Isothermal crystallization behavior and mechanical properties of polylactide/carbon nanotube nanocomposites

Carbon nanotube (CNT)–reinforced polylactide (PLA) nanocomposites were prepared using a melt compounding process employing a twin-screw extruder. The isothermal crystallization kinetics of PLA/CNT nanocomposites according to Avrami’s theory were analyzed using differential scanning calorimetry in the temperature range 90–120 °C. There was a significant dependence of CNT on the crystallization behavior of the PLA matrix. The incorporation of CNT improved effectively the crystallization rate of PLA/CNT nanocomposites through heterogeneous nucleation. The nucleating effect of CNTs which increased the number of nucleation sites and decreased the average spherulite size was confirmed using polarized optical microscopy. The rheological properties of the PLA/CNT nanocomposites were also investigated. Changes in the microstructure of the PLA/CNT nanocomposites occurred by incorporating CNT. Furthermore, the tensile strength/modulus and thermal stability of PLA/CNT nanocomposites were enhanced when a very small quantity of CNT was added. This research accounts for the effect of CNTs, which significantly influenced the isothermal behavior, thermal stability, mechanical, and rheological properties of the PLA/CNT nanocomposites, providing a design guide for PLA/CNT nanocomposites in industrial fields.     

Dispersion and functionalization of carbon nanotubes for polymer-based nanocomposites: A review

Carbon nanotubes (CNTs) hold the promise of delivering exceptional mechanical properties and multi-functional characteristics. Ever-increasing interest in applying CNTs in many different fields has led to continued efforts to develop dispersion and functionalization techniques. To employ CNTs as effective reinforcement in polymer nanocomposites, proper dispersion and appropriate interfacial adhesion between the CNTs and polymer matrix have to be guaranteed. This paper reviews the current understanding of CNTs and CNT/polymer nanocomposites with two particular topics: (i) the principles and techniques for CNT dispersion and functionalization and (ii) the effects of CNT dispersion and functionalization on the properties of CNT/polymer nanocomposites. The fabrication techniques and potential applications of CNT/polymer nanocomposites are also highlighted.     

Nano-silver modified carbon nanotubes to reinforce the copper matrix composites and their mechanical properties

In ensuring the effective load transfer of carbon nanotubes (CNTs) reinforced copper (Cu)-based composites, good and stable interface contact is a key factor. Powder electrodeposition technology is used in the present study to coat silver (Ag) nanoparticles on CNTs for the first time. Subsequently, by ball milling and spark plasma sintering, uniform distribution of CNTs in the Cu matrix and tight Cu/C interface bonding are successfully achieved. It is found that Ag nanoparticles with a size of 5 nm are evenly embedded in the surface of CNTs. The results reveal that the agglomeration of CNTs is prevented by the addition of Ag nanoparticles and the adhesion between CNTs and Cu matrix is enhanced by the formation of coherent interface. Further, the load transfer of composite materials is effectively realized by the pinning effect of Ag particles on CNTs. The tensile strength, elongation, and conductivity of the 0.75 CNT-Ag/Cu samples were 314 MPa, 24.8%, and 93.6% IACS, respectively, which are 40.1%, 818%, and 3.3% higher than those of the CNT/Cu samples, respectively. The present method provides a new direction for the uniform coating powder materials and the synergistic strengthening of metal matrix composites.     

Development of Carbon Nanotube-Reinforced Nickel-Based Nanocomposites Using Laser Powder Bed Fusion

Modern aerospace applications demand the development of high-performance components with advanced materials. The development of nanomaterial-reinforced metal matrix composites is a practical approach to improve properties. Laser powder bed fusion (LPBF) is one of the popular additive manufacturing approaches to fabricating metal parts with complex geometric structures. This research investigates multiwalled carbon nanotube (CNT)-reinforced nickel-based alloy (Haynes 230) nanocomposite for property improvement. Three volumetric concentrations (0%, 2.5%, and 5%) of CNTs in the metal matrix are investigated with different printing parameters. Different characterizations are conducted on the test specimens. Results show that LPBF-printed Haynes 230 with 2.5 vol% CNTs has higher relative density (99.36%) and less porosity compared to those printed with 5 vol% CNTs. Mechanical test results show that LPBF-printed Haynes 230 with 2.5 vol% CNTs has the highest hardness, modulus of elasticity, yield strength, and ultimate strength than those printed with as-received Haynes 230 powder (with 0 vol% CNTs), Haynes 230 with 5 vol% CNTs, and commercial Haynes 230 plates. The strengthening behavior of the CNTs in the metal matrix composites is discussed in this paper. The potential of CNT-reinforced nickel-based nanocomposites for applications requiring materials with outstanding mechanical properties, such as aerospace and defense, is demonstrated.     

