Comparison of electrical properties between multi-walled carbon nanotube and graphene nanosheet/high density polyethylene composites with a segregated network structure

Multi-walled carbon nanotube (MWCNT)/high density polyethylene (HDPE) and graphene nanosheets (GNS)/HDPE composites with a segregated network structure were prepared by alcohol-assisted dispersion and hot-pressing. Instead of uniform dispersion in polymer matrix, MWCNTs and GNSs distributed along specific paths and formed a segregated conductive network, which results in a low electrical percolation threshold of the composites. The electrical properties of the GNS/HDPE and MWCNT/HDPE composites were comparatively studied, it was found that the percolation threshold of the GNS/HDPE composites (1 vol.%) was much higher than that of the MWCNT/HDPE composites (0.15 vol.%), and the MWCNT/HDPE composite shows higher electrical conductivity than GNS/HDPE composite at the same filler content. According to the values of critical exponent, t, the two composites may have different electrical conduction mechanisms: MWCNT/HDPE composite represents a three-dimensional conductive system, while the GNS/HDPE composite represents a two-dimensional conductive system. The improving effect of GNSs as conducting fillers on the electrical conductivity of their composites is far lower than theoretically expected.     

Poly(3-hexylthiophene) wrapped carbon nanotube/poly(dimethylsiloxane) composites for use in finger-sensing piezoresistive pressure sensors

We fabricated a piezoresistive composite using multi-walled carbon nanotubes (MWCNTs) as a conductive filler and polydimethylsiloxane (PDMS) as a polymer matrix, which operated in the extremely small pressure range required for finger-sensing. To achieve a homogeneous dispersion of MWCNTs in PDMS, the MWCNTs were modified by a polymer wrapping method using poly(3-hexylthiophene) (P3HT). The percolation threshold of the composites was significantly lowered by the presence of P3HT. The electrical conductivity and piezoresistive sensitivity of the composite were found to strongly depend on the P3HT concentration. The well-dispersed P3HT-MWCNT/PDMS composite showed good piezoresistive characteristics in the 0–0.12 MPa pressure range.     

Effect of processing methods and functional groups on the properties of multi-walled carbon nanotube filled poly(dimethyl siloxane) composites

Pristine and functionalized multi-walled carbon nanotubes (MWCNTs) filled poly(dimethyl siloxane) (PDMS) composites were produced by two different methods, namely the solution mixing method and the mini-extruder method. The composites produced using the mini-extruder exhibit relatively higher tensile strength and higher thermal conductivity due to better nanotubes dispersion. On the other hand, the composites prepared via solution mixing have higher electrical conductivity and better thermal stability due to the high aspect ratio of nanotubes. Scanning electron micrographs of composites fracture surface revealed that composites produced by mini-extruder resulted shorter nanotube length, thus lowering the aspect ratio of MWCNTs. In general, functionalization of nanotubes increases the tensile strength, thermal conductivity, and thermal stability of the PDMS composites due to the improved interfacial adhesion and nanotubes dispersion.     

Enhanced positive temperature coefficient in amorphous PS/CSPE-MWCNT composites with low percolation threshold

In this work, amorphous polystyrene/chlorosulfonated polyethylene composites doped with multiwalled carbon nanotubes (PS/CSPE-MWCNT) were constructed by in situ polymerization to form semi-interpenetrating networks. The MWCNTs showed excellent dispersion and selective location in the PS regions. High electrical conductivity and low percolation threshold (0.89 wt %) for the composites were achieved. An enhanced positive temperature coefficient (PTC) behavior for amorphous PS/CSPE-MWCNT composites was first reported, nearly without a negative temperature coefficient (NTC) effect when the conductive fillers were beyond the percolation threshold, similar to those of crystalline polymer composites. Moreover, a PTC intensity of more than five orders of magnitude and excellent repeatability of the PTC effect were achieved. This study offers new insight into the development of novel PTC materials with low percolation threshold. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47053.     

