CNT-grafted Carbon Fibers Research Articles

Effect of carbon nanotube surface modification on tensile properties of carbon fiber epoxy impregnated bundle composites

The effect of carbon nanotubes (CNTs) on the tensile properties of polyacrylonitrile (PAN)-based carbon fiber epoxy impregnated bundle composites was investigated. To grow CNTs on the carbon fibers, the following catalysts were selected: Ferrocene ([Fe(C5H5)2]) catalyst applied to the bundles using chemical vapor deposition (CVD), and iron (III) nitrate nonahydrate ([Fe(NO3)3•9H2O]) catalyst applied by dipping the bundles in ethanol solutions of different concentrations ranging from 0.01 to 0.5 M. For bundle composites with Fe(C5H5)2-catalyzed CNTs, the Weibull modulus was 29% higher than the as-received state, although the tensile strength is almost unchanged. The Weibull modulus is 9–39% higher than the as-received state for Fe(NO3)3•9H2O catalyst solutions in the range 0.01–0.3 M, while it decreases by 22–32% for 0.4–0.5 M solutions. The tensile strength is lower in both cases; 4–7% lower for 0.01–0.3 M solutions and 14–17% lower for 0.4–0.5 M solutions. Fe(NO3)3•9H2O catalysts 0.1 M solutions gives the best combination of tensile strength and Weibull modulus improvement. The results also show that for each type of CNT-grafted and as-received PAN-based carbon fibers, an almost linear relation between the Weibull modulus and average tensile strength on the log-log scale is observed. This relation indicates that Fe(C5H5)2 catalyst-grafting of CNTs gives better tensile strength and Weibull modulus results.

Improving delamination resistance of carbon fiber reinforced polymeric composite by interface engineering using carbonaceous nanofillers through electrophoretic deposition: An assessment at different in‐service temperatures

AbstractIn this article, modification of carbon fiber surface by carbon based nanofillers (multi‐walled carbon nanotubes [CNT], carbon nanofibers, and multi‐layered graphene) has been achieved by electrophoretic deposition technique to improve its interfacial bonding with epoxy matrix, with a target to improve the mechanical performance of carbon fiber reinforced polymer composites. Flexural and short beam shear properties of the composites were studied at extreme temperature conditions; in‐situ cryo, room and elevated temperature (−196, 30, and 120°C respectively). Laminate reinforced with CNT grafted carbon fibers exhibited highest delamination resistance with maximum improvement in flexural strength as well as in inter‐laminar shear strength (ILSS) among all the carbon fiber reinforced epoxy (CE) composites at all in‐situ temperatures. CNT modified CE composite showed increment of 9% in flexural strength and 17.43% in ILSS when compared to that of unmodified CE composite at room temperature (30°C). Thermomechanical properties were investigated using dynamic mechanical analysis. Fractography was also carried out to study different modes of failure of the composites.

Enhanced Surface Energetics of CNT-Grafted Carbon Fibers for Superior Electrical and Mechanical Properties in CFRPs.

Surface enhancement of components is vital for achieving superior properties in a composite system. In this study, carbon nanotubes (CNTs) were grown on carbon fiber (CF) substrates to improve the surface area and, in turn, increase the adhesion between epoxy-resin and CFs. Nickel (Ni) was used as the catalyst in CNT growth, and was coated on CF sheets via the electroplating method. Surface energetics of CNT-grown CFs and their work of adhesion with epoxy resin were measured. SEM and TEM were used to analyze the morphology of the samples. After the optimization of surface energetics by catalyst weight ratio (15 wt.% Ni), CF-reinforced plastic (CFRP) samples were prepared using the hand lay-up method. To validate the effect of chemical vapor deposition (CVD)-grown CNTs on CFRP properties, samples were also prepared where CNT powder was added to epoxy prior to reinforcement with Ni-coated CFs. CFRP specimens were tested to determine their electrical resistivity, flexural strength, and ductility index. The electrical resistivity of CNT-grown CFRP was found to be about 9 and 2.3 times lower than those of as-received CFRP and CNT-added Ni-CFRP, respectively. Flexural strength of CNT-grown Ni-CFRP was enhanced by 52.9% of that of as-received CFRP. Interestingly, the ductility index in CNT-grown Ni-CFRP was 40% lower than that of CNT-added Ni-CFRP. This was attributed to the tip-growth formation of CNTs and the breakage of Ni coating.

