Microstructure and mechanical property of multi-walled carbon nanotubes reinforced aluminum matrix composites fabricated by friction stir processing

Aluminum matrix composites reinforced by different contents of multi-walled carbon nanotubes (MWCNTs) were fabricated by friction stir processing (FSP). The microstructure of nano-composites and the interface between aluminum matrix and MWCNTs were examined using optical microscopy (OM) and transmission electron microscopy (TEM). It was indicated that MWCNTs were well dispersed in the aluminum matrix throughout the FSP. Tensile tests and microhardness measurement showed that, with the increase of MWCNT content, the tensile strength and microhardness of MWCNTs/Al composites gradually increased, but on the contrary, the elongation decreased. The maximum ultimate tensile strength reached up to 190.2 MPa when 6 vol.% MWCNTs were added, and this value was two times more of that of aluminum matrix. Appearances and fracture surface micrographs of failed composite samples indicated that the composites become more and more brittle with the increase of the MWCNT content.     

酸化处理多壁碳纳米管/氰酸酯树脂复合材料性能

采用酸化处理的多壁碳纳米管（MWCNTs）增强双酚A型氰酸酯-酚醛型氰酸酯（BCE-NCE）树脂。通过SEM、TEM对MWCNTs/BCE-NCE树脂复合材料微观结构进行表征,利用DSC、DMA和TG/DTA对MWCNTs/BCE-NCE树脂复合材料热性能进行研究,采用电子拉力机对MWCNTs/BCE-NCE树脂复合材料力学性能进行测试,采用谐振腔法对MWCNTs/BCE-NCE树脂复合材料介电性能进行测试。结果表明,混酸处理过的MWCNTs在BCE-NCE树脂基体中的分散效果较好。MWCNTs对BCE-NCE树脂热力学性能影响不大,当MWCNTs添加量为0.8wt%时,BCE-NCE树脂玻璃化转变温度（T_g）从298℃下降到285℃,但仍维持较高水平。当MWCNTs添加量为0.6wt%时,MWCNTs/BCE-NCE树脂复合材料冲击强度为11.40 kJ/m²,提高了40.7%。MWCNTs的加入增加了BCE-NCE树脂介电常数和介电损耗,当MWCNTs添加量为0.8wt%、频率为1 GHz时,MWCNTs/BCE-NCE树脂复合材料介电常数为5.1,介电损耗为0.032。因此,MWCNTs/BCE-NCE树脂复合材料未来可在耐高温复合材料和电子等行业应用。     

A comparative study on the electrical,thermal and mechanical properties of ethylene–octene copolymer based composites with carbon fillers

Conducting polymer composites (CPC) were prepared with an ethylene–octene copolymer (EOC) matrix and with either carbon fibers (CFs) or multiwall carbon nanotubes (MWCNTs) as fillers. Their electrical and thermal conductivities, mechanical properties and thermal stabilities were evaluated and compared. CF/EOC composites showed percolation behavior at a lower filler level (5 wt.%) than the MWCNT/EOC composites (10 wt.%) did. Alternating current (AC) conductivity and real part of permittivity (dielectric constant) of these composites were found to be frequency-dependent. Dimensions and electrical conductivities of individual fillers have a great influence on the conductivities of the composites. CF/EOC composites possessed higher conductivity than the MWCNT-composites at all concentrations, due to the higher length and diameter of the CF filler. Both electrical and thermal conductivities were observed to increase with increasing filler level. Tensile moduli and thermal stabilities of both (CF/EOC and MWCNT/EOC) composites increase with rising filler content. Improvements in conductivities and mechanical properties were achieved without any significant increase in the hardness of the composites; therefore, they can be potentially used in pressure/strain sensors. Thermoelectric behavior of the composites was also studied. Accordingly, CF and MWCNT fillers are versatile and playing also other roles in their composites than just being conducting fillers.     