Simultaneous enhancement of electrical conductivity and interlaminar shear strength of CF/EP composites through MWCNTs doped thermoplastic polyurethane film interleaves

Carbon fiber-reinforced epoxy (CF/EP) composites have been widely used in aerospace industry, while poor electrical conductivity and interlaminar shear fracture toughness could reduce their safety as structural components in use. In this work, we achieved simultaneous improvement in electrical conductivity and interlaminar shear strength through interleaved multi-walled carbon nanotubes (MWCNTs) doped thermoplastic polyurethane (TPU) conductive thin films (CTFs), which were prepared by a solution casting method. The experimental results showed that the electrical conductivity of the laminates increased by about 13 and 16 times in the transverse and thickness directions with only about 1 wt % MWCNTs content in the laminates. The end-notch flexure (ENF) tests showed that the mode II interlaminar fracture toughness (G_IIC) of composites with 10 wt % MWCNTs CTF interleaf shows a significant increase of about 106%. The enhancement mechanism was further explored through microscopic morphological observation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47988.     

Non-destructive functionalization of multi-walled carbon nanotubes with naphthalene-containing polymer for high performance Nylon66/multi-walled carbon nanotube composites

A new compatibilizer, poly(vinyl benzyloxy methyl naphthalene)-g-poly(t-butyl methacrylate-co-methacrylic acid), was synthesized for Nylon 66 (N66)/multi-walled carbon nanotube (MWCNT) composites. It has been shown that the naphthalene unit in the main chain of the compatibilizer interacts with MWCNTs by π–π interaction and that the carboxylic acid unit in the graft chain of the compatibilizer interacts with the amide group of N66. The use of the compatibilizer produces well-dispersed MWCNTs in N66 matrix, which results in improved mechanical and electrical properties of the composites, while the simple mixture of N66/MWNCTs without the compatibilizer exhibits poor mechanical and electrical properties due to severe aggregation of MWCNTs. It is also found that the compatibilizer with a small amount of carboxylic acids is more effective for improving the mechanical and electrical properties of N66/MWCNT composites.     

Property reinforcement of acrylonitrile‐butadiene‐styrene by simultaneous incorporation of carbon nanotubes and self‐prepared copper particles

In this article, copper (Cu) crystallites were successfully prepared via low temperature molten salt method, and the possible formation mechanisms were proposed. The conductive fillers of multiwalled carbon nanotubes (MWCNTs) and as‐prepared Cu particles were designed and introduced into acrylonitrile‐butadiene‐styrene (ABS) blend to prepare different conductive composites. The dispersion states of conductive fillers and the morphologies of the composites were characterized using a field emission scanning electron microscope. The electrical resistivity of different composites was measured. The results showed that Cu and MWCNTs exhibited a synergistic effect in decreasing the electrical resistivity of the Cu/MWCNTs/ABS composites, because Cu that could locate between MWCNTs chain segments provides a better charge transport in the conductive pathways. Compared with pure ABS, the tensile strength, elastic modulus and thermal stability of the Cu/MWCNTs/ABS composites were significantly improved with the incorporation of Cu and MWCNTs. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41738.     

黏土对聚己二酰间苯二甲胺/碳纳米管复合材料导电性能的影响

采用熔融复合法制备并研究了聚己二酰间苯二甲胺/多壁碳纳米管（MXD6/MWCNT）复合材料的导电性能。结果表明,MXD6和MWCNT之间的相容性较差,体系中大部分MWCNT倾向于处于团聚状态,使MWCNT构建导电网络的效率大大降低;而添加有机蒙脱土（OMMT）可显著提高复合材料的导电性能,如在MWCNT含量为2份（质量份,下同）的体系中,添加OMMT可使体系的体积电阻率急剧降低7个数量级;OMMT的作用机制在于其在材料混炼过程中,使MWCNT不断分散并承载于更新的OMMT粒子表面上,形成空间上具有高次结构的结构形态,因而极大地改善了导电网络的构筑效率。     

Investigation of the rheological and conductive properties of multi-walled carbon nanotube/polycarbonate composites by positron annihilation techniques

The microstructure, rheological and conductive properties of multi-walled carbon nanotube (MWCNT)/polycarbonate (PC) composites were investigated by positron annihilation lifetime spectroscopy, positron annihilation coincidence Doppler broadening (CDB), oscillatory rheometry and electrical resistivity for different MWCNT contents. A 10 orders of magnitude increase in electrical conductivity was achieved with very small quantities of MWCNTs. CDB was used to determine a percolation threshold value, which was in good agreement with the electrical conductivity and rheological measurements. The results showed that with increasing MWCNT content, the composites underwent a phase transition from insulating to conducting at room temperature, which was attributed to the formation of a MWCNT network. The effect of MMCNTs on the microstructure of MWCNT/PC composites has been studied by positron annihilation lifetime measurements. The results showed that the fractional free volume decreased because of the MWCNTs and the formation of conductive network. The effects of MWCNT filler on the atomic scale free volume and mechanical property of MWCNT/PC composites were also discussed.     

