Improved dispersion of carbon nanotubes in aluminum nanocomposites

Carbon Nanotubes (CNT) offer exceptional thermal, electrical and mechanical properties. While an increase in thermal and electrical conductivity can be readily achieved by addition of CNT to a polymer base, the subsequent effect on mechanical properties must be investigated. In this study, nanocomposite samples were manufactured using injection molding process. Multiwall Carbon Nanotube (MWCNT) masterbatch with 15 wt.% MWCNT concentrations were diluted with PA 6/6 pellets to create five different CNT concentration ranging from 3 wt.% in 3 wt.% increments. The neat polymer sample was also manufactured as a control specimen. Mechanical properties such as Young’s modulus, Tensile strength and elongations were determined to see the effect of CNT content on overall properties. Scanning Electron Microscopy (SEM) images were used to evaluate the uniform distribution of CNT in the polymer phase. The results showed that the stiffness increased as the CNT content increased, however, the increase in strength reached a threshold value around 6 wt.% beyond which the strength decreased. It was observed that the elongation decreased significantly by addition of CNT into the polymer. The elongation dropped from an average of 190% for the neat sample to 5% for 15 wt.% CNT content sample. Such decrease in elongation might render the polymer unsuitable for the application it has been designed for. The findings of this study show that improving thermal and electrical properties of polymers does not come without a sacrifice on mechanical properties.

Effect of carbon nanotube (CNT) content on the properties of in-situ synthesis CNT reinforced Al composites

The mechanical properties and strain-induced crystallization (SIC) of elastomeric composites were investigated as functions of the extension ratio (λ), multiwalled carbon nanotube (CNT) content, and carbon black (CB) content. The tensile strength and modulus gradually increase with increasing CNT content when compared with the matrix and the filled rubbers with same amount of CB. Both properties of rubber with CB and CNT show the magnitude of each CNT and CB component following the Pythagorean Theorem. The ratio of tensile modulus is much higher than that of tensile strength because of the CNT shape/orientation and an imperfect adhesion between CNT and rubber. The tensile strength and modulus of the composite with a CNT content of 9 phr increases up to 31% and 91%, respectively, compared with the matrix. Differential scanning calorimetry (DSC) analysis reveals that the degree of SIC increases with an increase in CNT content. Mechanical properties have a linear relation with the latent heat of crystallization (LHc), depending on the CNT content. As the extension ratio increases, the glass-transition temperature (Tg) of the composite increases for CB- and CNT-reinforced cases. However, the LHc has a maximum of λ = 1.5 for the CNT-reinforced case, which relates to a CNT shape and an imperfect adhesion with rubber. Based on these results, the reinforcing mechanisms of CNT and CB are discussed.

