Thermal transport enhancement of multi-walled carbon nanotubes/ high-density polyethylene composites

Multi-walled carbon nanotubes (MWCNTs) enhanced high-density polyethylene (HDPE) composites were prepared and their thermophysical properties were measured. The thermal diffusivity of the composites increases with the increase in the amount of MWCNTs. A thermal diffusivity of more than three times that of pure HDPE was obtained for 38 vol. % MWCNTs/HDPE composites. An equation based on an effective medium approach model was used to discuss the thermal diffusivity enhancement of MWCNTs/HDPE composites as a function of the volume fraction of MWCNTs. The results from this analysis can be a predictive guideline for further improvements in the thermal transport properties of MWCNTs/HDPE composites. Moreover, the intrinsic longitudinal thermal conductivity k_z of an individual MWCNT was deduced from the measured results on the MWCNTs/HDPE composites. PACS 67.55.Hc; 61.46.Fg; 66.30.Xj     

Evaluation of thermal and flame properties of HDPE-MWCNT-SiO2 nanocomposites

High-density polyethylene (HDPE) composites reinforced with multiwalled carbon nanotubes (MWCNTs) and nano-silicon dioxide (SiO₂) fillers were evaluated for flame retardancy and thermal properties for cable and wire applications. In this study, the filler percentages of MWCNT and nano-SiO₂ have varied from 0 to 5 wt% in HDPE composite with polyethylene-grafted glycidyl methacrylate compatibilizer and 3-aminopropyl triethoxy silane coupling agent. Addition of MWCNT’s and nano-SiO₂ to the HDPE composite is observed to enhance the limiting oxygen index and char formation. Cone calorimeter results also show a 53% reduction in the peak heat release rate of the HDPE composite with 5 wt% of MWCNT. The existence of synergism between the uniformly dispersed MWCNT and nano-SiO₂ has been verified using Finite Element Method (FEM)-based thermal simulations.     

Designing of multiwalled carbon nanotubes reinforced low density polyethylene nanocomposites for suppression of electromagnetic radiation

High aspect ratio multi-walled carbon nanotubes (MWCNTs) reinforced low density polyethylene (LDPE) composites were prepared by solvent casting followed by compression molding technique. Electromagnetic interference (EMI) shielding effectiveness (SE) of these composites was investigated in the frequency range of 12.4?C18 GHz (Ku-band) for the first time. The experimental results indicate that the EMI-SE of these composites is sensitive to the MWCNT loading. The average value of EMI-SE reaches 22.4 dB for 10 wt% MWCNT-LDPE composites, indicating the usefulness of this material for EMI shielding in the Ku-band. The main reason for improved SE has been attributed to significant improvement in the electrical conductivity of the composites by 20 orders of magnitude, i.e., from 10^?20 for pure LDPE to 0.63 S/cm for MWCNT-LDPE, which is three order of magnitude higher than the previous reports for MWCNT-LDPE composites. Differential scanning calorimetry of the MWCNT-LDPE composites showed around 37% improvement in the crystalline contents over pure LDPE samples which resulted into enhanced thermal stability of the composites. The thermal decomposition temperature of LDPE is shifted by 40 °C on addition of 5 wt% MWCNT. The studies therefore show that these composite can be used as light weight, thermally stable EMI shielding, and antistatic material.     

Improvement of the mechanical and rheological properties of HDPE/PET/MWCNT nanocomposites

High density polyethylene (HDPE)/poly (ethylene terephthalate) (PET) (90/10 wt.%) blends and HDPE/PET/multi-walled carbon nanotubes (MWCNTs) nanocomposites were prepared by melt mixing process, and the influence of MWCNTs on the mechanical and rheological properties of the nanocomposites was investigated. MWCNTs were added up to 5 wt.% in the HDPE/PET matrix. Transmission electron microscopy images reveal that the MWCNTs were homogeneously dispersed in the HDPE/PET matrix. Improvement of mechanical properties was observed by the addition of MWCNTs compared with HDPE/PET blends. Prominent increases in the complex viscosity and storage modulus of the nanocomposites were found with increasing MWCNT content.     