Improved tensile strength of carbon nanotube-grafted carbon fiber reinforced composites

Increased tensile strength of carbon nanotube (CNT)-grafted carbon fiber (CF) composites has been reported, but the mechanism of this increase is not yet clear. In this study, CNT-grafted CF unidirectional (UD) and woven composites were fabricated using a low-temperature chemical vapor deposition (CVD) and resin transfer molding. Two types of CNTs (short and thin, long and thick) were successfully grown and grafted to CFs without degrading the CFs in the preforms. The CNT-grafted CFs exhibited increased interfacial shear strength (IFSS) similarly regardless of the CNT type. Interestingly, however, long and thick CNT-grafted CF UD and woven composites exhibited significant increases in tensile strength (about 20% and 30%), suggesting other mechanisms besides increased IFSS. The splitting crack initiation under the mixed mode condition was quantitatively characterized for the CNT-grafted CF UD composites, demonstrating that long and thick CNTs delayed the splitting crack initiation. Delayed fiber splitting and increased IFSS were concluded to be the main sources of increased tensile strength of CNT-grafted CF composites.

Effects of Water Absorption on the Fiber–Matrix Interfacial Shear Strength of Carbon Nanotube-Grafted Carbon Fiber Reinforced Polyamide Resin

Carbon fiber reinforced thermoplastics (CFRTPs) are expected to be used for the structural parts of automobiles and aircraft due to their mechanical properties, such as high specific stiffness, high specific strength, short molding times and high recyclability. The fiber/matrix interface of the composite plays an important role in transmitting stress from the matrix to the reinforcing fibers. It was reported that grafting of carbon nanotubes (CNTs) on the carbon fiber can improve the fiber/matrix interfacial property. We have reported that CNTs, which are directly grafted onto carbon fiber using Ni as the catalyst by the chemical vapor deposition (CVD) method, can improve the fiber/matrix interfacial shear strength (IFSS) of carbon fiber/polyamide 6 (PA6). For practical use of CFRTPs, it is important to clarify the effects of water absorption on the mechanical properties of the composite material. In this study, the effects of water absorption on the fiber–matrix interfacial shear strength (IFSS) of carbon fiber reinforced polyamide resin and CNT-grafted carbon fiber reinforced polyamide resin were clarified by the single fiber pull-out test for specimens preserved in air, then in water for 24 h and re-dried after water absorption. The IFSS of carbon fiber/PA6 was significantly decreased by water absorption. In contrast, CNT-grafted carbon fiber/PA6 showed smaller degradation of the IFSS by water absorption.

Plasma Polypyrrole Coated Hybrid Composites with Improved Mechanical and Electrical Properties for Aerospace Applications

This paper deals with the dielectric barrier discharge assisted continuous plasma polypyrrole deposition on CNT-grafted carbon fibers for conductive composite applications. The simultaneous effects of three controllable factors have been studied on the electrical resistivity (ER) of these two material systems based on multivariate experimental design methodology. A posterior probability referring to Benjamini-Hochberg (BH) false discovery rate was explored as multiple testing corrections of the t-test p values. BH significance threshold of 0.05 was produced truly statistically significant coefficients to describe ER of two material systems. A group of plasma modified samples was chosen to be used for composite manufacturing to drive an assessment of interlaminar shear properties under static loading. Transversal and longitudinal electrical resistivity (DC, omega = 0) of composite samples were studied to compare both the effects of CNT grafting and plasma modification on ER of resultant composites.

Novel Flexible Composites Reinforced with CNT-Grafted Carbon Fibers

ABSTRACTNovel flexible composites were received by modification of polyurethane-carbon fiber interface. The modification was done by carbon nanotube grafting onto a surface of the fiber. The almost inevitable grafting-induced deterioration of the fiber properties was avoided due to sophisticated grafting technique, which includes introduction of a protective aluminium oxide layer. Re-enforced composites were fabricated with polyurethane as a matrix. The measurement of interfacial shear strength (IFSS) was used for estimation of polymer-fiber interface properties. It was shown that IFSS increased more than twice due to nanotube grafting. Thermal conductivity and mechanical properties enhancement was registered for composites with modified interface. Significant improvement of delamination resistance was proven for composites with modified polymer-fiber interface.

Communication—Catalyst Study on the Large-Scale Preparation of Carbon Nanotube-Grafted Carbon Fibers with High Tensile Strength

This article aimed at development of a catalyst for the highly efficient preparation of carbon nanotube (CNT)-grafted carbon fibers (CFs) with high mechanical properties by using chemical vapor deposition (CVD). Based on an innovative technique for the uniform coating of catalyst on the CF surface, the influence of catalyst type on the morphology and mechanical properties of CNT-grafted CFs has been systematically studied. It was found that trace addition of Cu can significantly enhance the catalytic activity of Fe catalyst, the corresponding tensile strength of final CNT-grafted CFs is 12.0% higher than the untreated CFs.