Interface tailoring to enhance mechanical properties of carbon nanotube reinforced magnesium composites

This study highlights the use of a metallic coating of nanoscale thickness on carbon nanotube to enhance the interfacial characteristics in carbon nanotube reinforced magnesium (Mg) composites. Comparisons between two reinforcements were targeted: (a) pristine carbon nanotubes (CNTs) and (b) nickel-coated carbon nanotubes (Ni–CNTs). It is demonstrated that clustering adversely affects the bonding of pristine CNTs with Mg particles. However, the presence of nickel coating on the CNT results in the formation of Mg₂Ni intermetallics at the interface which improved the adhesion between Mg/Ni–CNT particulates. The presence of grain size refinement and improved dispersion of the Ni–CNT reinforcements in the Mg matrix were also observed. These result in simultaneous enhancements of the micro-hardness, ultimate tensile strength and 0.2% yield strength by 41%, 39% and 64% respectively for the Mg/Ni–CNT composites in comparison with that of the monolithic Mg.     

Microstructure and mechanical properties of CNT/Ag nanocomposites fabricated by spark plasma sintering

Carbon nanotube/silver (CNT/Ag) nanocomposites include CNT volume fraction up to 10?vol.% were prepared by chemical reduction in solution followed by spark plasma sintering. Multiwalled CNTs underwent surface modifications by acid treatments, the Fourier transform infrared spectroscopy data indicated several functional groups loaded on the CNT surface by acid functionalisation. The acid-treated CNTs were sensitised and activated. Silver was deposited on the surface of the activated CNTs by chemical reduction of alkaline silver nitrate solution at room temperature. The microstructures of the prepared CNT/Ag nanocomposite powders were investigated by high-resolution scanning electron microscopy (HRSEM), transmission electron microscopy and X-ray powder diffraction analysis. The results indicated that the produced CNT/Ag nanocomposite powders have coated type morphology. The produced CNT/Ag nanocomposite powders were sintered by spark plasma sintering. It was observed from the microstructure investigations of the sintered materials by HRSEM that the CNTs were distributed in the silver matrix with good homogeneity. The hardness and the tensile properties of the produced CNT/Ag nanocomposites were measured. By increasing the volume fraction of CNTs in the silver matrix, the hardness values increased but the elongation values of the prepared CNT/Ag nanocomposites decreased. In addition, the tensile strength was increased by increasing the CNTs volume fraction up to 7.5?vol.%, but the sample composed of 10?vol.% CNT/Ag was fractured before yielding.     

Effect of surfactant treatment on thermal stability and mechanical properties of CNT/polybenzoxazine nanocomposites

The mechanical and thermo-mechanical properties of polybenzoxazine nanocomposites containing multi-walled carbon nanotubes (MWCNTs) functionalized with surfactant are studied. The results are specifically compared with the corresponding properties of epoxy-based nanocomposites. The CNTs bring about significant improvements in flexural strength, flexural modulus, storage modulus and glass transition temperature, T_g, of CNT/polybenzoxazine nanocomposites at the expense of impact fracture toughness. The surfactant treatment has a beneficial effect on the improvement of these properties, except the impact toughness, through enhanced CNT dispersion and interfacial interaction. The former four properties are in general higher for the CNT/polybenzoxazine nanocomposites than the epoxy counterparts, and vice versa for the impact toughness. The addition of CNTs has an ameliorating effect of lowering the coefficient of thermal expansion (CTE) of polybenzoxazine nanocomposites in both the regions below and above T_g, whereas the reverse is true for the epoxy nanocomposites. This observation has a particular implication of exploiting the CNT/polybenzoxazine nanocomposites in applications requiring low shrinkage and accurate dimensional control.     

Dual strengthening mechanisms induced by carbon nanotubes in roll bonded aluminum composites

The dual role of carbon nanotubes (CNTs) in strengthening roll bonded aluminum composites has been elucidated in this study. An increase in the elastic modulus by 59% has been observed at 2 vol.% CNT addition in aluminum, whereas tensile strength increases by 250% with 9.5 vol.% CNT addition. CNTs play a dual role in the strengthening mechanism in Al–CNT composite foil, which can be correlated to the degree of dispersion of CNTs in the matrix. Better CNT dispersion leads to improvement of elastic properties. In contrast, CNT clusters in the aluminum matrix impede dislocation motion, causing strain hardening and thus improvement in the tensile strength. Dislocation density of the composites has been computed as a function of CNT content to show the effect on strain hardening of the metal matrix–CNT composite.     