Electrical Properties of Isotactic Polypropylene/Multiwalled Carbon Nanotubes Composites Prepared by Vibration Injection Molding

To study the effect of vibration field on the electrical conductivity properties of nanocomposites, isotactic polypropylene (iPP)/multiwalled carbon nanotubes (MWCNT) composites were prepared by conventional injection molding and vibration injection molding. Results showed that the electrical conductivity of iPP/MWCNT composites was significantly promoted by vibration injection molding. Vibration injection molded samples had a percolation threshold of about 2.7 wt% compared with the threshold of about 4.5 wt% for conventional injection molded samples. The effects of test locations and vibration frequency on the electrical conductivity of composites were investigated. The samples exhibited an inhomogeneity along the injection direction. The electrical conductivity of the samples was different at different test locations and increased with increasing vibration frequency. Polarized light microscopy (PLM) results indicated that vibration injection molding can induce MWCNT aggregates to be stretched and oriented along the flow direction, which could form conductive networks and greatly enhance the electrical conductivity of iPP/MWCNT composites.     

Fabricating and improving properties of copper matrix nanocomposites by electroless copper-coated MWCNTs

In this study, copper (Cu) nanocomposites reinforced by coated multiwall carbon nanotubes (MWCNTs) have been fabricated with different weight fractions of MWCNT. In the first step, the as-received MWCNTs were coated with Cu using electroless deposition process. In the next step, combination of sonication and ball milling (with two milling time of 1.5 and 3 h) was used for preparing MWCNT/Cu composite powders. Finally, the disk-shaped specimens were sintered by hot-press sintering machine. Characterization of sintered nanocomposites revealed that increasing milling time led to improved mechanical properties, but higher defect density on the MWCNT sidewalls is obtained which is especially undesirable for electrical properties of nanocomposite. Our results indicated that simultaneous improvements of interface reactions and distribution uniformity of MWCNTs and Cu are key factors for obtaining enhanced mechanical properties. Accordingly, enhancement of up to ~150 and ~86 % in microhardness compared to pure Cu and 1 wt% as-received MWCNT/Cu was achieved by addition of 1 wt% Cu-coated MWCNT. On the contrary, existence of oxygen atoms in the Cu and coated MWCNT interface (from functional groups and deposited copper oxide) obstructs considerable improvement of electrical resistivity compared to as-received MWCNT/Cu nanocomposites.     

Investigation on Properties of Polypropylene/Multi-walled Carbon Nanotubes Nanocomposites Prepared by a Novel Eccentric Rotor Extruder Based on Elongational Rheology

The properties of polymer matrix composites are related not only to the chemical composition of the materials but also to the processing equipment used for their preparation which has a direct influence on the microstructure of the composites. In this paper polypropylene (PP)/multi-walled carbon nanotubes (MWCNTs) nanocomposites were prepared by melt blending through a self-developed, eccentric rotor extruder (ERE). The structure and elongational deformation mechanism of an ERE were described in detail. The morphological, rheological, thermal and mechanical properties of the resulting PP/MWCNTs nanocomposites were investigated. Scanning electron microscopy (SEM) and rheological analysis showed that the MWCNTs were well dispersed in the PP matrix. The thermal stability was investigated by thermogravimetric analysis (TGA) and indicated that the addition of MWCNTs could effectively improve the thermal stability of pure PP. The percentage of crystallinity and tensile strength of the composites were improved as a result of the heterogeneous nucleation effect of the MWCNTs in the PP matrix. The research results revealed that the enhancement of the properties of PP/MWCNTs composites could be attributed to a better dispersion of the MWCNTs in the matrix as compared to samples prepared by conventional extrusion.     

Electrical conductivity and electromagnetic interference shielding characteristics of multiwalled carbon nanotube filled polyacrylate composite films

Multiwalled carbon nanotubes (MWCNTs) were homogeneously dispersed in pure acrylic emulsion by ultrasonication to prepare MWCNT/polyacrylate composites applied on building interior wall for electromagnetic interference (EMI) shielding applications. The structure and surface morphology of the MWCNTs and MWCNT/polyacrylate composites were studied by field emission scanning microscopy (FESEM) and transmission electron microscopy (TEM). The electrical conductivity at room temperature and EMI shielding effectiveness (SE) of the composite films on concrete substrate with different MWCNT loadings were investigated and the measurement of EMI SE was carried out in two different frequency ranges of 100-1000 MHz (radio frequency range) and 8.2-12.4 GHz (X-band). The experimental results show that a low mass concentration of MWCNTs could achieve a high conductivity and the EMI SE of the MWCNT/polyacrylate composite films has a strong dependence on MWCNTs content in both two frequency ranges. The SE is higher in X-band than that in radio frequency range. For the composite films with 10 wt.% MWCNTs, the EMI SE of experiment agrees well with that of theoretical prediction in far field.     

