Electrically conductive carbon nanotube/polypropylene nanocomposite with improved mechanical properties

Conductive polymer nanocomposites based on carbon nanotubes (CNTs) have wide range of applications in the electronics and energy sectors. For many of these applications, such as the electromagnetic interference (EMI) shielding, high nanofiller loading is typically needed to achieve the desired properties. The high nanofiller concentration deteriorates the composite's tensile strength due to the increase in nanofiller aggregation. In this work, highly conductive CNT/polypropylene (PP) nanocomposite with improved tensile strength was prepared by melt mixing. The effects of CNT content on the processing behavior, microstructure, mechanical and electrical properties of the nanocomposite were investigated. Scanning electron microscopy was used to investigate the composite microstructure. Good level of CNT dispersion with remarkable adhesion at the CNT/PP interface was observed. Based on a theoretical model, the interfacial strength was estimated to be in the range of 36–58 MPa. As a result of this microstructure, significant enhancement in ultimate tensile strength was reported with the increase of CNT content. The tensile strength of the 20 wt.% CNT/PP nanocomposite was 80% higher than that of the unfilled PP. Moreover, and due to the good dispersion of CNT particles, an electrical percolation threshold concentration of 0.93 wt.% (0.5 vol.%) was obtained.     

Thermal conductivity of carbon nanotube reinforced aluminum composites: A multi-scale study using object oriented finite element method

In this study, object oriented finite element method (OOF) has been utilized to compute the thermal conductivity of plasma sprayed Al-12 wt.% Si containing 10 wt.% multiwall carbon nanotubes (CNTs). The computations have been made at micro- and macro-length scales which highlight the effect of CNT dispersion on thermal conductivity. Experimentally measured values at 50 °C indicate that CNT addition reduced the thermal conductivity of Al–Si matrix from 73 W m⁻¹ K⁻¹ to 25.4 W m⁻¹ K⁻¹ which is attributed to the presence of CNT clusters. OOF calculations at micro-length scale predicted an 81% increase in the conductivity of Al–Si matrix due to presence of well dispersed CNTs inside the matrix. At larger lengths scale, the decrease in the overall conductivity is related to the extremely low conductivity of CNT clusters. Thermal conductivity of CNT clusters could be up to three orders of magnitude lower than individual CNTs. OOF computed values match well with experimental results. OOF compute thermal conductivity of Al–CNT composite is also compared with theoretical two-phase models for CNT-composites at different length scales.     

Effects of diamond nanoparticles reinforcement into lead-free Sn–3.0Ag–0.5Cu solder pastes on microstructure and mechanical properties after reflow soldering process

This paper presents the effects of diamond nanoparticles reinforcement on lead-free SAC 305 solder paste after the reflow soldering process. Different diamond nanoparticles amounts (0.5, 1.5, and 2.5 wt.%) were mechanically mixed with SAC 305 to produce a new form of nanocomposite solder paste. The characteristics of the nanocomposite solder, such as melting point, morphology and thickness of the intermetallic compound (IMC), agglomeration of diamond nanoparticles, and hardness, were investigated. The experimental results revealed that the addition of diamond nanoparticles slightly decreases the melting point but significantly reduces the IMC thickness. The morphologies of the nano-reinforced solder paste showed the agglomeration of nanoparticles on the surface of the solder paste with increasing diamond nanoparticles percentage. The addition of 0.5 wt.% diamond nanoparticles was well embedded in the solder matrix after the reflow soldering process. The hardness of the nano-reinforced solder paste was evaluated via nanoindentation technique. The addition of 0.5 wt.% diamond nanoparticles improved the hardness of SAC 305 by 77.5%. Increasing the nanoparticles amount by 1.5 and 2.5 wt.% in SAC 305 enhanced the hardness of SAC 305–0.5 wt.% by 6.3% and 17.8%, respectively.     

Mechanical properties of carbon nanotube–alumina nanocomposites synthesized by chemical vapor deposition and spark plasma sintering

Carbon nanotubes–alumina (CNT–Al₂O₃) nanocomposites with variable CNT content were directly synthesized by chemical vapor deposition (CVD). The as-grown CNT–Al₂O₃ mixture was densified by spark plasma sintering (SPS) at 1150 and 1450 °C. Vickers hardness of 9.98 GPa and fracture toughness of 4.7 MPam^1/2 were obtained for 7.39 wt.% CNT–Al₂O₃ nanocomposite. The addition of CNTs gives rise to 8.4% increase in hardness and 21.1% increase in toughness over that of the pure Al₂O₃. The optimum amount of CNTs is considered to be able to significantly enhance the mechanical property of ceramics in composites.     