Although ordinary Portland cement (OPC) is one of the most widely used construction materials in the world, its relatively weak tensile strength and fracture resistance limit wider structure applications. Carbon nanotubes (CNTs), having been identified as one of the strongest and stiffest materials on earth, are attractive candidates as nano-filaments in reinforcing OPC. The investigation of CNT reinforced OPC composites (CNT-OPC) is at a relatively early stage, and very limited research regarding the effectiveness of CNTs in enhancing the tensile strength or fracture toughness of OPC are available in open literature. The published results on testing of the CNT reinforcing effect often show large variations and sometimes contradict each other. Therefore, there is a significant need for further studies in this area to improve understanding of the reinforcing behaviour of CNTs in cement matrix, including dispersion of CNTs and the effect of CNT on OPC paste in terms of hydration, microstructure, tensile strength and fracture properties. This study builds on the earlier research on CNT reinforcement of the mechanical properties of OPC paste in Duan’s group in the Department of Civil Engineering at Monash University. Specifically, the objectives of this study are (1) development of high mechanical performance CNT reinforced OPC paste by considering the effect of dispersion and concentration of CNTs within OPC matrix, and (2) investigation of the reinforcing mechanisms of CNTs in cement matrix by estimating the post-peak softening behaviour of CNT-OPC paste and the interfacial bond strength between CNTs and cement matrix. In order to develop high performance CNT reinforced OPC paste, the dispersion and concentration of CNTs were studied. The combinations of chemical functionalisation (COOH functional groups on CNT surface), a polycarboxylate-based cement compatible superplasticiser (PC), and sufficient ultrasonication energy have been found essential to achieving homogeneous dispersion of CNTs in cement paste. An effective PC to CNT mass ratio of 8 is recommended to ensure effective dispersion of CNTs, at the same time maintaining satisfactory workability of CNT-OPC paste. Moreover, a CNT dosage-independent optimal ultrasonication energy for achieving mechanically superior CNT-OPC paste was found to be 50 J/ml per unit CNTs-to-suspensions weight ratio. The incorporation of CNTs (of 0.075 wt.% of cement) substantially enhanced the mechanical properties of plain cement. For example, Young’s modulus was improved by 31.5%, flexural strength by 49.9%, and fracture energy by 62.6%. Regarding the reinforcing mechanisms of CNTs within cement paste, the post-peak softening characteristics of CNT-OPC paste were investigated. It was found that the linear post-peak softening characteristics, including initial fracture energy and cohesive tensile strength of plain OPC paste (estimated using size effect tests with the assistance of cohesive crack-based finite element simulation), can be significantly improved by incorporating CNTs. Particularly, the enhancement of cohesive tensile strength may be attributed to the filling of CNTs in the nano-sized colloidal pores and bridging micro-sized capillary pores. On the other hand, the comparable brittleness numbers obtained for CNT-OPC and OPC pastes indicate the minor contribution of CNTs to the ductility of plain OPC paste. Based on cohesive tensile strength, the range of effective interfacial bond strength between CNTs and cement matrix was estimated to be from 9.5 to 24.5 MPa based on a micromechanics-based crack bridging stress-crack separation model for CNT reinforced composites developed in Duan’s group. This result suggests that the introduction of COOH functional group may enhance the interfacial bond property between CNTs and cement matrix, thereby resulting in improved mechanical performances. This project will provide key information to assist other researchers and practitioners to better understand and apply the novel CNT-cement composite with improved mechanical properties to the design of structures and codification.

In initial experiments the effects of aromatic model substances on carbon nanotube (CNT) dispersions in dimethylformamide (DMF) were investigated. Electron‐deficient aromatics interact strongly with CNTs, causing increased agglomeration and sedimentation. Conversely, electron‐donating aromatics stabilize CNT dispersions in DMF. Polymers with electron‐deficient aromatics, such as polydinitrostyrene (PDNS), exhibit a concentration‐dependent effect: low concentrations lead to stabilization of dispersions, while higher concentrations lead to sedimentation. This suggests that such polymers can enhance attraction between the matrix of CNT‐reinforced polymers as well as stabilize the dispersed CNTs. Polycarbonate, modified with polydinitrocarbonate (PDNC) and reinforced with CNTs showed improved mechanical properties. The addition of 6 wt.% CNTs and 6 wt.% PDNC resulted in a notable improvement with a 22% increase in tensile strength, a 29% increase in flexural strength, a 39% increase in Young's modulus and a 47% increase in flexural modulus. This enhancement resulted in an overall mechanical performance comparable to the high‐performance polymer polyetherimide. However, there must be noted, that the addition of PDNC increases the CNT particle size, which can negatively affect mechanical properties. The results highlight the additive's dual role in enhancing adhesive interactions while potentially increasing CNT agglomerate sizes.Highlights Interactions of CNTs dispersed in DMF and various aromatics were investigated. Polydinitrocarbonate (PDNC) was synthesized as a new additive for CNT‐composites. Polycarbonate/CNT‐composites were obtained using extrusion. Test specimens with CNT contents up to 6 wt.% were obtained. Mechanical properties of polycarbonate reached the level of polyetherimide.

In this paper, the dispersion of carbon nanotube (CNT) in ethylene vinyl acetate (EVA) is demonstrated to be significantly improved by the addition of octadecylamine (ODA)-grafted graphene oxide (GO) (GO–ODA). Compared to the CNT/EVA composite, the resultant GO–ODA/CNT/EVA (G–CNT/EVA) composite shows simultaneous increases in tensile strength, Young’s modulus and elongation at break. Notably, the elongation at break of the G–CNT/EVA composite still maintains a relatively high value of 1268% at 2.0 wt % CNT content, which is more than 1.6 times higher than that of CNT/EVA composite (783%). This should be attributed to the homogeneous dispersion of CNT as well as the strong interfacial interaction between CNT and EVA originating from the solubilization effect of GO–ODA. Additionally, the G–CNT/EVA composites exhibit superior electrical conductivity at low CNT contents but inferior value at high CNT contents, compared to that for the CNT/EVA composite, which depends on the balance of CNT dispersion and the preservation of insulating GO–ODA. Our strategy provides a new pathway to prepare high performance polymer composites with well-dispersed CNT.

