Carbon Nanotube Reinforced Epoxy Nanocomposites Research Articles

Micro-end-milling of carbon nanotube reinforced epoxy nanocomposites manufactured using three roll mill technique

Carbon nanotubes (CNTs) have been applied as nano-fillers to improve mechanical, thermal and electrical properties of polymers. Despite near net shape techniques could be used to manufacture nanocomposites, micromachining processes are still necessary to attain high surface quality and dimensional accuracy. Besides, micromachining of nanocomposites could be a potential approach to produce micro-features/components, following the miniaturisation trend of modern manufacturing. Therefore, micro-machining of these relatively new materials needs to be investigated. A comprehensive investigation on machinability of nanocomposites will be presented in terms of chip formation, cutting force, tool wear, surface morphology and surface roughness. Three controlled quantitative factors are investigated at different levels, including filler loading, cutting speed and feed per tooth (FPT). Micro-slotting is performed on an ultra-precision desktop micro-machine tool using uncoated carbide micro-end mill. The additions of multi-walled carbon nanotube (MWCNT) have shown significant effects on the machinability of these epoxy-based nanocomposites including a dramatic reduction in cutting force and machined surface roughness with accelerating tool wear compared with a neat polymer. The irregular cutting force variations when micro-milling epoxy/MWCNT nanocomposites at feed rates below minimum uncut chip thickness (MUCT) (lower than 2 μm) indicating by their fluctuations that different from those in higher feed rates. It possibly shows the impact of size effects that are illustrated by the observations of chip formation, surface morphology, cutting force profiles as well as specific cutting energy calculation.

Three-Dimensional Stochastic Modelling of Wavy Carbon Nanotube Reinforced Epoxy Nanocomposites

Carbon nanotubes (CNTs) are frequently used as the nanoscale filler materials. It has been observed that when they are added to the polymer matrix by a small fraction, they are able to form a strong yet light-weight multifunctional composite materials. Previous studies found these properties to be significantly influenced by the morphology of CNTs embedded in the matrix. In general, long CNTs become wavy and randomly oriented when dispersed in the matrix material. Collectively, they form an interconnected network. Over the past several decades, many theoretical and computational studies have been carried out to capture the mechanics of CNT-reinforced nanocomposites. In most of these models, CNTs are modeled as straight fibers. In addition, a perfect interphase between CNT and epoxy is generally assumed. As such, these models may not capture the realistic morphology of CNT reinforced composites. In the current study, we have developed a method to construct stochastic three-dimensional finite element models of wavy CNT reinforced epoxy nanocomposites. Both aligned type and randomly distributed type are considered. Uniform random distributions are assumed for both waviness and orientation angles of the dispersed CNTs. To study the effect of waviness on the elastic properties, finite element models with maximum CNT waviness angles of 0° (straight), 10° , 20° , and 30° are generated for CNT volume fractions ranging from 0.1 to 1%. A significant decrease in the properties is observed as the maximum allowable waviness angle (θmax) of the embedded CNTs in the epoxy is increased. The obtained values are compared with the theoretical models available in the literature. The three-phase model including CNTs, CNT/epoxy interphase and matrix is also studied to evaluate the effect of ‘soft’ (Ei = 10–75% Em) as well as ‘hard’ interphase (Ei = 110–175% Em) on the composite modulus. These results suggest that due to ineffective load transfer between CNT and epoxy in the presence of CNT waviness, the elastic modulus of the CNT composites is compromised by 4–8%. The modulus is further decreased by nearly 2.5% as the CNT/epoxy interphase modulus decreases by 90%. The ‘hard’ interphase model confirms an efficient load transfer from matrix to CNT fibers, leading to the increase in composite stiffness. It is found that the composite modulus is more sensitive to the ‘soft’ interphase.