Tensile properties of carbon nanotube reinforced aluminum nanocomposite fabricated by plasma spray forming

Uniaxial tensile tests were performed on plasma spray formed (PSF) Al–Si alloy reinforced with multiwalled carbon nanotubes (MWCNTs). The addition of CNTs leads to 78% increase in the elastic modulus of the composite. There was a marginal increase in the tensile strength of CNT reinforced composite with degradation in strain to failure by 46%. The computed critical pullout length of CNTs ranges from 2.1 to 19.7 μm which is higher than the experimental length of CNT, leading to relatively poor load transfer and low tensile strength of PSF nanocomposites. Fracture surface validates that tensile fracture is governed strongly by the constitutive hierarchical microstructure of the plasma sprayed Al–CNT nanocomposite. The fracture path in Al–CNT nanocomposite occurs in Al–Si matrix adjacent to SiC layer on CNT surface.     

Fabrication and characterization of carbon nanotube reinforced poly(methyl methacrylate) nanocomposites

Multiwall carbon nanotube (CNT) reinforced poly(methyl methacrylate) (PMMA) nanocomposites have been successfully fabricated with melt blending. Two melt blending approaches of batch mixing and continuous extrusion have been used and the properties of the derived nanocomposites have been compared. The interaction of PMMA and CNTs, which is crucial to greatly improve the polymer properties, has been physically enhanced by adding a third party of poly(vinylidene fluoride) (PVDF) compatibilizer. It is found that the electrical threshold for both PMMA/CNT and PMMA/PVDF/CNT nanocomposites lies between 0.5 to 1 wt% of CNTs. The thermal and mechanical properties of the nanocomposites increase with CNTs and they are further increased by the addition of PVDF For 5 wt% CNT reinforced PMMA/PVDF/CNT nanocomposite, the onset of decomposition temperature is about 17 degrees C higher and elastic modulus is about 19.5% higher than those of neat PMMA. Rheological study also shows that the CNTs incorporated in the PMMA/PVDF/CNT nanocomposites act as physical cross-linkers.     

A simple approach to prepare Al/CNT composite: Spread–Dispersion (SD) method

In carbon nanotube (CNT) reinforced metal matrix composites (MMCs), the good dispersion of CNTs in the matrix as well as the processing problems are the major challenges inhibiting the development of these composites. In this study, well-dispersed CNTs reinforced aluminum (Al) matrix nanocomposite was fabricated by a novel Spread–Dispersion (SD) method. Specimens with ultra-fine grain size down to 20 nm were obtained. The tensile strength of the CNT nanocomposite was 66% greater than the base matrix with a minor decrease in ductility. Such enhancement was analyzed on the basis of segregation and uniform distribution of clustered CNTs, disappearance of the CNT-free zones, eliminated porosity, stronger Al/CNT bonding and the retention of CNT graphitic structure.     

A comprehensive study on thermal conductivities of wavy carbon nanotube-reinforced cementitious nanocomposites

The thermal conductivities of cementitious nanocomposites reinforced by wavy carbon nanotubes (CNTs) are determined by the effective medium (EM) micromechanics-based method. The nanocomposite is composed of sinusoidally wavy CNTs as reinforcement and cement paste as matrix. The interfacial region between the CNTs and cementitious material is considered in the analysis. The effects of volume fraction and waviness parameters of CNTs, interfacial thermal resistance, type of CNTs placement within the matrix including aligned or randomly oriented CNTs, cement paste properties on the thermal conductivity coefficients of the nanocomposite are studied. The estimated values of the model are in very good agreement with available experimental data. Two parameters of CNT waviness and interfacial region contributions should be included in the modeling to predict realistic results for both aligned and randomly oriented CNT-reinforced nanocomposites. The results reveal that thermal conductivities K₂₂ (transverse in-plane thermal conductivity) and K₃₃ (longitudinal in-plane thermal conductivity) of the nanocomposites are remarkably dependent on the CNT waviness. Also, it is found that the CNT waviness moderately affects the thermal conductivity of a cementitious nanocomposite containing randomly oriented CNTs. However, the non-straight shape of CNTs does not influence the value of thermal conductivity K₁₁ (transverse out of plane thermal conductivity). The achieved results can be useful to guide the design of cementitious nanocomposites with optimal thermal conductivity properties.     