High efficient preparation of carbon nanotube-grafted carbon fibers with the improved tensile strength

An innovative technique has been developed to obtain the uniform catalyst coating on continuously moving carbon fibers. Carbon nanotube (CNT)-grafted carbon fibers with significantly improved tensile strength have been succeeded to produce by using chemical vapor deposition (CVD) when compared to the tensile strength of untreated carbon fibers. The critical requirements for preparation of CNT-grafted carbon fibers with high tensile strength have been found, mainly including (i) the obtainment of uniform coating of catalyst particles with small particle size, (ii) the low catalyst-induced and mechano-chemical degradation of carbon fibers, and (iii) the high catalyst activity which could facilitate the healing and strengthening of carbon fibers during the growth of CNTs. The optimum growth temperature was found to be about 500°C, and the optimum catalyst is Ni due to its highest activity, there is a pronounced increase of 10% in tensile strength of carbon fibers after CNT growth at 500°C by using Ni catalyst. Based on the observation from HRTEM images, a healing and crosslink model of neighboring carbon crystals by CNTs has been formulated to reveal the main reason that causes an increase in tensile strength of carbon fibers after the growth of CNTs. Such results have provided the theoretical and experimental foundation for the large-scale preparation of CNT-grafted carbon fibers with the improved tensile strength, significantly promoting the development of CNT-grafted carbon fiber reinforced polymer composites.

Manufacture of Carbon Nanotube-Grafted Carbon Fiber Reinforced Thermoplastic Composites

Carbon fiber reinforced composites (CFRCs) have been used in various high-end industries due to their outstanding specific mechanical properties. Recently, carbon nanotube (CNT)-grafted carbon fibers (CFs) made via direct growth has emerged as an advanced and hierarchical reinforcement that can improve the reinforcing effect of CFs in CFRCs. On the other hand, CF reinforced thermoplastic composites (CFRTPs) have attracted much attention because of their quick and mass production capability, e.g., which is important for automotive part manufacturing. Here, we report on the manufacture of CFRTPs using CNT-grafted CFs and their mechanical properties. First, the interfacial shear strength of CNT-grafted CFs with thermoplastic resins was characterized to demonstrate improved interfacial properties due to the CNTs grafted on CFs. Then, the composites were manufactured in two ways; polymer nanoparticles and in-situ polymerization. Polymer nanoparticles were used to improve the interfacial properties due to their small size and good mechanical locking with CF surfaces. In-situ polymerization was also used to manufacture CFRTPs, i.e., monomers with catalyst were transferred into CNT-grafted CF fabric preform using vacuum assisted resin transfer molding and then polymerized into solid matrix. This in-situ polymerization enabled the manufacture of CNT-grafted CF thermoplastic composites by overcoming the difficulties of filling the surface of CNT-grafted CFs with thermoplastic polymers. Finally, the mechanical, thermal, electrical, and damping properties of CNT-grafted CF thermoplastic composites were characterized and compared with their thermoset composites.

J0450401 熱CVD法によるCNT析出炭素繊維強化複合材料の力学特性評価

It is well known that grafting carbon nanotubes (CNTs) on the reinforced fiber surface modifies fiber/matrix interface adhesion. In this study, the mechanical properties of unidirectional FRP using the CNT-grafted pitch-based carbon fiber were investigated. CNTs were grafted on the pitch-based carbon fiber surface using thermal chemical deposition (TCVD) method at 750℃. First, the single fiber tensile tests were conducted to examine the mechanical properties of the CNT-grafted carbon fibers. From the results, the mechanical properties of the CNT-grafted carbon fiber were decreased compared with as-received fiber. This degradation was caused by an exposure of the carbon fiber surface and a dissolution of iron particles into the carbon fiber surfaces under the high temperature condition of TCVD method. Moreover, static tensile tests were performed in unidirectional CFRP to investigate the mechanical properties of the CNT-grafted unidirectional CFRP. For these tests, specimens with fibers oriented at longitudinal (0°) or transverse (90°) angle from the load direction were prepared. From the results, the mechanical properties of the CNT-grafted unidirectional CFRP were decreased in longitudinal direction compared with as-received CFRP due to the degradation of the mechanical properties in CNT-grafted carbon fibers. On the other hand, it was revealed that the mechanical properties of the CNT-grafted unidirectional CFRP were increased in transverse direction compared with as-received CFRP. This enhancement was mainly due to a relaxation of stress concentration at the edge of carbon fiber by the constitution of CNT/epoxy nanocomposites around the carbon fibers.