Synthesis of poly(ε-caprolactone)/hydroxyapatite nanocomposites using in-situ co-precipitation

Hybrid poly(ε-caprolactone) (PCL)/hydroxyapatite(HA) nanocomposites with various HA contents (0, 10, 20, 30 wt.%) were synthesized using an in-situ co-precipitation method. All nanocomposites prepared contained elongated HA nanocrystals dispersed uniformly in the PCL matrix without severe agglomeration. The tensile strength decreased from 13.5 ± 0.4 to 10.2 ± 0.3 MPa with increasing the HA content from 0 to 30 wt.%, whereas the elastic modulus increased from 85 ± 4.2 to 183 ± 6.6 MPa. In addition, the ALP activity was increased remarkably due to the presence of bioactive HA nanocrystals within the composites. The nanocomposite containing 30 wt.% HA showed a higher elastic modulus and ALP activity than the conventional PCL/HA composite with an initial HA content of 30 wt.%. This was attributed to the nanoscale hybridization of the HA nanocrystals without significant agglomeration.     

Effect of electroceramic particles on damping behaviour of aluminium hybrid composites produced by ultrasonic cavitation and mechanical stirring

In this study, electroceramics PBN and PLZT along with SiC were included in Al–3.96 wt.% Mg (A514.0) master alloy. Ultrasonic cavitation (UST) and mechanical stirring (MS) were employed to improve wettability and dispersion during casting. Two composite systems were produced: PBN system (5 wt.% PBN + 1 wt.% SiC and 15 wt.% PBN + 1 wt.% SiC) and the PLZT system (follows the same designation). The influence of fabrication method on the microstructures, particle distribution and wettability as well as electroceramic impact on dynamo-mechanical properties of prepared composites were investigated. Optical microscope (OM) and scanning electron microscope (SEM) results indicate that the processing technique was effective as it promoted wettability and homogeneous dispersion of particles throughout the Al matrix. Dynamic mechanical analysis (DMA) study of the composites demonstrated that the addition of the functional particles to the Al alloy matrix improved damping capacity (Tan δ) at 200 °C. The composites exhibited an increase in Tan δ of 24.3 ± 0.3% and 91.4 ± 0.2% for 5 and 15 wt.% PBN + 1 wt.% SiC and an increase of 19.7 ± 0.5% and 42.5 ± 0.3% for 5 and 15 wt.% PLZT + 1 wt.% SiC, respectively, when compared to the aluminium alloy matrix.     

An investigation of the synthesis,consolidation and mechanical behaviour of Al 6061 nanocomposites reinforced by TiC via mechanical alloying

Nanostructured Al 6061–x wt.% TiC (x = 0.5, 1.0, 1.5 and 2.0 wt.%) composites were synthesised by mechanical alloying with a milling time of 30 h. The milled powders were consolidated by cold uniaxial compaction followed by sintering at various temperatures (723, 798 and 873 K). The uniform distribution and dispersion of TiC particles in the Al 6061 matrix was confirmed by characterising these nanocomposite powders by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), differential thermal analysis (DTA) and transmission electron microscopy (TEM). The mechanical properties, specifically the green compressive strength and hardness, were tested. A maximum hardness of 1180 MPa was obtained for the Al 6061–2 wt.% TiC nanocomposite sintered at 873 K, which was approximately four times higher than that of the Al 6061 microcrystalline material. A maximum green compressive strength of 233 MPa was obtained when 2 wt.% TiC was added. The effect of reinforcement on the densification was studied and reported in terms of the relative density, sinterability, green compressive strength, compressibility and Vickers hardness of the nanocomposites. The compressibility curves of the developed nanocomposite powders were also plotted and investigated using the Heckel, Panelli and Ambrosio Filho and Ge equations.     

