of Pt nanoparticles and CNTs due to the electrostatic repulsive interactions between negatively charged PMo₁₂ monolayers. The as-prepared Pt-PMo₁₂-CNT materials show higher electrocatalytic activity, higher cycle stability, and better tolerance to poisoning species in methanol oxidation than do Pt-CNT catalysts prepared by the same method. The reasons for the improved catalytic performance of the Pt-PMo₁₂-CNT catalysts are discussed.     

Properties of LDPE/POE-g-MA Composites Containing Multiwall Carbon Nanotubes Modified by Fumed Silicon Dioxide

Low density polyethylene (LDPE)/maleic anhydride grafted polyolefin elastomer (POE-g-MA) with multiwall carbon nanotubes (MWCNTs) wrapped by fumed silicon dioxide (SiO₂) were prepared by melt mixing. The results revealed that SiO₂ improved the dispersion of MWCNTs on matrix. SiO₂ and MWCNTs both had a heterogeneous nucleation effect on matrix and the crystallinity of composites increased with adding SiO₂, MWCNTs and MWCNTs/SiO₂. The addition of MWCNTs modified by SiO₂ increased tensile strength and elongation at break of composites compared with composite with raw MWCNTs. MWCNTs had a strong absorption effect, leading to an obvious decrease in reflectance at 1060 nm of composites.     

Improving interfacial compatibility by a micro–nano synergetic structure for high-performance epoxy composites

A multiscale functional filler of micro–nano synergetic structure was successfully prepared via in-situ growth of silica (SiO₂) on biomimetic dopamine modified carbon fiber (CF) surface. The CF-SiO₂ hybrid as a reinforcement possessed lubricating and reinforcing effect to enhance tribological performance, thermal stability and thermomechanical property of epoxy (EP) composites. The micro–nano synergetic structure was of great importance for ameliorating the compatibility and interfacial adhesion between CF and EP matrix, which was conductive to transferring stress from matrix to fiber and alleviating stress concentration. It was concluded that the friction coefficient and wear rate of EP/CF-SiO₂ were 0.382 and 1.12 × 10⁻⁵ mm³/N·m, that is, a decline of 58% and 2.5 times, respectively, compared to EP/CF. The CF-SiO₂ hybrid exhibited excellent friction-reducing and anti-wear performance.     

Distribution and stability of carbon nanotubes during multi-pass friction stir processing of carbon nanotube/aluminum composites

Multi-pass friction stir processing was used to fabricate multi-walled carbon nanotube/aluminum composites with a high volume fraction (>50%) of reinforcing material homogeneously dispersed in the matrix. The microhardness of the produced composites were two times higher than the original aluminum alloy. SEM and TEM analyses of the microstructures indicated that the reinforcing phase was uniformly distributed after three friction stir passes but the thermo-mechanical cycles destroyed the tubular structure of the carbon nanotubes. TEM micrographs revealed that carbon nanotubes were mostly transformed to polyaromatic and turbostratic carbon structures along with Al₄C₃ after 3 passes.     

Supercritical carbon dioxide-assisted silanization of multi-walled carbon nanotubes and their effect on the thermo-mechanical properties of epoxy nanocomposites

Supercritical carbon dioxide was employed as the solvent for the functionalization of multi-walled carbon nanotubes (MWCNTs) with an epoxy-capped silane. The silanization protocol was found to be a suitable green alternative to traditional routes that rely on organic solvents for grafting nearly monolayers of silane molecules onto the nanotube surfaces. The addition of silanized MWCNTs to a model epoxy markedly increased its T_g, and measurements of the network cooperativity length scale linked this change to a reduction in polymer segment mobility. Composites filled with low loading levels of both pristine and silanized MWCNTs exhibited significantly higher strain at break and toughness than the neat epoxy, and the greatest improvements were observed at low loading levels. SEM analysis of the composite fracture surfaces revealed that nanotube pullout was the primary failure mechanism in epoxy loaded with pristine MWCNTs while crack bridging predominated in composites containing silanized MWCNTs as the result of strong interfacial bonding with the matrix. The elevated T_g and toughness achieved with small additions of silanized MWCNTs promise to extend the engineering applications of the epoxy resin.     

Synthesis and characterization of multi-walled carbon nanotubes reinforced polyamide 6 via in situ polymerization

Polyamide 6 (PA6)/carbon nanotubes (PA6/CNTs) composites have been prepared by in situ polymerization of ε-caprolactam in the presence of pristine and carboxylated multi-walled carbon nanotubes (MWNT and MWNTCOOH). Viscosity measurements show that adding 0.5 wt% of carbon nanotubes (CNTs) does not affect the molecular weight of PA6. Compared with pure PA6, the yield strength of PA6/CNTs composites loaded with 0.5 wt% CNTs is almost unchanged, and the tensile strength is increased slightly. Dynamic mechanical analysis (DMA) demonstrates that both the storage modulus (E′) and glass transition temperature (T_g) of the PA6/CNTs composites increase, particularly for PA6/MWNTCOOH, indicating there is some chemical bonding between PA6 and MWNTCOOH. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and ultra small-angle X-ray scattering (USAXS) show that MWNT and MWNTCOOH are well dispersed in PA6 matrix. Comparison of the USAXS data with a stiff-rod model and wormlike rod model reveals that the CNTs are quite flexible, regardless the degree of chemical modification. Due to the flexibility of CNTs, mechanical properties of the PA6/CNTs composites are marginally enhanced.