Dispersions of carbon nanotubes/polyhedral oligomeric silsesquioxanes hybrids in polymer: the mechanical,electrical and EMI shielding properties

A hybrid was synthesized by grafting polyhedral oligomeric silsesquioxane (POSS) to multiwalled carbon nanotubes (MWCNTs). The MWCNT/polymer composites produced using silsesquioxane grafted MWCNTs as a filler had a high electromagnetic interference shielding effectiveness. Homogeneous dispersion of silsesquioxane grafted MWCNTs occurred throughout the polymer without any aggregation, while a pristine MWCNT aggregate that integrated several nanotube domains existed in the polymer matrix. A comparative study of the optical transmittance, electrical, and electromagnetic interference shielding properties of poly(l-lactide) (PLLA)/MWCNT composites based on pristine MWCNTs and silsesquioxane grafted MWCNTs was carried out. A high electromagnetic interference shielding effectiveness (15–16 dB) was obtained in the 36–50 GHz range at a relatively low filler loading (4 wt%) in the PLLA/silsesquioxane grafted MWCNT composite.     

Thermally reduced graphene oxide acting as a trap for multiwall carbon nanotubes in bi-filler epoxy composites

The effect of thermally reduced graphene oxide (TRGO) on the electrical percolation threshold of multi wall carbon nanotube (MWCNT)/epoxy cured composites is studied along with their combined rheological/electrical behavior in their suspension state. In contrast to MWCNT and carbon black (CB) based epoxy composites, there is no prominent percolation threshold for the bi-filler (TRGO–MWCNT/epoxy) composite. Furthermore, the electrical conductivity of the bi-filler composite is two orders of magnitude lower (∼1 × 10⁻⁵ S/m) than the pristine MWCNT/epoxy composites (∼1 × 10⁻³ S/m). This result is primarily due to the strong interaction between TRGO and MWCNTs. Optical micrographs of the suspension and scanning electron micrographs of the cured composites indicate trapping of MWCNTs onto TRGO sheets. A morphological model describing this interaction is presented.     

Structure and properties of highly oriented polyoxymethylene/multi-walled carbon nanotube composites produced by hot stretching

Highly-oriented polyoxymethylene (POM)/multi-walled carbon nanotube (MWCNT) composites were fabricated through solid hot stretching technology. With the draw ratio as high as 900%, the oriented composites exhibited much improved thermal conductivity and mechanical properties along the stretching direction compared with that of the isotropic samples before drawing. The thermal conductivity of the composite with 11.6 vol.% MWCNTs can reach as high as 1.2 W/m K after drawing. Microstructure observation demonstrated that the POM matrix had an ordered fibrillar bundle structure and MWCNTs in the composite tended to align parallel to the stretching direction. Wide-angle X-ray diffraction results showed that the crystal axis of the POM matrix was preferentially oriented perpendicular to the draw direction, while MWCNTs were preferentially oriented parallel to the draw direction. The strong interaction between the POM matrix and the MWCNTs hindered the orientation movement of molecules of POM, but induced the orientation movement of MWCNTs.     

Structure–property relationships in isotactic polypropylene/multi-walled carbon nanotubes nanocomposites

In this work, the influence of multi-walled carbon nanotubes (MWCNT) on electrical, thermal and mechanical properties of CNT reinforced isotactic polypropylene (iPP) nanocomposites is studied. The composites were obtained by diluting a masterbatch of 20 wt.% MWCNT with a low viscous iPP, using melt mixing. The morphology of the prepared samples was examined through SEM, Raman and XRD measurements. The effect of MWCNT addition on the thermal transitions of the iPP was investigated by differential scanning calorimetry (DSC) measurements. Significant changes are reported in the crystallization behavior of the matrix on addition of carbon nanotubes: increase of the degree of crystallinity, as well as appearance of a new crystallization peak (owing to trans-crystallinity). Dynamic mechanical analysis (DMA) studies revealed an enhancement of the storage modulus, in the glassy state, up to 86%. Furthermore, broadband dielectric relaxation spectroscopy (DRS) was employed to study the electrical and dielectric properties of the nanocomposites. The electrical percolation threshold was calculated 0.6–0.7 vol.% MWCNT from both dc conductivity and dielectric constant values. This value is lower than previous mentioned ones in literature in similar systems. In conclusion, this works provides a simple and quick way for the preparation of PP/MWCNT nanocomposites with low electrical percolation threshold and significantly enhanced mechanical properties.     