Fabrication, characterization, morphological and thermal investigations of functionalized multi-walled carbon nanotubes reinforced epoxy nanocomposites

Carbon nanotubes (CNTs)-based nanocomposites possess potential applications in electronics and actuators components. Herein, the epoxy-based nanocomposites with various weight percent of oxidized, acylated MWCNTs, unmodified and epoxy modified MWCNTs-epoxy (i.e. 0.01, 0.05, 0.1, 0.3, 0.5 wt.%) were successfully synthesized via ultrasonication and fabricated by the solution casting method. The CNTs-reinforced epoxy polymers composites were successfully synthesized by mixing m-MWCNTs with epoxy resin. Different characterization techniques, i.e., Fourier transmission electron microscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and differential thermogravimetric analysis (DTg) were carried out to characterize thermal and morphological stabilities of the nanocomposites. FTIR interpretation revealed the complete curing, as well as good interaction and compatibility between the modified fillers and epoxy resins. The SEM micrographs exhibit that m-MwCNTs-epoxy showed good dispersion, interfacial interaction, crack resistance, and adhesion as compared to u-MwCNTs nanocomposites. From the results, it was concluded that the m-MWCNTs could improve the interfacial adhesion between the MWCNTs and polymeric epoxy resins, thus results in highly enhanced thermal and morphological stabilities of the polymeric epoxy materials.

Analyzing the effects of interphase on the effective damping properties of aligned carbon nanotube-reinforced epoxy nanocomposites using a micromechanical approach

In this work, a micromechanical approach consisting of high-fidelity generalized method of cells (HFGMC) and Mori-Tanaka (M-T) model is proposed to calculate the damping properties of aligned carbon nanotube-epoxy nanocomposites. To determine the resultant directional specific damping coefficients, these models, by applying strain energy approach in the global system utilize each constituent’s specific damping coefficients and mechanical properties. The effects of interphase created in the contact region of the two initial phases—carbon nanotube and polymer matrix—are extensively investigated. Comparative studies show that the micromechanical results are in good agreement with experimental data. One major finding is the thickness and mechanical and damping properties of interphase significantly affect the overall specific damping coefficients of the carbon nanotube-polymer nanocomposites. It is found that by increasing the elastic modulus of the interphase, the longitudinal specific damping property continuously increases, while other components of damping, initially increase and then asymptotically decrease. The damping properties of polymer nanocomposites can be increased by increasing the interphase damping capacity. However, the rise of interphase thickness leads to a reduction of nanocomposite damping properties. Also, the influences of carbon nanotube volume fraction and radius are examined on the damping response of polymer nanocomposites.

Role of interface on damping characteristics of multi-walled carbon nanotube reinforced epoxy nanocomposites

In this report, we propose an experimental approach to determine the role of the epoxy-CNT interface on damping by designing two systems of composites which differ in the interfacial area. The composites are namely ‘dispersed’ and ‘layered’. The CNTs were uniformly distributed in the epoxy matrix of the dispersed nanocomposites. Whereas, in the layered nanocomposite, a layer of CNT was sandwiched between two epoxy sheets. Image threshold technique was adopted to characterize the CNT spread area in the epoxy matrix. The epoxy-CNT interfacial area is assumed to be less than the CNT spread area due to the agglomeration of CNTs. The CNT spread area of dispersed nanocomposites was found to be 30 times higher than that of the layered composite. In addition to this, it is observed with microstructure analysis using scanning electron microscope and transmission electron microscope that the dispersed nanocomposites were comprised of more epoxy-CNT interfaces, and the layered nanocomposites have more CNT-CNT interfaces. At a particular CNT content, at the glass transition temperature, higher dynamic loss factor was characterized with dispersed nanocomposites. The energy dissipating nature of the epoxy-CNT and CNT-CNT interfaces were studied by analyzing the microstructural mechanisms of damping related to the system of composites dealt with this study.

Graphene and carbon nanotube reinforced epoxy nanocomposites: A review

The continuous demand for low weight, economical and high strength materials have been the driving force for the search of new materials. The discovery of carbon nanofillers, viz. graphene (Ga) and carbon nanotubes (CNTs), has brought tremendous revolution in the field of epoxy-based nanocomposites. The extraordinary thermo-mechanical, electrical and flame-retardant properties offered by Ga and CNTs have led to the development of Ga/CNT-epoxy nanocomposites. The paper reviews the research conducted in the last ten years pertaining to the fabrication, characterization and applications of Ga/CNTs-epoxy composites. The major challenges faced by the researchers in developing epoxy nanocomposites for high performance applications are also highlighted. It is revealed by simultaneously reinforcing Ga and CNTs in epoxy, one could resolve major issues like poor dispersion and agglomeration of nanofillers in epoxy, which can help in developing ultra-high-performance nanocomposites. But further research is needed to explore the full potential of Ga/CNTs/epoxy hybrid nanocomposites.