Morphologies and Mechanical Properties of High-Density Polyethylene Induced by the Addition of Small Amounts of Both Low- and High-Molecular-Weight Polyolefin under Shear Stress Applied by Dynamic Packing Injection Molding

This paper focuses on the mechanical properties and crystal morphology of a self-reinforced high-density polyethylene 5000S (HDPE 5000S) by simultaneously blending with 9 wt% high-molecular-weight polyethylene (HMWPE) and 9 wt% low-molecular-weight polyethylene (LMWPE) (A9) under the shear stress field which was engendered by a self-made dynamic packing injection molding (DPIM) machine. The results of mechanical properties, differential scanning calorimetry, and scanning electron microscopy characterization were as follows: (1) The tensile strength of the dynamic samples increased to 112.1 MPa, 4.85 times as much as that of static packing injection molding (SPIM) samples (23.1 MPa), as a result of realizing polyethylene's self-enhancement; (2) Shish-kebab structure was found in the dynamic samples; (3) The crystallinity of the DPIM A9 sample reached 68.6%, on increase by 18.7% compared with that of the SPIM sample. The formation of the shish-kebab structure and enhancement of mechanical properties are explained.     

Morphological,Thermal, and Electrical Characterization of Syndiotactic Polypropylene/Multiwalled Carbon Nanotube Composites

In this work, syndiotactic polypropylene/multiwalled carbon nanotubes (MWCNT) nanocomposites, in various concentrations, were produced using melt mixing. The influence of the addition of MWCNT on the morphology, crystalline form, and the thermal and electrical properties of the polymer matrix was studied. To that aim, scanning electron microscopy, Raman spectroscopy, X-ray diffraction, differential scanning calorimetry, and dielectric relaxation spectroscopy were employed. Significant alterations of both the crystallization behavior and the thermal properties of the matrix were found on addition of the carbon nanotubes: conversion of the disordered crystalline form I to the ordered one, increase of the crystallization temperature and the degree of crystallinity, and decrease of the glass transition temperature and the heat capacity jump. Finally, the electrical percolation threshold was found between 2.5–3.0 wt.% MWCNT. For comparison purposes, the results of the system studied here are also correlated with the findings from a previous work on the isotactic polypropylene/MWCNT system.     

Assessment of the Microstructure and Mechanical Properties of Polycarbonate (PC)/Acrylonitrile Butadiene Rubber (NBR) Blends Reinforced with Multi-wall Carbon Nanotubes

Abstract

A series of polycarbonate (PC)/acrilonitrile butadiene rubber (NBR)/multi-wall carbon nanotube (MWCNT) nanocomposites were prepared via melt compounding in an internal mixer. The effect of the MWCNT content on the morphology and the thermal and mechanical properties of the prepared nanocomposites were studied. The morphologies of the samples were investigated by field-emission scanning electron microscopy (FESEM) and the thermal properties by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The tensile mechanical results of the nanocomposites showed a decrease in elongation at break with an increase of only 2?wt% of MWCNT content in the PC/NBR blends, and an increasing value in elastic modulus and tensile strength of the nanocomposites. The FESEM images showed that the MWCNTs had good affinity with the polymers and no compatibilizer was needed for making the nanocomposites. The DSC and TGA results showed an increase in thermal stability with addition of MWCNTs because of the more thermally stable carbon nanotubes particles which was uniformly dispersed within the nanocomposites.     

Addition of multiwalled carbon nanotube and graphene nanosheet in cobalt oxide film for enhancement of capacitance in electrochemical capacitors

In order to enhance the capacitance of electrochemical capacitors, multiwalled carbon nanotubes (MWCNTs) and graphene nanosheets (GNS) were added to cobalt oxide (Co₃O₄) paste. The composite film based on Co₃O₄/MWCNT/GNS (95:4:1 wt%) exhibited a capacitance of 294 F/g while the capacitance of Co₃O₄/MWCNT (95:5 wt%) and pure Co₃O₄ film is 205 and 163 F/g, respectively. The enhanced capacitance of Co₃O₄/MWCNT/GNS composite film was attributed to the electrochemical contributions of the Co₃O₄ nanoparticle attached to the GNS as well as their significantly increased specific surface areas by MWCNTs. Furthermore, the composite films showed faradaic redox capacitive behavior to double-layer capacitive behavior due to the different nanostructures of the composites.     

