Fabrication and mechanical/conductive properties of multi-walled carbon nanotube (MWNT) reinforced carbon matrix composites

Multi-walled carbon nanotube (MWNT) reinforced carbon matrix (MWNT/C) composites have been explored using mesophase pitch as carbon matrix precursor in the present work. Results show that carbon nanotubes (CNTs)can enhance the mechanical properties of carbon matrix significantly. The maximal increment of the bending strength and stiffness of the composites, compared with the carbon matrix, are 147% and 400%, respectively. Whereas the highest in-plane thermal conductivity of the composites is 86 W m^− 1 K^− 1 which much lower than that of carbon matrix (253 W m^− 1 K^− 1).At the same time the electrical resistivity of the composites is much higher than that of matrix. It is implicated that CNTs seem to play the role of thermal/electrical barrier in the composites. FSEM micrograph of the fracture surface for the composites shows that the presence of CNTs restrains the crystallite growth of carbon matrix, which is one of factors that improve mechanical properties and decrease the conductive properties of the composites. The defects and curved shape of CNTs are also the affecting factors on the conductive properties of the composites.     

Reinforcing polyamide 1212 nanocomposites with aligned carbon nanofibers

In this study, the mechanical properties and structure orientation of pure polyamide 1212 (PA1212) were compared with those of PA1212–carbon nanofibers (CNFs) nanocomposites. The tensile strength of the composite containing 0.3 wt.% modified CNFs was improved from 328 MPa (pure PA1212) to 373 MPa after drawing. The reinforcing effect was investigated in terms of crystallization behavior, crystal morphology, alignment of CNFs, and crystal orientation degree. Spherulites developed into oriented crystals after drawing, and the CNFs aligned along the drawing direction. The heterogeneous nucleation effect of the aligned CNFs improved the crystal orientation degree, which produced the reinforcing effect. The oriented fibril structures with rigid nanofibers acting as nuclei reinforced the entire oriented crystals in the composites.     

Combination effect of carbon nanotubes with graphene on intumescent flame-retardant polypropylene nanocomposites

A novel polypropylene (PP) nanocomposite was fabricated by the incorporation of intumescent flame retardant (IFR), carbon nanotubes (CNTs) and graphene into the PP matrix. Results from TEM indicate that IFR, CNTs and exfoliated graphene nanosheets are dispersed finely in the PP matrix, which is supported by the XRD analysis results. Thermogravimetric (TGA) results show that the addition of IFR, CNTs and graphene improved the thermal stability and the char yields of PP. The PP/IFR/CNTs/RGO nanocomposites, filled with 18 wt% IFR, 1 wt% CNTs and 1 wt% graphene, achieve the limiting oxygen index value of 31.4% and UL-94 V0 grade. Cone calorimeter data reveal that combustion behavior, heat release rate peak (PHRR) and average specific extinction area (ASEA) of PP decrease substantially when combination effects of IFR, CNTs and graphene intervene. For the PP/IFR/CNTs/RGO nanocomposites, the PHRR exhibits an 83% reduction and the time of ignition is delayed 40 s compared with neat PP.     

A surfactant dispersed SWCNT-polystyrene composite characterized for electrical and mechanical properties

Single wall carbon nanotubes (SWCNTs) were dispersed in polystyrene (PS) at 0.1, 0.2, 0.3 and 1.0 wt.% (weight percent) concentrations using a surfactant assisted method. The resulting nanocomposites were characterized for their electrical conductivity, mechanical strength and fracture toughness properties. Results show a significant improvement in electrical conductivity with electrical percolation occurring by 0.2 wt.% SWCNT loading and the SWCNT-PS nanocomposite fully conductive at 1.0 wt.%. Three-point bend tests showed a decline in flexural strength and break strain with the addition of 0.1 wt.% SWCNTs. Improvements in the flexural modulus, strength and break strain with increasing SWCNT wt.% content followed The fracture toughness of the SWCNT-PS nanocomposites, in terms of the critical stress-intensity factor K_IC, was reduced relative to the neat material. From optical and high resolution scanning electron microscopy the presence of the carbon nanotubes is shown to have an adverse effect on the crazing mechanism in this PS material, resulting in a deterioration of the mechanical properties that depend on this mechanism.     