The dispersion of carbon nanotubes (CNTs) is the bottleneck in CNT-reinforced metal matrix composites. In this work, CNT/Mg composites were prepared by grinding Mg powder and then dispersing CNTs via ball milling and hot pressing. The uniform distribution of Ni-coated CNTs in the matrix was achieved by optimizing the content of CNTs. Scanning electron microscope, high-resolution transmission electron microscopy and X-ray diffraction, optical microscopy, and compression tests were employed. With the CNT content being less than 1%, the CNTs can be evenly distributed in CNT/Mg composites, resulting in a sharp increase in strength. However, with the higher CNT content, the CNTs gradually cluster, leading decreased fracture strain and strength. Furthermore, the coated Ni in the CNTs reacts with the magnesium matrix and completely transforms into Mg2Ni, significantly enhancing the interface bonding. This strong interface bonding and the diffusely distributed Mg2Ni in the matrix significantly strengthen the CNT/Mg composite.

Effect of CNT concentration and agitation on surface heat flux during quenching in CNT nanofluids

One of the major obstacles to the effective use of carbon nanotubes as reinforcements in metal matrix composites is their agglomeration and poor distribution/dispersion within the metallic matrix. In the present work, we use mechanical alloying (MA) to mechanically mix CNT (2 and 5 wt.%) with Al powders. These powders would be used as precursors for subsequent consolidation to generate bulk CNT-Al composites. Hence controlling the initial powder characteristics prior to high temperature consolidation is important. Up to 48 h of milling was employed to investigate the effect of milling time on the particle size, morphology and CNT dispersions. The results show that particle size and morphology vary with milling time and CNT content. Also the addition of process control agents such as methanol can aid in controlling the powder characteristics.

Fiber reinforced polymeric (FRP) composite materials are subjected to different range of crosshead speeds during their in-service life. The work has been focused to investigate the effect of carbon nanotube (CNT) addition in glass fiber reinforced polymer (GFRP) composite on tensile behavior. The Control GFRP composites and CNT modified composites were tested at different crosshead speeds viz. 1, 10, 100 mm/min. CNT modified matrix was processed with epoxy as a matrix materials and multi-walled carbon nanotube (MWCNT) as a filler with different MWCNT content (i.e. 0.1, 0.3 and 0.5 wt. %). Increase in the CNT content upto 0.3% the tensile strength increasing for all the crosshead speeds as compared to the control GFRP composite. The tensile strength are dependent on the CNT content in GFRP composite. It has been observed that addition of 0.1% CNT and 0.3% CNT enhanced the tensile strength by 6.11% and 9.28% respectively than control GFRP composite. The tensile modulus is found to be mostly unaffected on an optimum CNT content in the GFRP composite. The tensile strength of control GFRP and all CNT modified GFRP composites were found to be crosshead speed sensitive and increased with increasing crosshead speeds in the aforesaid loadings. However, slight decrease in tensile modulus was observed with addition of CNT due to agglomeration of the CNT in the polymer matrix composites. The DSC analysis was also carried out to understand the effect of the CNT content on the glass transition temperature (Tg) of GFRP composites. Different failure patterns of GFRP composite tested at 1, 10, and 100 mm/min crosshead speeds were identified.

