Experimental evaluation of the interfacial properties of carbon nanotube coated carbon fiber reinforced hybrid composites

A floating catalyst chemical vapor deposition (CVD) unit was utilized to grow CNT onto the surface of carbon fiber (CF). The surface morphology of the resultant fibers, CNT population density and alignment pattern were found to be depended on the CNT growth temperature, growth time, and atmospheric conditions within the CVD chamber. In contrast to the neat‐CF reinforced composites, improved interfacial shear strength (IFSS) between CF and matrix were obtained when the surface of CF was coated by CNT. Particularly, CF treatment condition for CNT‐coating with 700°C reaction temperature and 30 min reaction time has shown a considerable increase in IFSS approximately of 45% over that of the untreated fiber from which it was processed. The proper justification of fiber–matrix adhesion featured by composite interfacial properties was explained through IFSS. POLYM. COMPOS., 36:1941–1950, 2015. © 2014 Society of Plastics Engineers     

Formation of a carbon fiber/polyhedral oligomeric silsesquioxane/carbon nanotube hybrid reinforcement and its effect on the interfacial properties of carbon fiber/epoxy composites

A carbon fiber/polyhedral oligomeric silsesquioxane/carbon nanotube (CF–POSS–CNT) hybrid reinforcement was prepared by grafting CNTs onto the carbon fiber surface using octaglycidyldimethylsilyl POSS as the linkage in an attempt to improve the interfacial properties between carbon fibers and an epoxy matrix. X-ray photoelectron spectroscopy, scanning electron microscopy, dynamic contact angle analysis and single fiber tensile testing were performed to characterize the hybrid reinforcements. Interlaminar shear strength (ILSS), impact toughness, dynamic mechanical analysis and force modulation atomic force microscopy were carried out to investigate the interfacial properties of the composites. Experimental results show that POSS and CNTs are grafted uniformly on the fiber surface and significantly increase the fiber surface roughness. The polar functional groups and surface energy of carbon fibers are obviously increased after the modification. Single fiber tensile testing results demonstrate that the functionalization does not lead to any discernable decrease in the fiber tensile strength. Mechanical property test results indicate the ILSS and impact toughness are enhanced. The storage modulus and service temperature increase by 11 GPa and 17 °C, respectively. POSS and CNTs effectively enhance the interfacial adhesion of the composites by improving resin wettability, increasing chemical bonding and mechanical interlocking.     

The hierarchical structure and properties of multifunctional carbon nanotube fibre composites

The axial mechanical, electrical and thermal properties of carbon nanotubes (CNTs) can be exploited macroscopically by assembling them parallel to each other into a fibre during their synthesis by chemical vapour deposition. Multifunctional composites with high volume fraction of CNT fibres are then made by direct polymer infiltration of an array of aligned fibres. The fibres have a very high surface area, causing the polymer to infiltrate them and resulting in a hierarchical composite structure. The electrical and thermal conductivities of CNT/epoxy composites are shown to be superior to those of equivalent specimens with T300 carbon fibre (CF) which is widely used in industry. From measurements of longitudinal coefficient of thermal expansion (CTE) of the composites we show that the CTE of CNT fibres is approximately ?1.6 × 10^?6 K^?1, similar to in-plane graphite. The combination of electrical, thermal and mechanical properties of CNT fibre composites demonstrates their potential for multifunctionality.     

Effects of fiber surface grafting by functionalized carbon nanotubes on the interfacial durability during cryogenic testing and conditioning of CFRP composites

Carbon fiber reinforced epoxy (CE) composite is ideal for a cryogenic fuel storage tank in space applications due to its unmatched specific strength and modulus. In this article, inter-laminar shear strength (ILSS) of carbon fiber/epoxy (CE) composite is shown to be considerably improved by engineering the interface with carboxyl functionalized multi-walled carbon nanotube (FCNT) using electrophoretic deposition technique. FCNT deposited fibers from different bath concentrations (0.3, 0.5, and 1.0 g/L) were used to fabricate the laminates, which were then tested at room (30°C) and in-situ liquid nitrogen (LN) (−196°C) temperature as well as conditioning for different time durations (0.25, 0.5, 1, 6, and 12 h) followed by immediate RT testing to study the applicability of these engineered materials at the cryogenic environment. A maximum increment in ILSS was noticed at bath concentration of 0.5 g/L, which was ~21% and ~ 17% higher than neat composite at 30°C and − 196°C, respectively. Short-term LN conditioning was found to be detrimental due to developed cryogenic shock, which was further found to be compensated by cryogenic interfacial clamping upon long-term exposure.     