A facile method for preparing CNT-grafted carbon fibers and improved tensile strength of their composites

Carbon nanotube (CNT)-grafted carbon fibers (CFs) have emerged as new reinforcements for improving the mechanical properties of CF-reinforced composites but such enhancement in macroscale composites has not been realized. This paper reports a facile method for preparing CNT-grafted CFs and improving the tensile strength of their composites. A CNT/polyacrylonitrile solution was sprayed onto the surface of the CF woven fabrics, and the CNTs were grafted by a thermal treatment at 300°C. CNT-grafted CF composites were fabricated using the CNT-grafted CF woven fabrics using a vacuum-assisted resin transfer molding process with epoxy resin. The CNT-grafted CF composite exhibited 22% enhancement in the tensile strength compared to that of the pristine CF composite. Fracture surfaces of the CNT-grafted CF composites showed that the grafted CNTs obstructed the propagation of micro-cracks and micro-delamination around the CFs and also yarn boundaries, resulting in improved tensile strength of CNT-grafted CF composites.

Tensile Properties and Fracture Behavior of Different Carbon Nanotube-Grafted Polyacrylonitrile-Based Carbon Fibers

The tensile properties and fracture behavior of different carbon nanotube (CNT)-grafted polyacrylonitrile-based (T1000GB) single carbon fibers were investigated. Grafting of CNTs was achieved via chemical vapor deposition (CVD). When Fe(C5H5)2 (also applied via CVD) was used as the catalyst, the tensile strength and Weibull modulus of the carbon fibers were improved, possibly due to the growth of dense CNT networks on the carbon fibers, which may have led to a reduction in the number of strength-limiting defects. Separately, at lower concentrations of an Fe(NO3)3·9H2O catalyst in ethanol, which was applied via dipping, the tensile strength of CNT-grafted fibers was nearly identical to that of the as-received fibers, although the Weibull modulus was higher. For higher concentrations of the Fe(NO3)3·9H2O catalyst, however, the tensile strength and the Weibull modulus were lower than those for the as-received material. Although the density of the CNT network increased with the concentration of the Fe(NO3)3·9H2O catalyst in the ethanol solution, heating of the ethanolic Fe(NO3)3·9H2O catalyst solution generated nitric acid (HNO3) due to decomposition, which damaged the fiber surfaces, resulting in an increase in the number of flaws and consequently a reduction in the tensile strength. Therefore, the tensile strength and Weibull modulus of CNT-grafted carbon fibers vary due to the combination of these effects and as a function of the catalyst concentration.

カーボンナノチューブ/炭素繊維高分子系ハイブリッド材料

The tensile properties of carbon fiber (CF) reinforced polymer matrix composites incorporating carbon nanotubes (CNT) sheet (CNT sheet/CF epoxy hybrid composites) and CNT-grafted CF (CNT-grafted CF polyimide hybrid composites) were investigated. For the CNT sheet/CF epoxy hybrid composites, the tensile modulus of hybrid composites was higher than that in the as-received state. The tensile strength of CNT sheet/polyacrylonitrile (PAN)-based CF hybrid composite was lower than that in the as-received state and the tensile strength of CNT sheet/pitch-based CF hybrid composite was higher than that in the as-received state. On the other hand, for the CNT-grafted CF polyimide hybrid composites, the tensile modulus of hybrid composites was higher than that in the as-received state and tensile strength of hybrid composites was almost similar to that in as-received state.

Interfacial studies of carbon fiber/epoxy composites using single fiber fragmentation test

Single fiber fragmentation tests were carried out to measure the properties of the fiber-matrix interface in several carbon fiber (CFs)/epoxy composite systems. Four kinds of CFs were studied: (1) primary CFs (used as received); (2) desized CFs (sizing removed through thermal treatment); (3) resized CFs (deposited with epoxy sizing by solution); (4) carbon nanotube (CNT)-grafted CFs (grown with CNTs using a chemical vapour deposition method). The interfacial shear strength decreased by around 30% for the desized CFs and the CNT-grafted CFs compared with the pristine CFs. The value of interfacial shear strength for the resized CFs was 20% larger than that of the desized CFs. There is a good agreement between the results of single fiber fragmentation tests and that of contact angle tests.