Carbon nanomaterials, particularly carbon nanotubes (CNTs), are widely used as reinforcing fillers in rubber composites for advanced mechanical and electrical applications. However, the influence of rubber functionality and its interactions with CNTs remains underexplored. This study investigates electroactive elastomeric composites fabricated with CNTs in two common diene rubbers: natural rubber (NR) and acrylonitrile-butadiene rubber (NBR), each with distinct functionalities. For NR-based composites containing 2 vol% CNTs, mechanical properties, such as elastic modulus (2.24 MPa), tensile strength (12.48 MPa), and fracture toughness (26.92 MJ/m3), show significant improvements of 125%, 215%, and 164%, respectively, compared to unfilled rubber. Similarly, for NBR-based composites, the elastic modulus (5.46 MPa), tensile strength (13.47 MPa), and fracture toughness (82.89 MJ/m3) increase by 94%, 22%, and 65%, respectively, over the unfilled system. Although NBR-based composites exhibit higher mechanical properties, NR systems show more significant improvements, suggesting stronger chemical bonding between NR chains and CNTs, as evidenced by dynamic mechanical, X-ray diffraction, thermogravimetric, and thermodynamic analyses. The NBR-based composite at 1 vol% CNT content exhibits 261% higher piezoresistive strain sensitivity (GF = 65 at 0% ≤ Δε ≤ 200%) compared to the NR-based composite (GF = 18 at 0% ≤ Δε ≤ 200%). The highest gauge factor of 39,125 (1000% ≤ Δε ≤ 1220) was achieved in NBR-based composites with 1 vol% CNT content. However, 1.5 vol% CNT content in NBR provides better strain sensitivity and linearity than other composites. Additionally, NBR demonstrates superior electromechanical actuation properties, with 1317% higher actuation displacement and 276% higher electromechanical pressure compared to NR at an applied electric field of 12 kV. Due to the stronger chemical bonding between the rubber and CNT, NR-based composites are more suitable for dynamic mechanical applications. In contrast, NBR-based CNT composites are ideal for stretchable electromechanical sensors and actuators, owing to the high dielectric constant and polarizable functional groups in NBR.

Preparation of carbon nanotubes/waterborne polyurethane composites with the emulsion particles assisted dispersion of carbon nanotubes

Abstract

Uniform dispersion of carbon nanotubes (CNTs) in metal composites has been by far the most significant challenge in the field of CNT-reinforced metal matrices. This work presents a new dispersion and fabrication technique of Carbon nanotubes (CNTs) reinforced copper (Cu) matrix nanocomposites. A combination of nanoscale dispersion of functionalized CNTs in low viscose media of dissolved paraffin wax under ultrasonication treatment followed by powder injection molding (PIM) technique was adopted. CNTs contents were varied from 0 to 10 vol.%. TEM, EDX, FESEM and Raman spectroscopy analysis were used for materials characterization. Information about the degree of purification and functionalization processes, evidences on the existence of the functional groups, effects of ultrasonication time on the treated CNTs, and microstructural analysis of the fabricated Cu/CNTs nanocomposites were determined. The results showed that the impurities of the pristine CNTs such as Fe, Ni catalyst and the amorphous carbon have been significantly removed after purification process. Meanwhile, FESEM and TEM observations showed high stability of CNTs at elevated temperatures. It also showed an excellent homogeneous dispersion of CNTs in Cu matrix and led to a strong interfacial bonding between Cu particles and individual CNTs.

This research aims to decrease the concentration of carbon nanotubes (CNTs) needed for enhancing the mechanical and thermal properties of acrylonitrile butadiene styrene (ABS)/CNTs nanocomposites using the recently introduced electromechanically dispersion technique (EMDT). EMDT efficiently disperses CNTs' agglomerations, preventing structural damage. Nanocomposites with various CNT concentrations were produced with EMDT, followed by injection molding to provide tensile strength, thermal conductivity, and impact resistance samples. Raman and differential scanning calorimetry (DSC) assessed CNT dispersion, revealing successful dispersion up to 0.2 wt% without structural damage. At this concentration, the tensile strength improved to 47.08 MPa, showing an increase of approximately 17.5%, and the thermal conductivity significantly increased to 0.29 W/mK, reflecting a 46% improvement. These results surpass those achieved by traditional dispersion methods, where 10 times the CNT concentration was required to reach similar enhancements. Higher injection temperatures and holding pressures improved CNT alignment and reduced entanglement, enhancing properties. However, no additional improvements were observed beyond 0.2 wt%. These findings highlight EMDT's potential in creating high‐performance nanocomposites with significantly lower CNT concentrations.Highlights Utilization of the novel EMDT dispersion method in nanocomposite preparation. Overcoming hindrances to commercializing CNT‐based polymeric nanocomposites. Reducing the required CNT concentration to attain significant properties. Improving tensile strength of ABS by ~17.5% with just 0.2 wt% of CNTs. Remarkable 48.4% increase in ABS thermal conductivity with just 0.2 wt% of CNTs.