Multiscale modeling of the interface effects in CNT-epoxy nanocomposites

This paper presents a hierarchical multiscale simulation framework for investigating the interface effects in polymer nanocomposites. In this framework, the load transfer ability of the interface in carbon nanotube (CNT)-epoxy nanocomposites is evaluated using molecular dynamics (MD) simulations by adopting an atomistic graphene-polymer interface model in which the cured epoxy matrix with various crosslink densities is constructed by using a dynamic crosslinking algorithm. The interfacial behavior between CNTs and the epoxy matrix has been characterized in both normal opening mode and sliding mode separation in terms of the force-separation responses at the nanoscale. Key factors, e.g. the crosslink density of the epoxy network in the matrix, the system temperature, the separation mode and functionalization, has been investigated on their effects on the load transfer ability of the CNT-epoxy interface. Further, by employing embedded cohesive zone model in finite element analysis, the macroscale effective material properties of the CNT-epoxy nanocomposites have been evaluated under the nanoscale interface effects. It is observed that covalent functionalization between CNT and polymer matrix can dramatically improve the load transfer ability of the interface at the nanocale, thereby enhancing the effective mechanical properties of the nanocomposites at the microscale. This work will assist in deepening our knowledge about the load transfer ability of the interface and the corresponding strengthening mechanisms in CNT reinforced epoxy nanocomposites.

Free, partial, and fully constrained recovery analysis of cold-programmed shape memory epoxy/carbon nanotube nanocomposites: Experiments and predictions

Thermally activated shape memory polymers are typically programmed by initially heating the material above the glass transition temperature ( Tg), deforming to the desired shape, cooling below Tg, and unloading to fix the temporary shape. This process of deforming at high temperatures becomes a time-, labor-, and energy-expensive process while applying to large structures. Alternatively, materials with reversible plasticity shape memory property can be programmed at temperatures well below the glass transition temperature which offers several advantages over conventional programming. Here, the free, partial, and fully constrained recovery analysis of cold-programmed multi-walled carbon nanotube–reinforced epoxy nanocomposites is presented. The free recovery analysis involves heating the temporary shape above Tg without any constraints (zero stress), and for fully constrained recovery analysis, the temporary shape is held constant while heating. The partially constrained recovery behavior is studied by applying a constant stress of 10%, 25%, and 50% of the maximum recovery stress obtained from the completely constrained recovery analysis. The samples are also characterized for their thermal, morphological, and mechanical properties. A non-contact optical strain measurement method is used to measure the strains during cold-programming and shape recovery. The different recovery behaviors are analyzed by using a thermo-viscoelastic–viscoplastic model, and the predictions are compared with the experimental results.

The influence of N-doping types for carbon nanotube reinforced epoxy composites: A combined experimental study and molecular dynamics simulation

In this study, nitrogen doped carbon nanotube reinforced epoxy nanocomposites were characterized through experiments and molecular dynamics (MD) simulation. Carbon nanotubes were functionalized by nitrogen inductively coupled plasma. They were made into a nanocomposite by a solvent-free mixing method. The various characteristics of nanocomposites, including nitrogen doped carbon nanotubes were analyzed by the following experiments: a Raman spectra, an X-ray photoelectron spectroscopy (XPS), quasi-static tensile tests, a scanning electron microscopy (SEM), and a transmission electron microscopy (TEM). In addition, an MD simulation was performed to predict the mechanical properties of nanocomposites and the results were compared to the test measurements. It showed that the effective dispersion of nitrogen doped carbon nanotubes was important to improve the mechanical characteristics of the nanocomposites.