Effect of polyurethane sizing on carbon fibers surface and interfacial adhesion of fiber/polyamide 6 composites

Commercial epoxy sized carbon fibers (CFs) or unsized CFs have poor interfacial adhesion with polyamide 6 (PA6). Here, CFs are coated with polyurethane (PU) and their surface properties in terms of surface chemistry, contact angle, roughness, and morphology, are investigated. The results of Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy demonstrate PU sizing evidently increases the quantity of polar functional groups on the CFs surface. The surface energy of the PU sized fiber is calculated according to the Owens–Wendt method. Compared with unsized fibers, the contact angle of PU sized fibers is decreased while their total surface energy is increased, indicating superior wettability. Moreover, transverse fiber bundle tests are performed to determine the interfacial adhesion between the CFs and PA6 matrix. The transverse fiber bundle strength of unsized CF is measured to be 12.57 MPa. For PU sized CFs processed with sizing concentration of 1.2%, this value is increased to 24.35 MPa, showing an increase of more than 90%. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46111.     

Fabrication and electromagnetic interference shielding effectiveness of carbon nanotube reinforced carbon fiber/pyrolytic carbon composites

Carbon nanotube reinforced carbon fiber/pyrolytic carbon composites were fabricated by precursor infiltration and pyrolysis method and their electromagnetic interference shielding effectiveness (EMI SE) was investigated over the frequency range of 8.2–12.4 GHz (X-band). Carbon nanotubes (CNTs) were in situ formed through catalyzing hydrocarbon gases evaporating out of phenolic resin with nano-scaled Ni particles. The content of CNTs increased with the increase of Ni loadings (0.00, 0.50, 0.75 and 1.25 wt.%) in phenolic resin. Thermal gravimetrical analysis results showed that the carbon yield of phenolic resin increased with the addition of Ni catalyst. With the formation of CNTs, the EMI SE increased from 28.3 to 75.2 dB in X-band. The composite containing 5.0 wt.% CNTs showed an SE higher than 70 dB in the whole X-band.     

The effect of nanotube alignment on stress graphitization of carbon/carbon nanotube composites

Carbon nanotubes, when used as filler in a glass-like carbon matrix, has been reported to induce stress graphitization in the matrix. The effects on stress graphitization of the amount of carbon nanotube loading and nanotube orientation in the composite were investigated through microscopy and X-ray diffraction analyses. Results showed that an increase in nanotube content and nanotube alignment could increase the extent of formation of anisotropic regions, thereby hastening stress graphitization. It was shown that the distance between nanotubes could affect the formation of the anisotropic structures, such that they could develop in a circumferential manner around the nanotubes when the nanotubes are situated far from each other or develop continuous regions between nanotubes when they are closer together. The development of these microstructures and its relationship to the residual stresses that accumulate in the material during heat treatment is discussed here.     

Influence of surface modification of carbon nanotube on microstructures and properties of polyamide 66/multiwalled carbon nanotube composites

The melt‐mixing polyamide 66 (PA66) composite samples that incorporated pure, acid‐ and amine‐functionalized multiwalled carbon nanotubes (MWCNTs) were prepared in order to enhance mechanical and frictional properties of PA66 composites. The homogeneous dispersion of amine‐functionalized MWCNTs (D‐MWCNTs) in PA66 matrix was observed from the significantly uniform morphology of tensile fractured surface of the composites. Differential scanning calorimetry measurement indicates that D‐MWCNTs acted as effective nucleation agent for PA66 matrix and the crystallinity of PA66 was increased. The fracture stress and tensile modulus of the composites were significantly improved with the incorporation of D‐MWCNTs, owing to the good dispersion of D‐MWCNTs. Compared with PA66, the PA66 composites with 1.0 wt% D‐MWCNTs were improved considerably in both wear and friction properties owing to the change of the tribological mechanisms. The good dispersion of D‐MWCNTs in PA66 and good interface compatibility between D‐MWCNTs and PA66 favored the formation of a thin layer on the contact surfaces during wear and friction test, which played an important role in reducing wear and friction of the composite and in suppressing the transverse cracks. These results prove the importance of D‐MWCNTs in a positive change of the mechanical and frictional properties of PA66 composites and suggest the applicability prospect of PA66/D‐MWCNTs composites in engineering components.POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Nanotube surface functionalization effects in blended multiwalled carbon nanotube/PVDF composites

