Significant enhancement of electrical and thermal conductivities of polyethylene carbon nanotube composites by the addition of a low amount of silver nanoparticles

Electrically and thermally conductive high‐density polyethylene composites filled with hybrid fillers, multiwall carbon nanotubes (MWCNTs) and silver nanoparticles (Ag‐NPs), have been prepared in the melt state. The investigation of their electrical and thermal conductivities while comparing with high‐density polyethylene/MWCNT binary composites shows that the addition of only 3 vol% of Ag‐NPs does not reduce the electrical percolation threshold (P_c) that remains as low as 0.40 vol% of MWCNTs but leads to an increase in the maximum dc electrical conductivity of PE/MWCNT composites by two orders of magnitudes. Moreover, the association of both Ag‐NPs and carbon nanotube particles improved our composite's thermal conductivity. Copyright © 2014 John Wiley & Sons, Ltd.     

Positive Temperature Coefficient Characteristics of Multi-walled Carbon Nanotube Filled Polyvinylidene Fluoride Nanocomposites

Composites of polyvinylidene fluoride (PVDF) and multi-wall carbon nanotubes (MWNT) were prepared by a melt mixing process. Temperature dependence of electrical properties of the nanocomposites was investigated for composites containing different amounts of MWNT. An obvious positive temperature coefficient was observed. It was found that resistivity of the composites was decreased with increasing MWNT content and the electrical percolation threshold was formed at 3 wt% MWNT, which were caused by the formation of conductive chains in the composites. The mechanism of the positive temperature coefficient behavior of the nanocomposites is discussed. The rheological results showed that the materials experience a fluid–solid transition at the composition of 2 wt%, beyond which a continuous MWNT network forms throughout the matrix leading to a percolated network structure, which further indictes the nanotubes were dispersed uniformaly, in the PVDF matrix.     

Filler network structure in graphene nanoplatelet (GNP)-filled polymethyl methacrylate (PMMA) composites: From thermorheology to electrically and thermally conductive properties

In this work, graphene nanoplatelet (GNP) filled polymethyl methacrylate (PMMA) composites were prepared using solution method via a specially designed route and relatively high thermal conductivities of the composites were achieved at a low GNP loading. The effect of GNP content on rheological behavior, thermal and electrical conductivity of the composites was intensively investigated. Thermorheological complexity was displayed at elevated GNP loading, and the rheological percolation threshold of GNP in PMMA decreased from 7.96 wt% at 220 °C to 4.02 wt% at 260 °C according to Winter-Chambon method, suggesting that GNP was more likely to form a seepage network at higher temperature. The DMTA results showed that the increase in moduli of the composites should be ascribed to the formation of the GNP-GNP network structure. The electrical conductivity of the composites underwent a sudden jump by seven orders of magnitude, which also indicated the formation of a GNP conductive pathway in the matrix with an electrical percolation threshold of 2–4 wt%. The results of transient temperature measurement were in good consistent with the thermal conductivity versus GNP loading, which was compared with various thermal conduction models with a modified Agari model presenting an acceptable evaluation of the dispersion status of GNP in the matrix. The experimental electrical and thermal conductivities as a function of GNP content could well be interpreted by the filler network structure as observed in morphological studies.     

Multi walled carbon nanotubes induced viscoelastic response of polypropylene copolymer nanocomposites: Effect of filler loading on rheological percolation

Polypropylene random copolymer nanocomposites having 0.2–7.0 vol% multi-walled carbon nanotubes (MWCNTs) were prepared via melt processing. Transmission electron microscopy (TEM) was employed to determine the nano scale dispersion of carbon nanotubes. Linear viscoelastic behavior of these nanocomposites was investigated using parallel plate rheometry. Incorporation of carbon nanotubes in the polymer matrix resulted in higher complex viscosity (η*), storage (G′) and loss modulus (G″) as compared to neat polymer, especially in the low-frequency region, suggesting a change from liquid to solid-like behavior in the nanocomposites. By plotting storage modulus vs. carbon nanotube loading and fitting with a power law function, the rheological percolation threshold in these nanocomposites was observed at a loading of ∼0.27 vol% of MWCNTs. However, electrical percolation threshold was reported at ∼0.19 vol% of MWCNTs loading. The difference in the percolation thresholds is understood in terms of nanotube connectivity with nanotubes and polymer chain required for electrical conductivity and rheological percolation.     