Synergetic effect of thermal conductive properties of epoxy composites containing functionalized multi-walled carbon nanotubes and aluminum nitride

This study investigates the thermal conductivity of epoxy composites containing two hybrid fillers which are multi-walled carbon nanotubes (MWCNTs) and aluminum nitride (AlN). To form a covalent bonds between the fillers and the epoxy resin, poly(glycidyl methacrylate) (PGMA) were grafted onto the surface of nano-sized MWCNTs via free radical polymerization and micro-sized AlN was modified by zirconate coupling agent. Results show that functionalized fillers improve thermal conductivity of epoxy composites, due to the good dispersion and interfacial adhesion, which is confirmed by scanning electron microscope. Furthermore, the hybrid fillers provide synergetic effect on heat conductive networks. The thermal conductivity of epoxy composites containing 25 vol.% modified AlN and 1 vol.% functionalized MWCNTs is 1.21 W/mK, comparable to that of epoxy composites containing 50 vol.% untreated AlN (1.25 W/mK), which can reduce the half quantity of AlN filler used.     

Tribological performance of carbon nanotube–graphene oxide hybrid/epoxy composites

An investigation is conducted on the effect of the hybrid of multi-wall carbon nanotubes (MWCNTs) and graphene oxide (GO) nanosheets on the tribological performance of epoxy composites at low GO weight fractions of 0.05–0.5 phr. The MWCNT amount is kept constant at 0.5 phr, which is typical for CNT/epoxy composites with enhanced mechanical properties. Friction and wear tests against smooth steel show that the introduction of 0.5 phr MWCNTs into the epoxy matrix increases the friction coefficient and decreases the specific wear rate. When testing the tribological performance of MWCNT/GO hybrids, it is shown that at a high GO amount of 0.5 phr, the friction coefficient is decreased below that of the neat matrix whereas the wear rate is increased above that of the neat matrix. At an optimal hybrid formulation, i.e., 0.5 phr MWCNTs and 0.1 phr GO, a further increase in the friction coefficient and a further reduction in the specific wear rate are observed. The specific wear rate is reduced by about 40% down to a factor of 11 relative to the neat epoxy when the GO content is 0.1 phr.     

Preparation,characterization and properties of polycaprolactone diol-functionalized multi-walled carbon nanotube/thermoplastic polyurethane composite

Multi-walled carbon nanotubes (MWCNTs) were chemically functionalized to prepare thermoplastic polyurethane (PU) composites with enhanced properties. In order to achieve a high compatibility of functionalized MWCNTs with the PU matrix, polycaprolactone diol (PCL), as one of PU’s monomers, was selectively grafted on the surface of MWCNTs (MWCNT–PCL), while carboxylic acid groups functionalized MWCNTs (MWCNT–COOH) and raw MWCNTs served as control. Both MWCNT–COOH and MWCNT–PCL improved the dispersion of MWCNTs in the PU matrix and interfacial bonding between them at 1 wt% loading fraction. The MWCNT–PCL/PU composite showed the greatest extent of improvement, where the tensile strength and modulus were 51.2% and 33.5% higher than those of pure PU respectively, without sacrificing the elongation at break. The considerable improvement in both mechanical properties and thermal stability of MWCNT–PCL/PU composite should result from the homogeneous dispersion of MWCNT–PCL in the PU matrix and strong interfacial bonding between them.     

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).     

Reducing resistivity of polyamide-6/multi-walled carbon nanotube composites by adding ultra-fine rubber particles on account of non-volume exclusion effect

The volume resistivity of polyamide-6(PA6)/multi-walled carbon nanotube (MWCNT) composites was found to be further reduced by adding a kind of ultra-fine rubber particle (URP) with average diameter of 150 nm due to non-volume exclusion effect. With the addition of 16 phr URP, the percolation threshold of PA6/MWCNT composites was reduced from 6 phr MWCNTs to 3 phr. Besides, at a constant loading of 4 phr MWCNTs, increase of URP loading led to two changes and a plateau for the volume resistivity of composites. The morphological observations of composites revealed that the decrease of volume resistivity was attributed to both homogenous dispersion and stretching of MWCNTs in PA6. The mechanism on better dispersion and stretching of MWCNTs with the help of URP was also given.     