A mixed fill system of multiwalled carbon nanotubes (MWCNT) and hydroxylated MWCNT (HO‐MWCNT) in a poly(vinylidene fluoride) (PVDF) matrix was investigated to improve nanotube dispersion and enhance electrical percolation for the bulk nanocomposites. Nonfunctionalized MWCNT were blended at various concentrations into dimethylformamide solutions containing PVDF with 0, 5, or 10 wt % HO‐MWCNT. Composite samples prepared from these solutions were examined by four‐point probe resistivity measurements. The percolation threshold decreased from 0.49 wt % MWCNT in binary MWCNT/PVDF composites to 0.25 wt % for ternary composites containing MWCNT/HO‐MWCNT/PVDF, with either 5 or 10 wt % HO‐MWCNT. In the case of the ternary composite with 10 wt % HO‐MWCNT, the lowest fill percent of MWCNT (0.25 wt %) measured a conductivity that was three orders of magnitude higher than the binary MWCNT/PVDF composite containing twice the concentration of MWCNT (0.5 wt %). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Anisotropic interfacial friction of inclined multiwall carbon nanotube array surface

Anisotropic interfacial friction of an inclined, multiwalled carbon nanotube (MWCNT) array surface fabricated on a commercial electrostatic adsorption film substrate has been experimentally studied. As a typical case, the friction force of steel ball/inclined MWCNT along the inclined direction is 40% larger than that against the inclined direction. The significant interfacial friction anisotropy remains stable even after nearly 4000 sliding cycles. While the tilt of MWCNT close to the top surface layer significantly affected the interfacial friction, the underlying nanotubes only has limited effects. Based on the van der Waals interaction between the MWCNT and the steel ball, the achieved anisotropic interfacial friction at different sliding directions is quantitatively modeled and explained. The interplay between the lateral friction and normal adhesion force has also been found during the unloading process of friction test.     

Effect of carbon nanotube length and density on the properties of carbon nanotube-coated carbon fiber/polyester composites

Carbon nanotubes (CNTs) have been synthesized on the surface of carbon fiber/fabric using catalytic chemical vapor deposition (CVD) at a temperature of 550 °C. A coating of Ni catalyst on the fiber surface is applied using the electroless dip coating method. The dependence of the length and quantity of CNTs on the growth time is studied by varying the run time of the CVD reactor from 5 to 25 min. Scanning electron microscopy shows good coverage of the carbon fiber surface by the CNTs. It is observed that both the length and density of CNTs are functions of the growth time. Up to a critical growth time, both the storage modulus and the interfacial shear stress of CNT-coated carbon fiber/polyester composites are seen to increase substantially.     

碳纳米管／橡胶复合材料研究进展

介绍了碳纳米管(CNT)/橡胶复合材料的制备方法,综述了CNT对橡胶复合材料硫化行为、物理机械性能及电性能的影响.指出CNT在橡胶中分散不均、与橡胶界面结合不佳是CNT/橡胶复合材料拉伸强度提高不显著的主要原因.今后该领域的研究方向应是通过采用新的制备方法或改进现有方法促使CNT在橡胶基质中均匀分散,以提高橡胶复合材料的拉伸强度.     

The effect of surface functionalization of carbon nanotubes on properties of natural rubber/carbon nanotube composites

The objective of this study was to prepare natural rubber composites filled with carbon nanotubes (CNTs) that show an electrical percolation threshold at very low CNT concentrations. Therefore, two methods of surface functionalization of CNTs were investigated to enable an improved dispersion of CNTs and chemical interaction between CNTs and rubber matrix. On one hand, the CNTs have been functionalized ex situ by acid treatment and silanization reaction with bis(triethoxysilylpropyl) tetrasulfide before mixing with the rubber and otherwise in situ functionalization was directly carried out during the processing of the composites in the internal mixer. The grafting of silane molecules onto CNT surface was established by Fourier transform infrared spectroscopy and scanning electron microscopy. Tensile tests revealed the outstanding properties of composites prepared by in situ silanization method. The in situ silanization led to a better dispersion of the CNTs and the formation of chemical linkages between CNT surface and rubber and this became manifest in higher reinforcement of the rubber, higher crosslink densities, and a lower electrical percolation threshold. It was also shown that the in situ silanization is retarding the vulcanization reaction. POLYM. COMPOS., 36:2113–2122, 2015. © 2014 Society of Plastics Engineer     

Preparation of a carbon nanotube/carbon fiber multi-scale reinforcement by grafting multi-walled carbon nanotubes onto the fibers