Preparation,morphology and properties of acid and amine modified multiwalled carbon nanotube/polyimide composite

The precursor of polyimide, polyamic acid, was prepared by reacting 4,4′-oxydianiline (ODA) with 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA). Unmodified, acid-modified and amine-modified multiwall carbon nanotubes (MWCNT) were separately added to the polyamic acid and heated to 300 °C to produce polyimide/carbon nanotube composite. Scanning electron microscopic (SEM) and transmission electron microscopic (TEM) microphotographs reveal that acid-modified MWCNT and amine-modified MWCNT were dispersed uniformly in the polyimide matrix. The effect of the acid and amine-modified MWCNTs on the surface and volume electrical resistivities of MWCNT/polyimide composites were investigated . The surface electrical resistivity of the nanocomposites decreased from 1.28 × 10¹⁵ Ω/cm² (neat polyimide) to 7.59 × 10⁶ Ω/cm² (6.98 wt% unmodified MWCNT content). Adding MWCNTs influenced the glass transition temperatures of the nanocomposites. Modified MWCNTs significance enhanced the mechanical properties of the nanocomposites. The tensile strength of the MWCNT/polyimide composite was increased from 102 MPa (neat polyimide) 134 MPa (6.98 wt% acid modified MWCNT/polyimide composites).     

Thermo-physical characterisation of epoxy resin reinforced by amino-functionalized carbon nanofibers

Epoxy/carbon nanofibers (CNFs) composites with different proportions of CNFs have been synthesised. In order to improve the CNFs dispersion into epoxy matrix, the nanofibers were functionalized with amino groups. The effect of the content and the functionalization of the nano-filler on the morphology of nanocomposite structure has been studied by optical and electron microscopies. It has been found that the CNFs dispersion is enhanced with the functionalization process up to nanofibers contents of 1 wt%. It has been also found that reached dispersion level markedly affects to the physical and thermo-dynamical mechanical properties of the epoxy nanocomposites.The addition of CNFs causes an important increase of the coefficient of thermal expansion and the glassy storage modulus of nanocomposites but the α-relaxation temperature decreases.     

Microstructure of carbon nanotubes/PET conductive composites fibers and their properties

Poly(ethylene terephthalate) (PET) resin has been compounded with carbon nanotubes (CNTs) using a twin-screw extruder. The composites of 4 wt% CNTs in PET had a volume electrical resistance of 10³ Ω cm, which was 12 orders lower than pure PET. The volume electrical conductivity of CNTs/PET composites with different CNTs containing followed a percolation scaling law of the form σ = κ(ρ − ρ_c)^t well. Scanning electron microscopy (SEM) micrograph showed that CNTs had been well dispersed in PET matrix. Optical microscopy micrograph showed that discontinuity of conductive phase existed in some segments of composite fiber. Rheological behavior of CNTs/PET composites showed that the viscosity of CNTs/PET composites containing high nanotube loadings exhibited a large decrease with increasing shear frequency. Crystallization behavior of CNTs/PET composites was studied by differential scanning calorimetry (DSC) and the nucleating effect of CNTs in the cooling crystallization process of PET was confirmed. Composite fiber was prepared using the conductive CNTs/PET composites and pure PET resin by composite spinning process. Furthermore, cloth was woven by the composite fiber and common terylene with the ratio 1:3. The cloth had excellent anti-static electricity property and its charge surface density was only 0.25 μC/m².     

Isolation of nanofibers from soybean source and their reinforcing capability on synthetic polymers

The focus of this work is to study nanofibers in three different polymers: polyvinyl alcohol (PVA), polypropylene (PP) and polyethylene (PE). The nanofibers were isolated from a soybean source by combining chemical and mechanical treatments. Isolated nanofibers were shown to have diameter between 50 and 100 nm and the length in micrometer scale which results in very high aspect ratio. The mechanical properties demonstrated an increase in tensile strength from 21 MPa of PVA/UNF5 (untreated-fiber (5 wt%) reinforced PVA) and 65 MPa of pure PVA to 103 MPa of PVA/SBN5 (nanofiber (5 wt%) reinforced PVA). The increased stiffness of PVA/SBN5 nanocomposites was also very promising; it was 6.2 GPa compared to 2.3 GPa of pure PVA and 1.5 GPa of PVA/UNF5. In solid phase melt-mixing, nanofiber was directly incorporated into the polymer matrix using a Brabender. The nanofiber addition significantly changed the stress–strain behavior of the composites: modulus and stress were increased with coated nanofibers by ethylene–acrylic oligomer emulsion as a dispersant; however, elongation was reduced. The dynamic mechanical analysis showed the addition of the soybean nanofiber (SBN) improved the thermal properties for PVA and how the addition of different contents of SBN influenced the tan δ peak and storage modulus of PVA.     