Evaluation of the flexural properties and bioactivity of bioresorbable PLLA/PBSL/CNT and PLLA/PBSL/TiO2 nanocomposites

Bioresorbable nanocomposites made from PLLA/PBSL blended with varying contents of carbon nanotubes (CNTs) and titanium dioxide (TiO₂) nanotubes were prepared through melt compounding followed by compression molding. The resulting flexural properties were investigated by flexural test and the bioactive behavior was assessed by FESEM and EDX. A higher flexural modulus value was obtained with the addition of nanofillers. The formation of a bone-like apatite layer was observed on the surface of the nanocomposite containing TiO₂ nanotubes after soaking in simulated body fluid (SBF) for 7 days. An increase in the water uptake of the PLLA/PBSL/TiO₂ nanocomposite occurred with increased filler loading. The nanocomposite containing CNT exhibited an increasing trend of water absorption similar to the PLLA/PBSL blend. With prolonged immersion in SBF, the pH value of the SBF reduced slightly and weight loss of the samples increased.     

Effect of different carbon nano-fillers on rheological properties and lap shear strength of epoxy adhesive joints

In this work, the rheological properties, thermal stability and the lap shear strength of epoxy adhesive joints reinforced with different carbon nano-fillers such as multi-walled carbon nanotubes (CNT), graphene nanoplatelets (GNP) and single-walled carbon nanohorns (CNH) have been studied. The nano-fillers were dispersed homogeneously using Brabender® Plasti-Corder®. The epoxy pre-polymer with and without the nano-fillers exhibited shear thinning behavior. The nano-filler epoxy mixtures exhibited a viscoplastic behavior which was analyzed using Casson’s model. Thermo-gravimetric analysis indicated an increase in the thermal stability of the epoxy with the addition of carbon nano-fillers. Carbon nano-fillers resulted in increased lap shear strength having high Weibull modulus. The joint strength increased by 53%, 49% and 46% with the addition of 1 wt.% CNT, 0.5 wt.% GNP and 0.5 wt.% CNH, respectively. The strength of the joints having high filler content (>1 wt.%) was limited by mixed mode type of failure.     

Effect of ionic liquid on the structure and tribological properties of polycarbonate–zinc oxide nanodispersion

Room-temperature ionic liquid (IL) 1-hexyl-3-methylimidazolium hexafluorophosphate has been added to PC + 0.5 wt.%ZnO nanocomposite in a 1.5 wt.% proportion to obtain PC + 0.5%ZnO + 1.5%IL. The new PC/ZnO/IL nanocomposite shows a 80% friction reduction and a wear reduction of nearly two orders of magnitude with respect to PC + 0.5%ZnO. The influence of IL on the size, morphology and distribution of ZnO nanoparticles in the PC matrix is discussed on the basis of scanning (SEM) and transmission (TEM) electronic microscopic observations and energy dispersive X-ray (EDX) analysis.     

Effects of Ca addition on as-cast microstructure and mechanical properties of Mg–3Ce–1.2Mn–1Zn (wt.%) magnesium alloy

The effects of Ca addition on the as-cast microstructure and mechanical properties of the Mg–3Ce–1.2Mn–1Zn (wt.%) alloy were investigated by using optical and electron microscopes, differential scanning calorimetry (DSC) analysis, and tensile and creep tests. The results indicate that the additions of 0.3–0.9 wt.%Ca to the Mg–3Ce–1.2Mn–1Zn alloy do not cause an obvious change in the morphology and distribution for the Mg₁₂Ce phase in the alloy. However, the grains and secondary dendrite arm spacings of the Ca-containing alloys are refined, and an increase in Ca amount from 0.3 wt.% to 0.9 wt.% causes the grain size and secondary dendrite arm spacings to gradually decrease, respectively. In addition, the additions of 0.3–0.9 wt.%Ca to the Mg–3Ce–1.2Mn–1Zn alloy can effectively improve the as-cast tensile and creep properties of the alloy, and an increase in Ca amount from 0.3 wt.% to 0.9 wt.% causes the as-cast tensile and creep properties to gradually increase, respectively.     

Fabrication of microwave exfoliated graphite oxide reinforced thermoplastic polyurethane nanocomposites: Effects of filler on morphology,mechanical, thermal and conductive properties

Different formulations of microwave-exfoliated graphite oxide (MEGO) based thermoplastic polyurethane (TPU) nanocomposites were successfully prepared via melt blending followed by injection molding. The spectroscopic study indicated that a strong interfacial interaction had developed between the MEGO and the TPU matrix. The microscopic observations showed that the MEGO layers were homogeneously dispersed throughout the TPU matrix. Thermal analysis indicated that the glass transition temperatures (T_g) of the nanocomposites increased with increasing MEGO content and their thermal stability improved in comparison with pure TPU matrix. The mechanical properties of nanocomposites improved substantially by the incorporation of MEGO into the TPU matrix. Electrical conductivity test indicated that a conductivity of 10⁻⁴ S cm⁻¹ was achieved in the nanocomposite containing only 4.0 wt.% of MEGO.     