Effects of multi‐walled carbon nanotubes and conductive carbon black on electrical,dielectric, and mechanical properties of epoxidized natural rubber composites

The influence of multi‐walled carbon nanotubes (MWCNTs) and conductive carbon black (CCB) on cure, electrical, dielectric, and mechanical properties of epoxidized natural rubber (ENR) composites was investigated. It was found that short MWCNTs (S‐MWCNTs) with low loading significantly affected the cure characteristics in a way similar to high loading of CCB. Moreover, the ENR/S‐MWCNTs composites exhibited high AC conductivity, dielectric constant, and dielectric loss tangent (tan δ ) compared to the ENR/CCB and ENR/L‐MWCNTs (long MWCNTs) composites. In addition, the S‐MWCNTs composites showed the lowest percolation threshold concentration, defined as the lowest loading to form conductive paths in the insulating ENR matrix. This might be attributed to the comparatively high interfacial polarization, with good dispersion and distribution, of the S‐MWCNTs in ENR matrix. These characteristics were confirmed by TEM imaging and by a high bound rubber content, corroborating strong filler–rubber interactions in the ENR/S‐MWCNTs composites. However, the L‐MWCNTs composites showed the lowest electrical and other related properties, despite the highest aspect ratio and specific surface area of this filler. This might be because of the flocculation of nanotubes by mutual entanglement, leading to a poor uneven distribution in the ENR matrix. POLYM. COMPOS., 38:1031–1042, 2017. © 2015 Society of Plastics Engineers     

Electrical conductivity of carbon nanotube/poly(vinylidene fluoride) composites prepared by high-speed mechanical mixing

Electrically conductive multi-walled nanotube (MWCNT)/poly(vinylidene fluoride) (PVDF) composites with a segregated structure were prepared by high-speed mechanical mixing method. It was found that MWCNTs were uniformly dispersed on polymer particle surfaces. At the MWCNTs composition of 0.1 vol.%, the composites exhibited a dramatic enhancement in electrical conductivity by 11 orders of magnitude. A low percolation threshold was achieved at the CNT concentration of 0.078 vol.%. The mechanical mixing method presented can be adapted to other CNT/polymer composites with a segregated structure.     

Influence of the viscosity ratio in PC/SAN blends filled with MWCNTs on the morphological,electrical, and melt rheological properties

Co-continuous polycarbonate (PC)/poly(styrene-acrylonitrile) (SAN) = 60/40 wt.% blends were filled with 1 wt.% multi-walled carbon nanotubes (MWCNTs), which selectively localized within the PC component. To study the influence of the viscosity ratio, PCs with different viscosities were selected resulting in PC/SAN viscosity ratios (at 100 rad/s) between 1.2 and 4.5. With increasing viscosity ratio, smaller blend structures were observed. Furthermore, optical microscopy revealed that the filler dispersion was improved with decreasing PC viscosity. The highest electrical conductivity was achieved for the blend composite with the coarsest morphology, containing the low viscosity PC and having the lowest PC/SAN viscosity ratio. Transmission electron microscopy analysis indicated that for the composite prepared with high viscosity PC, not all of the incorporated MWCNTs were able to localize completely into the PC component. Instead, some MWCNTs were found to be stacked at the interface of the two polymers, indicating that the high PC melt viscosity had a restricting effect on the movement of the MWCNTs. Moreover, with electrical conductive atomic force microscopy, it was proven that small, spherical PC particles, even if filled with CNTs, do not take part in the conductive network of the blend composites. Rheological analyses showed a correlation with the morphological analysis and the electrical conductive behavior of the blend composites. In summary, a lower viscosity ratio between the blend components, in which upon addition due to thermodynamic reasons the CNTs localize (here PC), and the other component (here SAN) is favorable for high electrical conductivity values.     