Synthesis of modified multi-walled carbon nanotube poly(benzimidazole-imide) composites: assessment of morphological and thermo-mechanical properties

A fully aromatic poly(benzimidazole-imide) (PBI) containing triazole side units and amine-modified multi-wall carbon nanotube (MWCNT)/PBI composites were fabricated via a polymerization process of monomer reactants and solution mixing with ultrasonication excitation. The polymer and composites were characterized by field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction. According to the microscopic characterizations, the MWCNTs homogeneously dispersed in the composites. The mechanical properties of the composite films were also measured by tensile test. The test results evidently indicated that the Young’s modulus increased by about 60.0% at 1 wt% CNT loading, and further modulus growth was observed at higher filler loading. The composite films hold preferable thermal stability the same as the pure PBI. The improvement of the mechanical and thermal properties was attributed to the incorporation of the surface modified CNTs. For CNT-reinforced polymer composites, strong interfacial adhesion and uniform dispersion of CNTs are more crucial factors for improving such properties.     

聚(2,5-二丁氧基)对苯乙炔/多壁碳纳米管复合材料的制备和性能研究

通过原位聚合法制备了聚（2,5-二丁氧基）对苯乙炔/多壁碳纳米管（PDBOPV/MWCNTs）复合材料.红外光谱和拉曼光谱证实了在MWCNTs表面的包覆层为PDBOPV.高分辨透射电子显微镜观察发现,PDBOPV/MWCNTs复合材料直径为35—45 nm,其中PDBOPV包覆层厚度约为15 nm.紫外—可见吸收光谱表明随着MWCNTs含量的增加,PDBOPV/MWCNTs的吸收发生红移且强度提高.荧光光谱研究表明随着MWCNTs含量的增加,PDBOPV/MWCNTs的最大发射波长发生蓝移且强度减小,MWCNTs与PDBOPV之间形成了光致电子转移体系,使得π电子离域程度增加,并且导致荧光量子效率降低.根据E_g与入射光子能量hν的关系,拟合了PDBOPV/MWCNTs薄膜的光学禁带宽度,发现随着MWCNTs的增加,E_g逐步减小.采用简并四波混频方法测试它们的三阶非线性极化率χ^（3）,结果发现随着MWCNTs含量的增加,PDBOPV/MWCNTs复合体的非线性光学响应逐渐增强,这说明PDBOPV与MWCNTs之间形成了分子间光致电子转移体系,产生了复杂的分子间π-π电子非线性运动. 关键词： 聚（2 5-二丁氧基）对苯乙炔 多壁碳纳米管 复合材料 光致发光     

Thermal and Mechanical Properties of Epoxy/Carbon Fiber Composites Reinforced with Multi-walled Carbon Nanotubes

Multi-scale hybrid composite laminates of epoxy/carbon fiber (CF) reinforced with multi-walled carbon nanotubes (MWCNTs) were fabricated in an autoclave. For laminate fabrication, 0.5 wt% of pristine MWCNTs or silane-functionalized MWNCTs (f-MWCNTs) were dispersed into a diglycidyl ether of bisphenol-A epoxy system and applied on the woven carbon fabric. The neat epoxy/CF composite and the MWCNTs-reinforced epoxy/CF hybrid composites were characterized by thermogravimetric analysis (TGA), thermomechanical analysis (TMA), tensile testing, and field emission scanning electron microscopy (FE-SEM). A significant improvement in initial decomposition temperature and glass transition temperature of epoxy/CF composite was observed when reinforced with 0.5 wt% of f-MWCNTs. The coefficient of thermal expansion (CTE), measured by TMA, diminished by 22% compared to the epoxy/CF composite, indicating an improvement in dimensional stability of the hybrid composite. No significant improvement in tensile properties of either MWCNTs/epoxy/CF composites was observed compared to those of the neat epoxy/CF composite.     

聚苯胺/碳纳米管复合体的制备及其三阶非线性光学性能研究

通过原位吸附-受限生长聚合法成功制备了聚苯胺/碳纳米管(PANI/MWCNT)复合体.红外光谱和拉曼光谱证实了在碳纳米管(MWCNT)表面的包覆层为聚苯胺(PANI).紫外—可见吸收光谱表明随着MWCNT含量的增加PANI的吸收发生红移且强度提高.扫描电子显微镜和透射电子显微镜观察发现，PANI/MWCNT复合体直径为40—70nm，其中PANI的包覆层厚度约为15—20nm.利用四波混频方法测试它们的三阶非线性光学系数，结果发现PANI/MWCNT复合体的三阶非线性光学系数比纯PANI大，这说明在MWC 关键词： 碳纳米管 聚苯胺 复合体 三阶非线性光学系数     

Carbon nanotubes as reinforcement of styrene-butadiene rubber

This study reports an easy technique to produce cured styrene-butadiene rubber (SBR)/multi-walled carbon nanotubes (MWCNT) composites with a sulphur/accelerator system at 150 °C. Significant improvement in Young's modulus and tensile strength were achieved by incorporating 0.66 wt% of filler without sacrificing SBR elastomer high elongation at break. A comparison with carbon black filled SBR was also made. Field emission scanning electron microscopy was used to investigate dispersion and fracture surfaces. Results indicated that the homogeneous dispersion of MWCNT throughout SBR matrix and strong interfacial adhesion between oxidized MWCNT and the matrix are responsible for the considerable enhancement of mechanical properties of the composite.     