Effect of 10Ce-TZP/Al2O3 nanocomposite particle amount and sintering temperature on the microstructure and mechanical properties of Al/(10Ce-TZP/Al2O3) nanocomposites

A zirconia/alumina nanocomposite stabilized with cerium oxide (Ce-TZP/Al₂O₃ nanocomposite) can be a good substitute as reinforcement in metal matrix composites. In the present study, the effect of the amount of 10Ce-TZP/Al₂O₃ particles on the microstructure and properties of Al/(10Ce-TZP/Al₂O₃) nanocomposites was investigated. For this purpose, aluminum powders with average size of 30 μm were ball-milled with 10Ce-TZP/Al₂O₃ nanocomposite powders (synthesized by aqueous combustion) in varying amounts of 1, 3, 5, 7, and 10 wt.%. Cylindrical-shape samples were prepared by pressing the powders at 600 MPa for 60 min while heating at 400–450 °C. The specimens were then characterized by scanning and transmission electron microscopy (SEM and TEM) in addition to different physical and mechanical testing methods in order to establish the optimal processing conditions. The highest compression strength was obtained in the composite with 7 wt.% (10Ce-TZP/Al₂O₃) sintered at 450 °C.     

Microstructure development and tensile mechanical properties of Mg–Zn–RE–Zr magnesium alloy

The Mg–5.3 wt.%Zn–1.13 wt.%Nd–0.51 wt.%La–0.28 wt.%Pr–0.79 wt.%Zr alloy prepared by direct chill casting is subjected to hot extrusion. The effects of extrusion ratio and temperature on microstructure and tensile mechanical properties have been studied. The results indicate coarse grains of as-cast alloys are refined with extrusion ratio increasing from 0 to 9. The eutectic constituents are elongated along extrusion direction. However, further increase of extrusion ratio has a little influence on grain refinement and the improvement of mechanical properties of the alloy. Dynamic recrystallisation is the main mechanism of grain refinement during hot extrusion. Raising extrusion temperature results in grain coarsening. Grain shape becomes more equiaxed-like with raising extrusion temperature. At the same time, mechanical properties decrease with the increase of extrusion temperature.     

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.     

Fabrication of conductive porous alumina (CPA) structurally modified with carbon nanotubes (CNT)

A novel binary porous composite nano-carbon networks (NCNs)/alumina, which is denoted as electrically conductive porous alumina (CPA), was structurally modified by carbon nanotubes (CNT) pre-treated with mixed concentrated acids at 60 °C for 6 h in this study. This conductive ceramics (CCs) was fabricated by combination of gelcasting and high temperature reductive sintering (HTRS) in novel atmosphere. CNT pre-treatment leading to the increased hydrophilicity makes it possible to make uniformly dispersed CNT/alumina slurry. And by HTRS in Ar at 1700 °C for 2 h, well-gelled polymer net-paths in green body prepared by gelcasting technology were totally converted to nano-carbon networks (NCNs) without destruction of CNT. NCN with graphitic crystal structure was evaluated by Raman spectroscopy in sintered ceramic body. Moreover, comparing with as-received CNT, the decreased surface defect of detected composite also supported the further graphitization of CNT via HTRS in Ar instead of burning out. With the aid of field-emission scanning electronic microscopy (FE-SEM) observation, the increased alumina grains in sintered ceramic body CNT/NCN/alumina was valid. Moreover, it was demonstrated that there were three components in this composite, which is carbon filler with two different forms (CNT and NCN) and alumina matrix. And these three components CNT covered with Al₂O₃ particles (Al₂O₃/CNT), NCN and alumina grains (alumina) co-exist in four different situations as follows: (a) Al₂O₃/CNT–alumina co-junction, (b) Al₂O₃/CNT–NCN co-junction, (c) Al₂O₃/CNT–alumina–NCN and (d) Al₂O₃/CNT mesh between alumina boundaries. Furthermore, by comparing with binary composite NCN/alumina (CPA), the increased flexural strength of ternary composite CNT/NCN/alumina (CNT/CPA) up to 38 MPa was attributed to the reinforcement CNT acting as elastic bridge in composite.     