纤维状填料/HDPE复合体系的导电渗流与流变渗流行为的关系

研究了纤维状导电材料不锈钢纤维(SSF)填充高密度聚乙烯(HDPE)导电复合体系的导电渗流与流变渗流行为之间的关系,并与颗粒状导电颗粒炭黑(CB)/HDPE导电复合体系进行了比较.发现当SSF含量极低(0.3vol%)时,SSF/HDPE体系即发生导电渗流现象,且导电渗流转变区域极窄;而仅当SSF含量达到4.8vol%时,该复合体系才表现出流变渗流现象,这一结果与CB/HDPE体系及纳米级导电纤维填充体系截然不同.此外,通过正温度系数效应的研究发现SSF形成的导电通路稳定性高于CB/HDPE体系.我们认为,SSF/HDPE体系呈现的这些特点均与SSF较大的直径及长径比且其导电通路及流变渗流网络的形成机理不同有关.     

多壁碳纳米管对聚甲醛性能的影响

将多壁碳纳米管(MWCNTs)和聚甲醛(POM)在转矩流变仪中熔融混合得到POM/MWCNT复合材料.研究了复合材料的形态,导热性能,导电性能,流变性能和结晶性能.结果表明,MWCNTs在没有经过处理的情况下能够均匀地分散在POM基体中;当向POM中添加1.0 wt%含量MWCNTs时,复合材料的导热系数上升到0.5289 W/(K m),比纯POM的导热系数0.198 W/(K m)提高1.5倍,通过有效介质方法(EMA)验证了体系导热系数提高幅度不大的原因是MWCNTs与POM之间形成了很高的界面热阻;当MWCNTs的含量为1.0 wt%时,体系产生了导电逾渗效应,逾渗值在0.5 wt%~1.0 wt%之间;MWCNTs对POM有显著的成核作用,当向POM中添加0.5 wt%含量的MWCNTs时,POM的结晶温度提高6℃左右,但当MWCNTs的添加量进一步增加时,结晶温度几乎不再变化,成核效果呈现"饱和"状态.另外,材料的复数黏度,储能模量和损耗模量随MWCNTs含量的增加而增加.     

Isotactic polypropylene/carbon nanotube composites prepared by latex technology: Electrical conductivity study

Several series of nanocomposites were prepared using a latex-based process, the main step of which consisted of mixing an aqueous suspension of exfoliated carbon nanotubes (CNTs) and a polymer latex. In the present work, a systematic study on the electrical properties of fully amorphous (polystyrene - PS) as well as semi-crystalline (isotactic polypropylene - iPP) nanocomposites containing either single-wall (SWCNTs) or multi-wall carbon nanotubes (MWCNTs) has been conducted. Percolation thresholds as low as 0.05 wt.% or 0.1 wt.% were observed for SWCNT/iPP and MWCNT/iPP nanocomposites, respectively. The formation of a conductive percolating network at such a low CNT concentration is favored by the high intrinsic conductivity and the low viscosity of the polymer matrix. The electrical percolation threshold of the iPP-based system was found to be lower than its rheological percolation threshold. Beyond the percolation threshold, MWCNT-based nanocomposites generally exhibited higher conductivity levels than those based on SWCNTs, most probably due to the higher intrinsic conductivity of the MWCNTs as compared to that of the SWCNTs. These excellent electrical properties, associated with the strong nucleating effect of the CNTs reported earlier [1] and [2], render this type of nanocomposites extremely attractive from a technological point of view.     