Microstructure and properties of polyurethane nanocomposites reinforced with methylene-bis-ortho-chloroanilline-grafted multi-walled carbon nanotubes

Methylene-bis-ortho-chloroanilline (MOCA), an excellent cross-linker widely used to prepare cured polyurethane (PU) elastomers with high performance, was used to modify a multi-walled carbon nanotube. PU/carbon nanotube (CNT) nanocomposites were prepared by incorporation of the MOCA-grafted CNT into PU matrix. Fourier transform infrared spectra have shown that the modified CNTs have been linked with PU matrix. The microstructure of composites was investigated by Field-Emission Scanning Electron Microscopy. The results of Dynamic Mechanical Thermal Analysis and Differential Scanning Calorimetry have investigated the grafted CNTs as cross-linker in the cured composites. The studies on the thermal and mechanical properties of the composites have indicated that the storage modulus and tensile strength, as well as glass transition temperature and thermal stability are significantly increased with increasing CNT content.     

Thermal Conductivity Behavior of Carbon Nanotubes Reinforced Copper Matrix Composites

Carbon nanotubes (CNT) exhibit excellent thermal conductivity.Therefore they are potential reinforcements in composites materials for thermal management applications,where high thermal conductivity and low coefficient of thermal expansion (CTE) are required.In the present study,CNT/Cu composites containing CNTs varying from 0 vol.％ to 15 vol.％ were prepared,and their thermal conductivity behavior was studied in detail.The results indicated that the thermal conductivity of the composites shows no enhancement by the incorporation of CNTs.The presence of interfacial thermal resistance and high level of porosity are the main reasons for this low thermal conductivity.The well dispersed 0-10 vol.％ CNTs composites show a very close to the thermal conductivity of Cu.However,the addition of 15 vol.％ CNTs results in a rather low thermal conductivity of CNT/Cu composites due to the presence a high level of porosity induced by the formation of CNT clusters.The present paper also claims that a further substantial enhancement in thermal conductivity is only possible if the nanotubes are randomly oriented in the plane or if they are all aligned in one direction,for which the processing of CNTs-aligning in metal matrix should be developed.     

Vibration damping characteristics of carbon fiber-reinforced composites containing multi-walled carbon nanotubes

Vibration damping characteristic of nanocomposites and carbon fiber reinforced polymer composites (CFRPs) containing multiwall carbon nanotubes (CNTs) have been studied using the free and forced vibration tests. Several vibration parameters are varied to characterize the damping behavior in different amplitudes, natural frequencies and vibration modes. The damping ratio of the hybrid composites is enhanced with the addition of CNTs, which is attributed to sliding at the CNT-matrix interfaces. The damping ratio is dependent on the amplitude as a result of the random orientation of CNTs in the epoxy matrix. The natural frequency shows negligible influence on the damping properties. The forced vibration test indicates that the damping ratios of the CFRP composites increase with increasing CNT content in both the 1st and 2nd vibration modes. The CNT-epoxy nanocomposites also show similar increasing trends of damping ratio with CNT content, indicating the enhanced damping property of CFRPs arising mainly from the improved damping property of the modified matrix. The dynamic mechanical analysis further confirms that the CNTs have a strong influence on the composites damping properties. Both the dynamic loss modulus and loss factor of the nanocomposites and the corresponding CFRPs show consistent increases with the addition of CNTs, an indication of enhanced damping performance.     

Freeze cast carbon nanotube-alumina nanoparticle green composites

CNT-Al₂O₃ nanoparticle suspensions without and with sodium dodecyl sulfate (SDS) were freeze-cast into green samples. SDS drastically improves Carbon nanotube (CNT) dispersion and CNT-Al₂O₃ nanocomposite homogeneity. Green density of the CNT-Al₂O₃ nanocomposites decreases with CNT addition. Green strength of the CNT-Al₂O₃ nanocomposites increases with the CNT content when CNTs are well separated. The CNT-Al₂O₃ nanocomposites show medium energy fracture mode during equibiaxial flexural strength testing and change color in response to CNT content and distribution in the Al₂O₃ nanoparticle matrix.     