Optimization of the mechanical properties of calcium phosphate/multi-walled carbon nanotubes/bovine serum albumin composites using response surface methodology

Response surface methodology (RSM) coupled with the central composite design (CCD) was used to optimize the mechanical properties of calcium phosphate cement/multi-walled carbon nanotubes/bovine serum albumin (CPC/MWCNTs/BSA) composites. In this study, CPC composites were reinforced by multi-walled carbon nanotubes (MWCNTs) and bovine serum albumin (BSA) in order to induce high mechanical properties in the CPC/MWCNTs/BSA system. The effect of various process parameters on the compressive strength of CPC/MWCNTs/BSA composites was studied using design of experiments (DOE). The process parameters studied were: wt.% of MWCNTs (0.2–0.5 wt.%), wt.% of BSA (5–15 wt.%) and type of MWCNTs (e.g. as-pristine MWCNT (MWCNT-AP), hydroxyl group functionalized MWCNT (MWCNT-OH) and carboxyl group functionalized MWCNT (MWCNT-COOH)). Based on the CCD, a quadratic model was obtained to correlate the process parameters to the compressive strength of CPC/MWCNTs/BSA composites. From the analysis of variance (ANOVA), the most significant factor affected on the experimental design response was identified. The predicted compressive strength after process optimization was found to agree well with the experimental value. The results revealed that at 0.5 wt.% of MWCNT-OH and 15 wt.% of BSA, the highest compressive strength of 14 MPa was obtained.     

多壁碳纳米管/聚偏氟乙烯高介电常数复合材料的制备与性能

为制备具有高介电常数的复合材料,采用注射成型法制备了原始多壁碳纳米管(P-MWCNTs)/聚偏氟乙烯(PVDF)复合材料和石墨化多壁碳纳米管(G-MWCNTs)/PVDF复合材料。然后,对P-MWCNTs和G-MWCNTs进行了Raman光谱表征,对MWCNTs/PVDF复合材料进行了断面形貌、力学性能和电学性能测试。结果表明:G-MWCNTs比P-MWCNTs具有更高的纯度和结晶度,两种不同的MWCNTs都能均匀分散在PVDF基体中,添加MWCNTs会显著影响PVDF的力学行为。MWCNTs/PVDF复合材料的介电性能随MWCNTs含量的增加而提高,与P-MWCNTs相比,G-MWCNTs有效降低了复合材料的渗流阈值。当频率为100 Hz时,纯PVDF的介电常数为7.0;当P-MWCNTs的含量为5wt%时,复合材料的介电常数为23.8;当G-MWCNTs的含量为5wt%时,复合材料的介电常数高达105.0。注射成型法制备的MWCNTs/PVDF复合材料仍保持相对较低的电导率,进而导致复合材料的能量损耗较低,对电荷存储应用具有重要意义。     

Effect of surface functionalization on mechanical properties and decomposition kinetics of high performance polyetherimide/MWCNT nano composites

In this investigation, Polyetherimide (PEI) reinforced with multi-walled carbon nanotube (MWCNT) using novel melt blending technique. Surface of MWCNTs are modified by acid treatment as well as by plasma treatment. PEI nano composites with 2 wt% treated MWCNT shows about 15% improvement in mechanical properties when compared to unfilled PEI. The thermal decomposition kinetics of PEI/MWCNT nano composites has been critically analyzed by using Coats – Redfern model. The increase in activation energy for thermal degradation by 699 kJ/mol for 2 wt% MWCNT implies improvement in the thermal properties of PEI. Studies under Fourier Transform Infrared Spectroscopy (FTIR) and Transmission Electron Microscopy (TEM) depict significant interfacial adhesion with uniform dispersion of MWCNT in polymer matrix due to surface functionalization. 0.5 wt% chemically modified MWCNT shows typical alignment of MWCNT. There is a significant improvement in mechanical properties and thermal properties for surface functionalized MWCNT reinforced.     

Rheological and mechanical properties of surface modified multi-walled carbon nanotube-filled PET composite

Poly(ethylene terephthalate) (PET)/multi-walled carbon nanotube (MWCNT) composites were prepared by in situ polymerization. To improve the dispersion of MWCNTs in PET matrix, the surface modified MWCNTs having acid groups (acid-MWCNT) and diamine groups (diamine-MWCNT) were used. The functional groups on the surface of modified MWCNTs were confirmed by infrared (IR) spectrometry. SEM analysis showed better dispersion of diamine-MWCNTs as compared to pristine-MWCNTs and acid-MWCNTs in the PET. The reaction between PET and diamine-MWCNTs was evidenced by the shifting of the G band to a higher frequency in Raman spectroscopy and an increase of the complex viscosity in rheological properties. The composites containing functionalized MWCNTs showed a large increase in the tensile strength and modulus. The PET/diamine-MWCNT composites showed maximum tensile strength and modulus increases by 350% and 290% at 0.5 and 2.0 wt%, respectively, as compared to pure PET.     