To prepare a carbon nanotube (CNT)/carbon fiber multi-scale reinforcement (MSR), multi-walled carbon nanotubes (MWCNTs) functionalized at the end caps with hexamethylene diamine (HMD) are grafted onto the surfaces of carbon fibers treated with acyl chloride. The surface element concentrations, surface functional groups and morphology of the MSR were examined by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XPS spectra indicate that sp² and sp³ carbon atoms are major components in the MSR surface, and the carbon fiber surface structure is not destroyed. There is 17.41% of C-NH_x in the surface of the MSR, which suggests that MWCNTs are covalently grafted onto carbon fiber surfaces. SEM shows that the grafted MWCNTs stick to the carbon fiber surface at different angles, and are uniformly distributed along the outer edges of the grooves in the fiber surface. The grafted MWCNTs are 50-200 nm in length and around 14 nm in diameter. It was found that the grafting increases the weight of carbon fiber by 1.2%, which implied that a considerable amount of MWCNTs were grafted onto carbon fiber surfaces.     

Direct measurement of grafting strength between an individual carbon nanotube and a carbon fiber

Hierarchical structures consisting of carbon nanotubes (CNTs) grafted onto a carbon fiber (CF) have the potential to improve the performance of fiber/polymer composites. The strength between a CNT and a CF is a key factor that influences the load-transfer behavior and inter-laminar properties. Here, we directly measured the grafting strength of a chemically bonded CNT–CF hierarchical structure by detaching individual CNT from the CF substrate and simultaneously recording the force–displacement characteristics in a scanning electron microscopy equipped with a nano-manipulator. We observed a relatively wide distribution of the maximum forces at complete detachment for different grafted CNTs, which ranges from below the van der Waals (vdW) force existing at the CNT–CF interface up to 7 times higher than that. For a typical configuration where a CNT is partially anchored on a CF, we obtained grafting strengths in the range of 5–90 MPa, which are dominated by the vdW force as well as other factors such as chemical bonding. Our results, based on the measurements at individual nanostructure level, might be useful for designing and fabrication of high performance hierarchical composites.     

Toward improved mechanical performance of multiscale carbon fiber and carbon nanotube epoxy composites

A novel class of multiscale epoxy composites was developed containing carbon fibers (CFs) and multiwalled carbon nanotubes (MWCNTs) to explore their mutual effect on the mechanical performance of composites. The loading of CFs in composites was kept constant at ∼60 wt%, while the contents of MWCNTs were increased from 0.5 to 2.0 wt%. MWCNTs were functionalized through acid treatment before incorporating into epoxy matrix to promote dispersion quality. The developed composites were characterized microstructurally by scanning electron microscopy and mechanically by tensile, flexural, edgewise compression, and hardness tests. Homogeneous dispersion of MWCNTs was observed until their loading of 1.5 wt%, which enhanced the mechanical performance of composites. Hardness increased up to 47% while tensile, flexural, and edgewise compressive moduli increased to 40%, 16.3%, and 164%, respectively. Moreover, tensile, flexural, and edgewise compressive strengths showed rises of 45%, 15.2%, and 43%, respectively. The fracture strain increased in both the tensile and flexural tests while it decreased in edgewise compressive tests. Increasing the MWCNTs in composites to 2.0 wt% produced their agglomerates and reversed the rising trend in mechanical properties. POLYM. COMPOS., 38:1519–1528, 2017. © 2015 Society of Plastics Engineers     

Modeling of interfacial modification effects on thermal conductivity of carbon nanotube composites

The effect of functionalization of carbon nanotubes on the thermal conductivity of nanocomposites has been studied using a multi-scale modeling approach. These results predict that grafting linear hydrocarbon chains to the surface of a single wall carbon nanotube with covalent chemical bonds should result in a significant increase in the thermal conductivity of these nanocomposites. This is due to the decrease in the interfacial thermal (Kapitza) resistance between the single wall carbon nanotube and the surrounding polymer matrix upon chemical functionalization. The nanocomposites studied here consist of single wall carbon nanotubes in a bulk poly(ethylene vinyl acetate) matrix. The nanotubes are functionalized by end-grafting linear hydrocarbon chains of varying length to the surface of the nanotube. The effect which this functionalization has on the interfacial thermal resistance is studied by molecular dynamics simulation. Interfacial thermal resistance values are calculated for a range of chemical grafting densities and with several chain lengths. These results are subsequently used in an analytical model to predict the resulting effect on the bulk thermal conductivity of the nanocomposite.