Carbon nanotubes rooted montmorillonite (CNT-MM) reinforced nanocomposite membrane for PEM fuel cells

Nafion based nanocomposite membranes containing montmorillonite-carbon nanotubes (a binary hybrid material) were produced to develop high performance polymer electrolyte fuel cells. Multi walled carbon nanotubes were grown over 20 and 25 wt% iron loaded montmorillonite catalysts by CVD using acetylene as the carbon precursor. Growth experiments were carried out at optimised conditions to obtain highly selective crystalline carbon nanotubes. X-ray diffraction spectra of the catalysts were recorded for the structural characterisation and definition of particle size. The carbon nanotubes obtained were examined by various physico chemical characterisation studies such as SEM, TEM, Raman spectroscopy and TG analyses to understand the morphology and crystallinity of the CNTs. The MM-CNT hybrid material with I_D/I_G ratio of Raman spectral band as 0.53 represents the high selectivity towards CNTs. Thus the hybrid material produced was considered as the best nanofiller to develop polymer nanocomposites. Nafion based nanocomposite membranes were prepared by adding MM-CNT as nanofiller by solution casting method. A better dispersion of MM-CNT into the Nafion matrix was observed and the addition of the MM-CNT improved the thermal stability of the Nafion membrane.     

Effect of amino functionalized MWCNT on the crosslink density,fracture toughness of epoxy and mechanical properties of carbon–epoxy composites

Amino functionalized multiwalled carbon nanotubes (A-MWCNTs) reinforced two phase (A-MWNT–epoxy) and three phase (A-MWCNTs–carbon fiber–epoxy) nanocomposites were fabricated with 0.25 wt%, 0.5 wt% and 1.0 wt% loadings of A-MWCNTs. It is observed that, A-MWCNTs can improve the crosslink density of epoxy significantly. Fracture toughness of epoxy matrix is found to increase up to an optimum crosslink density improvement, indicating the role of crosslink density in imparting toughness to epoxy apart from the crack deflection contributions of A-MWCNTs. In addition to that, this study infers that, tensile, flexural properties of the three phase composites are strongly influenced by the fracture toughness changes of the matrices. This study, thus proposes additional mechanisms of toughness enhancements for two phase and mechanical properties enhancements for three phase composites imparted by A-MWCNTs.     

Nylon 610/functionalized multiwalled carbon nanotubes composites by in situ interfacial polymerization

Nylon 610 (poly(hexamethylenesebacamide)) nanocomposites containing well dispersed multiwalled carbon nanotubes (MWCNT) were prepared using an in situ interfacial polymerization. Scanning electron microscopy showed that the MWCNT were well embedded and adhered to the nylon 610 matrix. The interfacial interaction of nylon 610/MWCNT on the grafted nylon 610 chains on the MWCNT was enhanced by improving the compatibility with nylon 610. This allowed a homogeneous dispersion of MWCNT in the nylon 610 matrix. Furthermore, the mechanical properties of nylon 610 were greatly improved by incorporating a small amount of MWCNT (0.1 wt.%). Because MWCNT are electrically conducting, the resulting electrical properties of the composites were approximately 5 orders of magnitude higher than pure nylon 610 matrix (from 10^− 17 S/cm to 10^− 12 S/cm). Overall, the results suggest that in situ polymerization is an ideal technique for producing a perfect dispersion of MWCNT in polymeric matrices.     

Preparation and characterization of carbon nanotube/polyetherimide nanocomposite films

Multi-walled carbon nanotube (MWCNT)/polyetherimide (PEI) nanocomposite films have been prepared by casting and imidization. A homogeneous dispersion of MWCNTs throughout the PEI matrix is observed by scanning electron microscopy of fracture surfaces, which shows not only a fine dispersion of MWCNTs but also strong interfacial adhesion with the matrix, as evidenced by the presence of many broken but strongly embedded carbon nanotubes (CNTs) in the matrix and by the absence of debonding of CNTs from the matrix. Differential scanning calorimetry and dynamic mechanical analysis show that the glass transition temperature of PEI increases by about 10 °C by the addition of 1 wt% MWCNTs. Mechanical testing shows that for the addition of 1 wt% MWCNTs, the elastic moduli of the nanocomposites are significantly improved by about 250% while the tensile strength is comparable to that of the matrix. This improvement is due to the strong interfacial interaction between the MWCNTs and the PEI matrix which favors stress transfer from the polymer to the CNTs.     