Noncovalent compatibilization of polypropylene/MWCNT composites using an amino‐pyridine grafted polypropylene matrix

Polypropylene (PP)/multiwalled carbon nanotube (MWCNT) composites are prepared by implementing noncovalent compatibilization. The compatibilization method involves PP matrix functionalization with pyridine (Py) aromatic moieties, which are capable of π–π interaction with MWCNT sidewalls. Imaging revealed that the addition of 25 wt% of PP‐g‐Py to neat PP is capable of drastically reducing nanotube aggregate size and amount, compared to a matrix containing the equivalent amount of a maleated PP (PP‐g‐MA). Raman spectroscopy confirms improved polymer/nanotube interaction with the PP‐g‐Py matrix. The electrical percolation threshold appears at a MWCNT loading of approximately 1.2 wt%, and the maximum value of the electrical conductivity achieved is 10⁻² S/m, irrespective of the functionalization procedure. The modulus of the composites is improved with the addition of MWCNTs. Furthermore, composites functionalized with Py display significant improvements in composite ductility compared with their maleated counterparts because of the improved filler dispersion. POLYM. COMPOS., 37:2794–2802, 2016. © 2015 Society of Plastics Engineers     

5‐Sulfoisophthalic acid monolithium salt doped polypyrrole/multiwalled carbon nanotubes composites for EMI shielding application in X‐band (8.2–12.4 GHz)

This article describes the synthesis and characterization of highly conductive polypyrrole (PPy)/multiwalled carbon nanotube (MWCNT) composites prepared by in situ polymerization of pyrrole using 5‐sulfoisophthalic acid monolithium salt [lithio sulfoisophthalic acid (LiSiPA)] as dopant and ferric chloride as oxidant. Several samples were prepared by varying the amounts of MWCNTs ranging from 1 to 5 wt %. Scanning electron microscope and transmission electron microscope images clearly show a thick coating of PPy on surface of MWCNTs. The electrical conductivity of PPy increased with increasing amount of MWCNTs and maximum conductivity observed was 52 S/cm at a loading of 5 wt % of MWCNTs. Pure PPy prepared under similar conditions had a conductivity of 25 S/cm. Electromagnetic interference (EMI) shielding effectiveness (SE) also showed a similar trend and average EMI shielding of ?108 dB (3 mm) was observed for sample having 5 wt % MWCNT in the frequency range of 8.2–12.4 GHz (X‐band). The light weight and absorption dominated total SE of ?93 to ?108 dB of these composites indicate the usefulness of these materials for microwave shielding. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45370.     

Conductive sizing for improving electrical conductivity of carbon fiber/polyaryl ether ketone/AgNWs composites

The aim of this work is to enhance the electrical conductivity of PAEK/continuous carbon fiber (CF) composites while maintaining their mechanical properties. A conductive sizing was elaborated by mixing polyetherimide (PEI) with silver nanoplates (AgNpts) in suspension in dichloromethane. An aqueous PEI formulation was used as insulating sizing reference. The presence of AgNpts into the sizing enhances electrical conductivity up to 0.2 S.m⁻¹ for a silver content ∼ 0.2 vol % without any modification of mechanical properties. The influence of conductive sizing on PAEK–AgNWs/CF was observed. For low AgNWs content lower (<1 vol %); the conductive sizing increases the electrical conductivity of the composite by one decade. This result shows that both types of Ag particles participate to the conductive path. For higher AgNWs content, electrical conductivity (200 S.m⁻¹) is independent from the AgNpts content: the conductive path is only constituted by AgNWs. Mechanical properties of such composites show that the value of the conservative modulus is almost the same, while the dissipative modulus slightly increases. The global mechanical properties of the composite are preserved despite the addition of the CF, AgNWs, and AgNpts. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47872.     

EP/GNs/MWCNTs复合材料的导热性能

以多壁碳纳米管(MWCNTs)和石墨烯纳米微片(GNs)为导热填料,环氧树脂(EP)为基体采用溶剂和超声分散法,制备了EP/GNs/MWCNTs导热复合材料,并与EP/MWCNTs及EP/GNs复合材料的导热性能进行了对比。采用透射电子显微镜观察其微观结构,采用Hot Disk热导率测试仪测试其导热性能,采用差示扫描量热法和热重分析仪测试其耐热性及热稳定性。结果表明,MWCNTs和GNs共同作为EP导热填料时,相比于单组分填料(MWCNTs或GNs)更易形成导热网络;EP的热导率、玻璃化转变温度(Tg)和热分解温度均随着MWCNTs或GNs含量的增加而提高,其中,GNs更有利于提高EP的热导率和热分解温度,MWCNTs更有利于提高EP的Tg。在相同的导热填料含量下,相对于其中的任一单一填料,MWCNTs/GNs共同作用时,对热导率的提高有更显著的效果,且随着其中GNs比例的增加,热导率逐渐增大。当GNs和MWCNTs的体积分数分别为0.6%和0.4%时,EP/GNs/MWCNTs复合材料的热导率、Tg和起始分解温度分别为0.565 W/(m·K),152℃和316℃,分别比纯EP提高了132.5%,34.5%和8.2%。     