具有隔离结构的聚丙烯/碳纳米管复合材料的制备及电磁屏蔽性能

通过共挤出包覆-热压法制备了具有隔离结构的聚丙烯(PP)/碳纳米管(CNTs)电磁屏蔽复合材料。 其中,CNTs随机分布于PP基体中形成导电相,该导电复合物作为包覆层包敷在纯PP颗粒表面,形成包覆复合粒子,经热压后形成隔离导电网络。 结果表明,所制备的隔离结构复合材料呈现良好的导电性能,可获得较低的导电逾渗值0.28%(体积分数);在CNTs质量分数为5.6%时,该复合材料电磁屏蔽性能达到25.6 dB,同时具有良好的力学性能。 本文结果表明,共挤出包覆-热压法制备隔离结构导电复合材料方法简单可控、绿色环保,对开发高性能电磁屏蔽复合材料具有重要指导意义。     

Multiscale carbon nanotube-carbon fiber reinforcement for advanced epoxy composites

We report an approach to the development of advanced structural composites based on engineered multiscale carbon nanotube-carbon fiber reinforcement. Electrophoresis was utilized for the selective deposition of multi- and single-walled carbon nanotubes (CNTs) on woven carbon fabric. The CNT-coated carbon fabric panels were subsequently infiltrated with epoxy resin using vacuum-assisted resin transfer molding (VARTM) to fabricate multiscale hybrid composites in which the nanotubes were completely integrated into the fiber bundles and reinforced the matrix-rich regions. The carbon nanotube/carbon fabric/epoxy composites showed approximately 30% enhancement of the interlaminar shear strength as compared to that of carbon fiber/epoxy composites without carbon nanotubes and demonstrate significantly improved out-of-plane electrical conductivity.     

Electrical properties study of multi-walled carbon nanotubes/hybrid-glass nanocomposites

Electrical properties of multi-walled carbon nanotubes (MWNTs)/hybrid-glass nanocomposites prepared by the fast-sol–gel reaction were investigated in light of percolation theory. A good correlation was found between the experimental results and the theory. We obtained a percolation threshold ? _c  = 0.22 wt%, and a critical exponent of t = 1.73. These values are reported for the first time for a silica-based system. The highest conductivity measured on the MWNT/hybrid-glass nanocomposites was σ ≈ 10^?3(Ω cm)^?1 for 2 wt% carbon nanotube (CNT) loading. The electrical conductivity was at least 12 orders of magnitude higher than that of pure silica. Electrostatic force microscopy and conductive-mode atomic force microscopy studies demonstrated conductivity at the micro-level, which was attributed to the CNT dispersed in the matrix. It appears that the dispersion in our MWNT/hybrid-glass system yields a particularly low percolation threshold compared with that of a MWNT/silica-glass system. Materials with electrical conductivities described in this work can be exploited for anti-static coating.     

Conductive mechanism of polymer/graphite conducting composites with low percolation threshold

Preparation of the conducting composites of polystyrene/expanded graphite via in situ polymerization and investigation of the conductive mechanism were carried out. They are characterized by high conductivity and a low percolation threshold. The electrical conductivity reached 10^?2 S/cm with 3.0 vol % expanded graphite content, whereas the percolation threshold was 1.0 vol %. Optical micrographs revealed the heterogeneous distribution of the graphite particles and the formation of a conductive network in the polymer matrix. A model of primary particle was proposed to interpret the conductive phenomena. The primary particle is the basic conductive unit in the composites that comprises three of the following parts: the graphite particle, the compact‐adsorbed layer, and the wrapping shell. Our model was also used to explain the experimental data in our previous studies on nylon‐6/expanded graphite composites. A low percolation threshold of conducting composites can be also explained according to the model of the primary particle. Furthermore, the theoretical line of conductivity versus primary particle content calculated from the revised Flory's theory fits the experimental data well. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 954–963, 2002     

两种碳材料混合填充聚合物复合材料的导电特性及渗流阈值的计算模型

介绍了用碳纳米管与炭黑（或石墨）混合填充的聚合物复合材料的导电特性;阐述了混合填充聚合物体系的导电机理;介绍了基于线性混合规则和已占体积理论的渗流阈值的计算模型;分析了模型计算值与实验值的差异。利用已占体积理论,重新推导了混合填充体系渗流阈值的计算公式,并与文献公式做了比较。新公式表明：混合填充聚合物复合材料的渗流阈值...     