In situ preparation and mechanical properties of CNTs/MCMBs composites

By adding carbon nanotubes (CNTs) into medium temperature coal tar pitch, mesocarbon microbeads (MCMBs) were obtained via thermal condensation, then CNTs/MCMBs composites were in situ prepared using compression molding. The morphology, structure and mechanical properties of CNTs/MCMBs composites were characterized by optical microscope, digital camera, scanning electron microscope (SEM) and mechanical test machine. Results showed that CNTs were used as the nucleating agent and could inhibit the growth and coalescence of MCMBs. The optical textures of CNTs/MCMBs composites showed similar characteristics to the thermal condensation products from coal tar pitch with CNTs. The mass ratio of CNTs to coal tar pitch played an important role in the mechanical properties of CNTs/MCMBs composites. The density and bending strength of CNTs/MCMBs composite first increased and then decreased with the increase of the proportion of CNTs. When the proportion of CNTs was 5 wt%, the density of the composite reached the maximum (1.76 g/cm³). In addition, the bending strength of the composite reached the maximum (79.6 MPa) as adding 2 wt% CNTs into coal tar pitch.     

Fracture behaviour of α-Al2O3 ceramics reinforced with a mixture of single-wall and multi-wall carbon nanotubes

The extraordinary mechanical properties of single-wall carbon nanotubes (SWCNTs) and multi-wall carbon nanotubes (MWCNTs) have generated interest in incorporating them as toughening agents in ceramics. This work describes the fracture behaviour of an alumina (Al₂O₃) ceramic reinforced with a mixture of 0.05 wt% MWCNTs + 0.05 wt% SWCNTs. The CNT/Al₂O₃ nanocomposite was pressureless sintered in air using graphite powder as bed powder at 1520 °C for 1 h. The hardnesses and fracture toughnesses were lower than for pure Al₂O₃ and Al₂O₃ + 0.1 wt% SWCNTs and Al₂O₃ + 0.1 wt% MWCNTs. A predominantly transgranular fracture mode with a decrease in crack deflection and no pull-out was observed in the SWCNT + MWCNT–Al₂O₃ nanocomposite. MWCNTs had to the best reinforcing effect in Al₂O₃ nanocomposite.     

Improving the mechanical properties of epoxy using multiwalled carbon nanotubes functionalized by a novel plasma treatment

Achieving both uniform dispersion and good interfacial adhesion have been long-term challenges in optimizing the properties of carbon nanotube reinforced polymer nanocomposites. A novel and effective plasma method, which combines continuous and pulsed plasma modes in a nitrogen and hydrogen gas mixture (15% H₂), has been developed to better meet this need. It has yielded high levels of primary amines on the surface of multiwalled carbon nanotubes which improved their dispersion and interfacial bonding with an epoxy resin. By adding just 0.1 wt% of these nanotubes to Bisphenol F epoxy resin, the mechanical properties of the nanocomposites, from nano to macro, were significantly improved. Nanoindentation tests showed that the hardness and elastic modulus increased by 40% and 19%, respectively, using the functionalized nanotubes. Macro-mechanical properties from thermo-mechanical and flexural analysis were also enhanced, with a nearly 40% improvement in toughness.     

Strong and optically transparent biocomposites reinforced with cellulose nanofibers isolated from peanut shell

Cellulose nanofibers–reinforced PVA biocomposites were prepared from peanut shell by chemical–mechanical treatments and impregnation method. The composite films were optically transparent and flexible, showed high mechanical and thermal properties. FE-SEM images showed that the isolated fibrous fragments had highly uniform diameters in the range of 15–50 nm and formed fine network structure, which is a guarantee of the transparency of biocomposites. Compared to that of pure PVA resin, the modulus and tensile strength of prepared nanocomposites increased from 0.6 GPa to 6.0 GPa and from 31 MPa to 125 MPa respectively with the fiber content as high as 80 wt%, while the light transmission of the composite only decreased 7% at a 600 nm wavelength. Furthermore, the composites exhibited excellent thermal properties with CTE as low as 19.1 ppm/K. These favorable properties indicated the high reinforcing efficiency of the cellulose nanofibers isolated from peanut shell in PVA composites.     