Porous poly(vinyl alcohol)/sepiolite bone scaffolds: Preparation,structure and mechanical properties

Porous poly(vinyl alcohol) (PVA)/sepiolite nanocomposite scaffolds containing 0–10 wt.% sepiolite were prepared by freeze-drying and thermally crosslinked with poly(arylic acid). The microstructure of the obtained scaffolds was characterised by scanning electron microscopy and micro-computed tomography, which showed a ribbon and ladder like interconnected structure. The incorporation of sepiolite increased the mean pore size and porosity of the PVA scaffold as well as the degree of anisotropy due to its fibrous structure. The tensile strength, modulus and energy at break of the PVA solid material that constructed the scaffold were found to improve with additions of sepiolite by up to 104%, 331% and 22% for 6 wt.% clay. Such enhancements were attributed to the strong interactions between the PVA and sepiolite, the good dispersion of sepiolite nanofibres in the matrix and the intrinsic properties of the nanofibres. However, the tensile properties of the PVA scaffold deteriorated in the presence of sepiolite because of the higher porosity, pore size and degree of anisotropy. The PVA/sepiolite nanocomposite scaffold containing 6 wt.% sepiolite was characterised by an interconnected structure, a porosity of 89.5% and a mean pore size of 79 μm and exhibited a tensile strength of 0.44 MPa and modulus of 14.9 MPa, which demonstrates potential for this type of materials to be further developed as bone scaffolds.     

Effects of indium addition on properties and wettability of Sn–0.7Cu–0.2Ni lead-free solders

This paper reports the investigation on indium addition into Sn–0.7Cu–0.2Ni lead-free solder to improve its various performances. The effects of indium addition on melting temperature, coefficient of thermal expansion (CTE), wettability, corrosion resistance and hardness of the solder alloys were studied. The results showed that when the addition of indium was ⩽0.3 wt.%, the change in melting temperature of Sn–0.7Cu–0.2Ni–xIn solders was negligible, but the melting range of the solder alloy increased. The CTE and spreading area of Sn–0.7Cu–0.2Ni–xIn solders on copper both increased with the addition of indium. An optimal CTE was 17.5 × 10⁻⁶/°C by adding 0.3 wt.% indium. At this concentration, the spreading area of solder on copper was about 15.6% larger than that of Sn–0.7Cu–0.2Ni indium-free solder. The corrosion resistance also increased with the addition of indium increasing, and the corrosion rate of Sn–0.7Cu–0.2Ni–0.3In solder was reduced by 32.8% compared with Sn–0.7Cu–0.2Ni alloy after 14 days in 5% hydrochloric acid solution at room temperature. However, a decrease of 11.7% in hardness of the solder was found when 0.3 wt.% indium was added.     

Effect of boron addition on the cavitation erosion resistance of Fe-based hardfacing alloy

The cavitation erosion behavior of Fe–Cr–C–Si–xB (x = 0, 0.3 and 0.6 wt.%) alloys were investigated up to 50 h by using 20 kHz vibratory cavitation erosion test equipment. The boron-added alloys showed the improved cavitation erosion resistance compared to the boron-free alloy. This improvement was attributed to that the boron addition enhanced the grain boundary strength and refined the grain size of the matrix. However, the cavitation erosion rate of the 0.6 wt.% boron specimen was higher than that of the 0.3 wt.% boron specimen. The higher erosion rate of the 0.6 wt.% boron was due to the larger carbide volume in the matrix.     

Advanced multifunctional properties of aligned carbon nanotube-epoxy thin film composites

Carbon nanotube (CNT)/epoxy composite films were successfully developed by a combination of layer-by-layer and vacuum-assisted resin transfer molding methods using directly chemical vapor deposition (CVD)-spun CNT plies. CNT fractions in the composite films were found to be dramatically enhanced as the number of CNT plies increased. The as-prepared CNT/epoxy composite films with 24.4 wt.% CNTs exhibited ~ 10 and ~ 5 times enhancements in their strength and Young's modulus, respectively, and high toughness of up to 6.39 × 10³ kJ/m³. Electrical conductivity reached 252.8 S/cm for the 20-ply CNT/epoxy films, which was 20 times higher over those of the CNT/epoxy composites obtained by conventional dispersion methods. This work proposed a route to fabricate high-CNT-fraction CNT/epoxy composites on a large scale. The high toughness of these CNT/epoxy composite films also makes them promising candidates as protective materials.