磺化聚苯乙炔/多壁碳纳米管复合材料导电机理研究

将磺化聚苯乙炔(SPPA)与多壁碳纳米管(MWNT)超声共混制备得到SPPA/MWNT复合材料. 用四探针电阻率测试、场发射扫描电镜(FESEM)、XPS、UV-Vis、XRD等方法对复合材料导电机理进行研究. 结果表明, SPPA/MWNT的电导率发生两次突跃；掺杂剂MWNT具有低的临界阈值; 临界阈值附近, 复合材料中MWNT具有不连续分布的现象及复合材料电阻呈负温度系数(NTC)效应; SPPA/MWNT复合材料中MWNT的碳原子对SPPA 进行掺杂. 推测复合材料的导电机理为, 共轭聚合物SPPA不仅被导电粒子MWNT物理填充, 同时还被MWNT的碳原子掺杂, 使复合材料中存在两种导电通路而导电, 一是因被掺杂而成为高电导率主体的SPPA相互接触形成的导电通路, 二是MWNT相互接触形成的导电通路.     

The effect of crystallization behavior on high conductivity,enhanced mechanism and thermal stability of poly(ε-caprolactone)/multi-walled carbon nanotube composites

Poly(ε-caprolactone) (PCL) composites filled by multi-walled carbon nanotubes (MWCNTs) which was non-covalently modified by the combined surfactants of poly(sodium 4-styrenesulfonate) and cetyltrimethyl-ammonium bromide (PSS-CTAB) were fabricated via simple solution precipitation method. PCL/MWCNTs composites provided with the low procolation threshold (0.4?wt%) and high electrical conductivity due to good dispersion of MWCNTs. And the excellent mechanical properties and enhanced thermal stability were also obtained with the addition of modified MWCNTs. In addition, all PCL composites showed significantly enhanced crystallization with increasing the MWCNTs contents, which demonstrated that the MWCNT-induced crystallization of PCL could effectively regulate the properties of composites. In a word, introducing non-covalent functionalized MWCNTs in the polymer system was a promising way for developing excellent conductive composites.     

Multiwalled Carbon Nanotubes Produced by a Continuous CVD Method and Their Use in Melt Mixed Composites with Polycarbonate

Summary: In this study, two samples of multiwalled carbon nanotubes (MWNT) were synthesized by CVD of acetylene over Fe₂Co catalysts supported by CaCO₃ using different temperatures. The material produced at 660 °C (MWNT600) shows slightly better performance as evidenced by lower mean tube diameter and better conductivity as compared to the sample produced at 700 °C (MWNT700). In addition, it has a higher [O]:[C] ratio. Both materials were incorporated into polycarbonate using melt mixing using a small scale compounder. The results prove that these materials are very suitable for polymer composite applications as they show low electrical percolation concentration and good mechanical enhancement. The percolation threshold is as low as <0.875 wt% for MWNT660 and <1 wt% for MWNT700. MWNT700 showed slightly better dispersability as evidenced from light microscopy, SEM, and TEM. The effects in the stress-strain curves are similar in both composites, indicating a stress increase with MWNT incorporation.     