Self-assembled multi-layered carbon nanofiber nanopaper for significantly improving electrical actuation of shape memory polymer nanocomposite

This study presents an effective approach to significantly improve the electrical properties of shape memory polymer (SMP) nanocomposites that show Joule heating triggered shape recovery. Carbon nanofibers (CNFs) were self-assembled to form multi-layered nanopaper to enhance the bonding and shape recovery behavior of SMP, respectively. It was found that both glass transition temperature (Tg) and electrical properties of the SMP nanocomposites have been improved by incorporating multi-layers of self-assembled nanopapers. The electrically actuated shape recovery behavior and the temperature profile during the actuation were monitored and characterized at a voltage of 30 V.     

Nanodiamond/poly (lactic acid) nanocomposites: Effect of nanodiamond on structure and properties of poly (lactic acid)

Nanodiamond (ND)/poly (lactic acid) (PLA) nanocomposites with potential for biological and biomedical applications were prepared by using melting compound methods. By means of transmission electron microscopy (TEM), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Thermogravimetric analyses (TGA), Dynamic mechanical analyses (DMA), Differential scanning calorimetry (DSC) and Tensile test, the ND/PLA nanocomposites were investigated, and thus the effect of ND on the structural, thermal and mechanical properties of polymer matrix was demonstrated for the first time. Experimental results showed that the mechanical properties and thermal stability of PLA matrix were significantly improved, as ND was incorporated into the PLA matrix. For example, the storage modulus (E′) of 3 wt% ND/PLA nanocomposites was 0.7 GPa at 130 °C which was 75% higher than that of neat PLA, and the initial thermal decomposition was delayed 10.1 °C for 1 wt% ND/PLA nanocomposites compared with the neat PLA. These improvements could be ascribed to the outstanding physical properties of ND, homogeneous dispersion of ND nanoclusters, unique ND bridge morphology and good adhesion between PLA matrix and ND in the ND/PLA nanocomposites.     

Effects of carbon nanotube alignment on electrical and mechanical properties of epoxy nanocomposites

This paper reports the alignment of multi-walled carbon nanotubes (MWCNTs) in an epoxy matrix as a result of DC electric fields applied during composite curing. Optical microscopy and polarized Raman spectroscopy are used to confirm the CNT alignment. The alignment of CNTs gives rise to much improved electrical conductivity, elastic modulus and quasi-static fracture toughness compared to those with CNTs of random orientation. An extraordinarily low electrical percolation threshold of about 0.0031 vol% is achieved when measured along the alignment, which is more than one order of magnitude lower than 0.034 vol% with random orientation or that measured perpendicular to the aligned CNTs. The examination of the fracture surfaces identifies pertinent toughening mechanisms in aligned CNT composites, namely crack tip deflection and CNT pullout. The significance of this paper is that the technique employed here can tailor the physical, mechanical and fracture properties of bulk nanocomposites even at a very low CNT concentration.     

Effect of dispersion conditions on the thermo-mechanical and toughness properties of multi walled carbon nanotubes-reinforced epoxy

In this work, multi wall carbon nanotubes (MWCNTs) dispersed in a polymer matrix have been used to enhance the thermo-mechanical and toughness properties of the resulting nanocomposites. Dynamic mechanical analysis (DMA), tensile tests and single edge notch 3-point bending tests were performed on unfilled, 0.5 and 1 wt.% carbon nanotube (CNT)-filled epoxy to identify the effect of loading on the aforementioned properties. The effect of the dispersion conditions has been thoroughly investigated with regard to the CNT content, the sonication time and the total sonication energy input. The CNT dispersion conditions were of key importance for both the thermo-mechanical and toughness properties of the modified systems. Sonication duration of 1 h was the most effective for the storage modulus and glass transition temperature (T_g) enhancement for both 0.5 and 1 wt.% CNT loadings. The significant increase of the storage modulus and T_g under specific sonication conditions was associated with the improved dispersion and interfacial bonding between the CNTs and the epoxy matrix. Sonication energy was the influencing parameter for the toughness properties. Best results were obtained for 2 h of sonication and 50% sonication amplitude. It was suggested that this level of sonication allowed appropriate dispersion of the CNTs to the epoxy matrices without destroying the CNT’s structure.