Comparison of chemical vapor deposition and chemical grafting for improving the mechanical properties of carbon fiber/epoxy composites with multi-wall carbon nanotubes

By engineering the fiber/matrix interface, the properties of the composite can be changed significantly. In this work, we increased the effective surface area of the fiber/matrix interface, to facilitate additional stress transfer between fibers and matrix, by grafting carbon nanotubes on to carbon fibers (in the form of carbon fabric) by two different methods: (1) chemical vapor deposition (CVD) method and (2) a purely chemical method. With the CVD process, carbon nanotubes (CNT) were directly grown on carbon fiber substrate using chemical vapors. For the chemical method, CNT with carboxyl groups were grafted on functionalized carbon fiber via a chemical reaction. The morphology of CNT/carbon fibers was examined by scanning electron microscope (SEM) which revealed uniform coverage of carbon fibers with CNT in both of CVD method and chemical grafting method. CNT-grafted woven carbon fibers were used to make carbon/epoxy composites, and their mechanical properties were measured using three-point bending and tension tests which showed that those with CNT-grafted carbon fiber reinforcements using the CVD process has 11 % higher tensile strength compared to those containing carbon fibers modified with the chemical method. Also, composites with CNT-grafted carbon fibers with chemical method showed 20 % higher tensile strength compared to composites with unmodified carbon fibers. The results of tensile test revealed that both CVD and chemical grafting could significantly improve the mechanical properties of the carbon fiber composites.

The effect of surface modification with carbon nanotubes upon the tensile strength and Weibull modulus of carbon fibers

Carbon fibers are widely used as reinforcements in composite materials because of their high specific strength and modulus. Today, a number of ultrahigh strength polyacrylonitrile (PAN)-based (more than 6 GPa), and ultrahigh modulus pitch-based (more than 900 GPa) carbon fibers have been commercially available. In contrast, carbon nanotube (CNT) with the extremely high tensile strength have attracted attention as reinforcements. An interesting technique to modify the carbon fiber is CNT grafting on the carbon fiber surface. CNT-grafted carbon fibers offer the opportunity to add the potential benefits of nanoscale reinforcement to well-established fibrous composites to create micro-nano multiscale hybrid composites. In the present study, the tensile properties of CNT grown on T1000GB PAN- and K13D pitch-based carbon fibers have been investigated. Single filament tensile test at gauge lengths of 1, 5, and 25 mm were conducted. The effect of gauge length on tensile strength and Weibull modulus of CNT-grafted PAN- and pitch-based carbon fibers were evaluated. It was found that grafting of CNT improves the tensile strength and Weibull modulus of PAN- and pitch-based carbon fibers with longer gauge length (≥5 mm). The results also clearly show that for CNT-grafted and as-received PAN- and pitch-based carbon fibers, there is a linear relation between the Weibull modulus and the average tensile strength on log–log scale.

Interfacial shear behavior of 3D composites reinforced with CNT-grafted carbon fibers

This paper presents the Molecular Dynamic (MD) models and the simulation results for the shear deformation process of an interface representative cell to develop an understanding of the roles of multi-walled carbon nanotube (MWNT) in enhancing fiber–matrix interfacial properties such as shear modulus and strength. Based on the MD results and the two simple formulae of rule of mixture, the shear modulus and strength of the carbon nanotube (CNT) grafted interface can be predicted. It is shown that there exists a good agreement between the predicted fiber–matrix interfacial shear strength with and without grafted CNTs and these measured from single-fiber micro bond test and single-fiber fragmentation test. The MD simulation also shows the MWNTs’ shear stress cross-section distribution is similar to that of a circular beam in shear with a non-zero shear stress on the neutral plane.

Preparation of vertically aligned carbon nanotube arrays grown onto carbon fiber fabric and evaluating its wettability on effect of composite

Vertically aligned carbon nanotube (CNT) arrays have been grown onto the carbon fiber fabric using a catalytic chemical vapor deposition (CCVD) method. The as-synthesized CNT arrays are about 20μm in height, and the nanotube has a mean inner and outer diameter of 2.6nm, 5.5nm, respectively. The CNT-grafted carbon fabric shows a hydrophobic property with a contact angle over 145°, and the single CNT-grafted carbon fiber shows a sharp increase of dynamic contact angle in de-ionized water from original 71.70° to about 103°, but a little increase does in diiodomethane or E-51 epoxy resin. However, the total surface energy of carbon nanotube-grafted carbon fiber is almost as same as that of as-received carbon fiber. After CNTs growth, single fiber tensile tests indicated a slight tensile strength degradation within 10% for all different lengths of fibers, while the fiber modulus has not been significantly damaged. Compared with the as-received carbon fibers, a nearly 110% increase of interfacial shear strength (IFSS) from 65 to 135MPa has been identified by single fiber pull-out tests for the micro-droplet composite, which is reinforced by as-received carbon fiber or CNT-grafted carbon fiber.