Reversible plasticity shape memory effect in carbon nanotubes reinforced epoxy nanocomposites

Reversible plasticity shape memory (RPSM) property of multi-walled-carbon-nanotube (MWCNT) reinforced epoxy nanocomposites is investigated as an alternative to conventional shape memory programming and for possible applications in self-healing systems. A commercially available structural grade epoxy resin is tailored to realize RPSM effect and the material properties are further enhanced with the addition of MWCNT in the polymer matrix. The samples are characterized for their mechanical, thermal, morphological and crystallographic properties. This paper systematically investigates the effect of MWCNT addition on the properties of the epoxy matrix. To study the RPSM effect, the nanocomposites are programmed by cold drawing and stress relaxation below the glass transition temperature (Tg) and recovered by reheating above Tg. A comprehensive study on the effect of programming conditions like strain rate, strain level and stress relaxation time on the RPSM property is presented. Results reveal that all samples show excellent shape recovery property under various programming conditions. The addition of MWCNT resulted in a significant increase in modulus and strength, decrease in failure strain, increase in Tg and an improvement in RPSM properties like shape fixity, response temperature and recovery speed. As a result, this study shows that by controlling the parameters like glass transition temperature, filler content and the programming conditions, the material can be effectively designed for application in smart structures with shape memory and/or self healing capabilities.

The role of the interphase on the shear induced failure of multiwall carbon nanotubes reinforced epoxy nanocomposites

ABSTRACTMultiwall Carbon Nanotubes (MWCNT) with an elevated aspect ratio were chemically functionalized with amines and two types of epoxide groups. Thermogravimetric analysis and Fourier Transform‐Infrared Spectroscopy (FTIR) analysis corroborated that the functionalization degree was substantial (up to 30 wt %) and the presence of a covalent bond with the MWCNT. The functionalized MWCNT (f‐CNT) were incorporated into an epoxy matrix after its dispersion in the diglycidyl ether of bisphenol A (DGEBA) precursor. To induce a shear failure mode, a short‐beam (SB) experimental setup was implemented. The SB shear strength (SBSS) proved that the functionalization had a strong influence on its value. For the case of pristine CNT, a neutral effect was obtained. A strong detrimental effect (−17.2% ± 9.5) was measured for the amine type f‐CNT and a positive effect (up to 10.9% ± 8.9) was measured of the epoxide type f‐CNT. Fractographic analysis of each formulation was correlated with SBSS performance, proving that the surface texture of the fractured samples was strongly correlated to its value. Furthermore, dynamic mechanical analysis proved that the damping factor and the crosslink molecular weight were correlated with the SBSS performance. A lower full width at half maximum of the damping factor was associated to an improvement of SBSS. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41364.

Reinforcement of epoxy resins with multi-walled carbon nanotubes for enhancing cryogenic mechanical properties

Epoxy resins are widely applied in cryogenic engineering and their cryogenic mechanical properties as important parameters have to be improved to meet the high requirements by cryogenic engineering applications. Carbon nanotubes (CNTs) are regarded as exceptional reinforcements for polymers. However, poor carbon nanotube (CNT)–polymer interfacial bonding leads to the unexpected low reinforcing efficiency. This paper presents a study on the cryogenic mechanical properties of multi-walled carbon nanotube reinforced epoxy nanocomposites, which are prepared by adding multi-walled carbon nanotubes (MWCNTs) to diglycidyl ether of bisphenol-F epoxy via the ultrasonic technique. When the temperature decreases from room temperature to liquid nitrogen temperature (77 K), a strong CNT–epoxy interfacial bonding is observed due to the thermal contraction of epoxy matrix because of the big differences in thermal expansion coefficients of epoxy and MWCNTs, resulting in a higher reinforcing efficiency. Moreover, synthetic sequence leads to selective dispersion of MWCNTs in the brittle primary phase but not in the soft second phase in the two phase epoxy matrix. Consequently, the cryogenic tensile strength, Young's modulus, failure strain and impact strength at 77 K are all enhanced by the addition of MWCNTs at appropriate contents. The results suggest that CNTs are promising reinforcements for enhancing the cryogenic mechanical properties of epoxy resins that have potential applications in cryogenic engineering areas.

Improved mechanical properties of coiled carbon nanotubes reinforced epoxy nanocomposites

Abstract The incorporation of carbon nanotubes in nanocomposites is expected to greatly enhance the physical and mechanical properties of the host polymer matrices due to inherent superior properties of nanotubes, i.e. high aspect ratio, extraordinary mechanical properties, thermal stability, and enhanced electrical conductivity [Harris PJF. Int Mater Rev 2004;49(1):31–43]. To date, there have been a number of reports that focus on the addition of straight nanotubes in polymer matrixes with mixed results. Studies on incorporation of nanotubes with other varying shapes have been few in numbers despite the fact that they have also been demonstrated to have potential applications, especially in the case of coiled nanotubes which is the focus of this report.