Effect of solid lubricant silicone powder on the fluidity and properties of polyarylene ether nitrile nanocomposite

Improving the processing performance of polymers is an eternal topic in the polymer field. As a processing aid, solid lubricants improve the shortcomings of liquid lubricants that are easy to migrate. In this work, silicone powder was introduced into polyarylene ether nitrile (PEN)/multi-walled carbon nanotubes (MWCNTs) composites as a solid lubricant to improve the flowability and processability. Firstly, the effects of silicone powder and MWCNTs on the mechanical properties, thermal properties, dielectric properties and rheological properties of the composites were investigated. The experimental results show that the fluidity of the composites is improved obviously by adding silicone powder. In addition, a comparative experiment was carried out. Compared with PEN/MWCNTs composites, PEN/silicone powder/MWCNTs composites have better processing properties and dielectric properties. The complex viscosity is 308.1 at 10² Hz and the dielectric constant is 1?×?10⁵ at 10³ Hz. Therefore, silicone powder is of great research value as a solid lubricant in the field of polymer-based functional materials.

     

Dielectric,mechanical and thermal properties of polymer/BaTiO3 composites for embedded capacitor

Barium titanate (BaTiO₃) filled polymethylmethacrylate (PMMA) composites were prepared using the simple solution method followed by hot pressing. The content of BaTiO₃ was varied from 0 to 65 vol.%. Scanning electron microscopy showed good dispersion and adhesion of BaTiO₃ with the PMMA matrix. The dielectric constant of the composites increased significantly. There was weak dispersion in the dielectric constant of the composites (up to 45 vol.%) with frequency between 100 Hz and 15 MHz. The dissipation factor of the composites increased from 0.021 for pure PMMA to 0.029 for 45 vol.% composites. However, 65 vol.% composite showed dispersion in dielectric constant with increasing frequency and higher dissipation factor. The Lichtenecker equation agreed well with the experimental data. The microhardness and the glass transition temperature of the composites increased approximately 4.7-fold and 42 °C, respectively, compared to pure PMMA. The CTE of the 65 vol.% composite is close to that of copper.     

Transparent,electrically conductive,and flexible films made from multiwalled carbon nanotube/epoxy composites

Optically transparent, conductive, and mechanically flexible epoxy thin films are produced in the present study. Two types of multiwalled carbon nanotubes (MWCNTs) with different aspect ratios are dispersed in epoxy resin through an ultrasonication process. The MWCNT content is varied during the preparation of the thin films. The light transmittance and electrical conductivity of the thin films are characterized. Results show that composites containing MWCNTs with a lower aspect ratio exhibit enhanced electrical conductivity compared to those with a higher aspect ratio. A sheet resistance as low as 100 Ω/sq with nearly 60% optical transparency in 550 nm is achieved with the addition of MWCNTs in epoxy. In summary, transparent, conductive, and flexible MWCNT/epoxy thin films are successfully produced, and the properties of such films are governed by the aspect ratio and content of MWCNTs.     

Effective load transfer by a chromium carbide nanostructure in a multi-walled carbon nanotube/copper matrix composite

Multi-walled carbon nanotube (MWCNT) reinforced copper (Cu) matrix composites, which exhibit chromium (Cr) carbide nanostructures at the MWCNT/Cu interface, were prepared through a carbide formation using CuCr alloy powder. The fully densified and oriented MWCNTs dispersed throughout the composites were prepared using spark plasma sintering (SPS) followed by hot extrusion. The tensile strengths of the MWCNT/CuCr composites increased with increasing MWCNTs content, while the tensile strength of MWCNT/Cu composite decreased from that of monolithic Cu. The enhanced tensile strength of the MWCNT/CuCr composites is a result of possible load-transfer mechanisms of the interfacial Cr carbide nanostructures. The multi-wall failure of MWCNTs observed in the fracture surface of the MWCNT/CuCr composites indicates an improvement in the load-bearing capacity of the MWCNTs. This result shows that the Cr carbide nanostructures effectively transferred the tensile load to the MWCNTs during fracture through carbide nanostructure formation in the MWCNT/Cu composite.