Sono-assisted preparation of bio-nanocomposite for removal of Pb2+ ions: Study of morphology,thermal and wettability properties

Multi-walled carbon nanotubes (MWCNT) loaded poly(ethylene terephthalate) (PET) composites, with different CNT contents, were fabricated through an ultrasound assisted method as a fast and green way. Then, the obtained composites were fully characterized via FT-IR, UV–Vis, XRD, TGA, FE-SEM and TEM, etc. For this purpose, PET bottle was recycled and applied as matrix of nanocomposites (NC)s. Then, we dispersed the covalent functionalization of MWCNTs with a protein dispersant and obtained a powder of protein-functionalized CNTs. Bio-functionalized MWCNTs showed higher Pb²⁺ removal efficiency compared to MWCNT-COOH as ascertained via batch equilibrium adsorption experiments. Also, the results indicated the novel NCs presents a high affinity for Pb²⁺ heavy metal owing to the presence of several good sites. The contact angle results indicated that the addition of MWCNT-BSA increased significantly the contact angle compared to the pure PET. It was concluded that inflame retarding feature of NC was higher than pure polymer.     

Thermal and electrical conductivity of poly(l-lactide)/multiwalled carbon nanotube nanocomposites

Multiwalled carbon nanotubes (MWCNTs) are considered to be the ideal reinforcing agent for high-strength polymer composites, because of their fantastic mechanical strength, high electrical and thermal conductivity and high aspect ratio. Polymer/MWCNTs composites are easily molded, and the resulting shaped plastic articles have a perfect surface appearance compared with polymer composites made using usual carbon or glass fibers. Good interfacial adhesion between the MWCNTs and the polymer matrix is essential for efficient load transfer in the composite. The ultrahigh strength polymer composites demand the uniform dispersion of the MWCNTs in the polymer matrix without their aggregation and the good miscibility between MWCNT and polymer matrix. This approach can also be applied to biodegradable synthetic aliphatic polyesters such as poly(l-lactide) (PLLA), which has received a great deal of attention due to environmental concerns. In this study, PLLA was melt-compounded with MWCNTs. A high degree of dispersion of the MWCNTs in the composites was obtained by grafting PLLA onto the MWCNTs (PLLA-g-MWCNTs). After oxidizing the MWCNTs by treating them with strong acids, they were reacted with l-lactide to produce the PLLA-g-MWCNTs. The mechanical properties of the PLLA/PLLA-g-MWCNT composite were higher than those of the PLLA/MWCNT composite. The electrical conductivity of the composites was determined by measuring the volume resistivity, which is a value of the resistance expressed in a unit volume by two-probe method. The thermal diffusivity and heat capacity of composites was measured by laser flash method, and the effects of modification of the MWCNT in PLLA matrix are discussed.     

Tunable mechanical properties of MWCNT–glass fiber fabric reinforced epoxy composites by controlling MWCNTs dispersing conditions

A novel, simple and cost-effective method, which is capable of easily tailoring the dispersion of multi-walled carbon nanotubes (MWCNTs), was developed here to fabricate the MWCNT–glass fiber fabric (MWCNT–GFf) multiscale composites with tunable mechanical properties. MWCNTs were dispersed into the commercial GFfs through the combined effect of the ultrasound and amino silane (AS) firstly, followed by a resin infusion process. By tuning the ultrasonic power and AS concentration, it is possible to control the MWCNTs dispersion level and subsequently mechanical properties of resultant composite. Making use of optimal dispersion conditions, which involves the optimal combination of ultrasonic power and AS concentration, the interlaminar shear strength of MWCNT–GFf reinforced composites was dramatically increased by 40.5%, and the storage modulus in the glassy region and rubbery region was improved by 27.7% and 125.0%, respectively. The work demonstrates the great promise of this novel method toward practical, industrial application in manufacturing fiber-reinforced composites with superior mechanical properties.