Al/CNT nanocomposite fabrication on the different property of raw material using a planetary ball mill

In recent years, significant research has been focused on the development of carbon nanotube (CNT) reinforced aluminum nanocomposites, which are quickly emerging because of their lightweight, high strength and other mechanical properties. The potential applications of these composites include the automotive and aerospace industries. In this study, powder metallurgy techniques are employed to fabricate aluminum (Al)/CNT nanocomposites with different raw material properties with optimized conditions. We successfully fabricated three different samples, including un-milled Al, un-milled Al with CNT and milled Al with CNT nanocomposites, in the presence of additional CNTs with various experimental conditions using a planetary ball mill. Scanning electron microscopy and field emission scanning electron microscopy are used to evaluate the particle morphology and CNT dispersion. The CNTs are well dispersed on the surface of the fabricated milled Al with CNT nanocomposites than un-milled Al with CNT nanocomposites for milling. The fabricated Al/CNT nanocomposites are processed by a compacting, sintering and rolling process. Vickers hardness measurements are used to characterize the mechanical properties. The hardness of the Al/CNT nanocomposites are improved milled Al with CNT nanocomposite compared other fabricated composites.     

Hygro-Thermo-Electric Properties of Carbon Nanotube Epoxy Nanocomposites with Agglomeration Effects

In the present study, the effective electric, thermal, and moisture properties of carbon nanotube (CNT) epoxy composites are derived by considering the agglomeration effect of CNT concentrations in the epoxy matrix. In this direction, the Voigt and Reuss homogenization method is adopted in the derivations. It is well known from experiments that the CNT thermal and electrical conductivities and the epoxy hygro-thermal expansion coefficients have significant effects on the behavior of CNT nanocomposites. Moreover, it has been experimentally proved that the agglomeration of CNTs in the matrix with high and low concentrations of the CNTs certainly affects the resistivity and, hence, the thermal expansion properties. Therefore, the effective elastic, thermal, electrical, and moisture properties for the randomly distributed CNTs in the matrix has been derived in terms of the agglomeration volume fractions of CNTs. In the effective relations, a single agglomeration parameter is considered to be active for a given potential. The results of variation in the hygro-electro-thermal properties due to change in CNT volume fraction as well as agglomeration parameters have been presented. The results and observation show that CNT agglomeration has a strong influence on the effective hygro-thermo-electric properties of the nanocomposites.     

Achieving Good Strength–Plasticity Compatibility in Cu Composites via Carbon Nanotube-Induced Heterogeneous Bimodal Structure

Traditionally, metal matrix composites reinforced with uniformly dispersed carbon nanotube (CNT) have shown significant enhancement in strength, but always accompanied by the deterioration of uniform elongation (UE). Herein, a novel strategy is proposed to achieve the prominent strength–ductility combination of CNT-reinforced Cu composites. The strategy makes use of the architecture design via mixing the CNT/Cu composite powders (prepared by the molecular-level mixing method) with coarse-grained Cu powders. The bulk composites with a controlled inhomogeneous microstructure are designed and fabricated, in which the reinforcing phase is inhomogeneously distributed at the microscale but homogeneous at the macroscale. The effects of fine and coarse grain proportions on the microstructure evolution and plastic deformation capacity of bimodal-grained Cu composites are investigated. When the mixed ratio of refined CNT/Cu powder to coarse-grained Cu is 1:1, the ultimate tensile strength (UTS) and UE of bimodal-grained Cu composites are 384 MPa and 26.9%, respectively. Such good strength–plasticity compatibility is attributed to the combined effects of hetero-deformation-induced (HDI) stress and CNT strengthening mechanisms. This study provides insights for evading the strength–ductility trade-off in high-performance metal matrix composite by architecture design.     

球磨工艺对原位合成碳纳米管增强铝基复合材料微观组织和力学性能的影响

将原位化学气相沉积法合成的碳纳米管(CNTs)与铝的复合粉末进行球磨混合,进而粉末冶金制备CNTs/Al复合材料,研究球磨工艺对复合材料的微观组织和力学性能的影响。结果表明:球磨过程中不添加过程控制剂所得到的复合材料力学性能优异;随着球磨时间的增加,CNTs逐步分散嵌入铝基体内部,复合材料的组织也变得更加致密均匀。CNTs/Al复合材料的硬度和抗拉强度均随球磨时间的延长持续增加,但是伸长率先增后减。经90min球磨的CNTs/Al复合材料展现了强韧兼备的特点,其硬度和抗拉强度较原始纯铝提高了1.4倍和1.7倍,并且具有17.9%的高伸长率。