Enhanced conductivity composites for aircraft applications: carbon nanotube inclusion both in epoxy matrix and in carbonized electrospun nanofibers

The potential of carbonized electrospun nanofiber mats to render epoxy resin composites for aircraft applications electrically and thermally more conductive was investigated. The effect of carbon nanotube inclusion both inside the carbon nanofiber and in the epoxy resin matrix material was studied, in order to reveal any synergistic effects of multilevel presence of nanosized reinforcements on the conductivity and mechanical properties. The carbon nanotube inclusion into the carbonized nanofibers increased the electrical conductivity of the samples by 20–50% and the thermal conductivity by approximately three times leading to a higher value than that of the conventional composites. The preparation of layered composites with a conductive upper layer containing nonwoven carbon nanofabric and a load bearing lower layer with conventional unidirectional carbon fiber reinforcement can offer a cost‐effective and weight‐saving solution for the replacement of metal meshes in structural aircraft composites. Copyright © 2014 John Wiley & Sons, Ltd.     

A Novel Method for Preparing Polyurethane Based Conductive Composites with Low Percolation Threshold

A novel method for preparing conductive carbon black filled polymer composites with low percolation threshold from polyurethane emulsion are reported in this paper. The experimental results indicate that with a rise in carbon black concentration the insulator-conductor transition in the emulsion blended composites occurs at 0.8-1.4vol%. In contrast, the solution blended composites exhibit drastic increase in conductivity at conducting filler fraction as high as 12.3-13.3vol%. It is demonstrated that the composites microstructure rather than chemical structure of the matrix polymer predominantly determines the electrical conduction performance of the composites.     

Preparation of a polyacetylene composite with single-walled carbon nanotubes and study of its electrochemical properties

A composite consisting of single-walled carbon nanotubes (2.4 wt %) covered by polyacetylene has been prepared. Polyacetylene synthesized directly on single-walled carbon nanotubes is a defectless long-chain polymer composed of trans and cis units with a sufficient length (60% trans and 40% cis isomers). An appreciable acceleration of the lithium ion intercalation-deintercalation corresponds to an increase in the conductivity of the composite material near the percolation threshold. The polyacetylene layer on single-walled carbon nanotubes plays the role of an electrochemically active ion-conductive membrane suitable for the transport of Li⁺ cations to the surface of nanotubes.     

The development of conductive carbon nanotube network in polypropylene-based composites during simultaneous biaxial stretching

The development of electronic conducting networks during the simultaneous biaxial stretching of isotactic polypropylene/carbon nanotube (iPP/CNT) composites was investigated. During the stretching process, the electrical resistivity of the composites was found to be very sensitive to the draw ratios. This was especially true at CNT concentration close to the percolation threshold, ca. 2.2 vol.%. The resistivity–draw ratio dependence was divided into two stages. In the first stage, the stretching was taken by the amorphous zones and only led to the enlargement of the distance between CNT aggregates. This resulted in the breaking of the conductive network and, consequently, a sharp increase in resistivity. As the turning point was approached, individual nanotubes started to disentangle from CNT aggregates. Meanwhile, the resistivity of the stretched films was dramatically decreased by 7 orders of magnitude, indicating a rebuilding of the conducting network during the biaxial stretching process.     

Polycarbonate carbon nanofiber composites

Carbon nanofiber (CNF) composites have the potential for creating inexpensive, semiconducting polymers. These composites require a homogeneous dispersion within the polymer. Many groups have focused on high shear methods such as twin screw extrusion. Although high shear methods produce a homogeneous dispersion, the aspect ratio of the nanofibers is reduced by the mechanical force. In this report, we present results for low shear composite formation via in situ polymerization of cyclic oligomeric carbonates. The composites were characterized by thermal gravimetric analysis, electrical conductivity, scanning electron microscopy and transmission electron microscopy. The composites exhibit minimal aggregation of the carbon nanofibers even at high weight percents. The polycarbonate/CNF composites exhibit an electrical conductivity percolation threshold of 6.3 wt% which is higher compared with similar CNF composites. The composites also show an increase in thermal stability of 40 °C as the CNF loading increases from 0 to 9 wt%.