Preparation, crystallization, electrical conductivity and thermal stability of syndiotactic polystyrene/carbon nanotube composites

A homogeneous dispersion of multi-walled carbon nanotubes (MWCNTs) in syndiotactic polystyrene (sPS) is obtained by a simple solution dispersion procedure. MWCNTs were dispersed in N-methyl-2-pyrrolidinone (NMP), and sPS/MWCNT composites are prepared by mixing sPS/NMP solution with MWCNT/NMP dispersion. The composite structure is characterized by scanning electron microscopy and transmission electron microscopy. The effect of MWCNTs on sPS crystallization and the composite properties are studied. The presence of MWCNTs increases the sPS crystallization temperature, broadens the crystallite size distribution and favors the formation of the thermodynamically stable β phase, whereas it has little effect on the sPS γ to α phase transition during heating. By adding only 1.0 wt.% pristine MWCNTs, the increase in the onset degradation temperature of the composite can reach 20 °C. The electrical conductivity is increased from 10^{−10∼−16} (neat sPS) to 0.135 S m⁻¹ (sPS/MWCNT composite with 3.0 wt.% MWCNT content). Our findings provide a simple and effective method for carbon nanotube dispersion in polymer matrix with dramatically increased electrical conductivity and thermal stability.     

Electrical conductivity and dynamic mechanical properties of silicon rubber‐based conducting composites: effect of cyclic deformation,pressure and temperature

The effects of cyclic deformations such as bending and compressive flexing, temperature and pressure on electrical and dynamic mechanical properties of conductive polydimethylsiloxane (PDMS) composites have been investigated. Conductive elastomeric composites were prepared by incorporating various carbon blacks in insulating PDMS matrix. Electrical conductivity was measured against varying concentration of different carbon blacks to assess the percolation threshold of the composites. AC and DC conductivity was found to increase with an increase in some bending flex cycles. However, with compressive flexing, DC conductivity initially dropped but later started increasing with an increase in flex cycles. The variations in electrical conductivity and dynamic mechanical modulus due to bend flexing are found to be similar, i.e. both characteristics show an increase in magnitude with an increase in some flex cycles. DC resistivity was found to increase with heating–cooling cycles, and this change in resistivity did not follow the same path leading to electrical set and hysteresis. © 2017 Society of Chemical Industry     

Effects of carbon nanotubes aspect ratio on the qualitative and quantitative aspects of frequency response of electrical conductivity and dielectric permittivity in the carbon nanotube/polymer composites

To study the effect of carbon nanotube aspect ratio (AR) on the frequency response of the electrical properties, the alternating current (AC) electrical conductivity and dielectric permittivity of different AR multi-wall carbon nanotubes (MWCNTs)/thermoplastic elastomer (TPE) composites were studied in the AC frequency range of 100 Hz to 10  MHz. Qualitatively, the effect of frequency on the electrical properties of the composites was the same for all AR MWCNTs and shared many typical features of electrically percolative composites. Quantitatively, the frequency responses of electrical properties were found to be independent of nominal AR, concentration, percolation threshold, and the diameter of the MWCNT. Instead, frequency response of electrical properties was dependent on the MWCNT length and initial electrical conductivity of the composites. With the same initial conductivity of the MWNT composites, frequency-conductivity sensitivity varied inversely with the nominal length of the MWCNTs. Composites with MWCNTs of the same nominal length and similar electrical conductivity values, regardless of whether the MWCNT concentration was below or above the percolation threshold, exhibited quantitatively similar frequency-conductivity sensitivity. The frequency-dielectric sensitivity at the percolation threshold was a reflection of frequency-conductivity sensitivity and was also found to be dependent on the initial conductivity of the composites.     

Preparation and properties of polyurethane/multiwalled carbon nanotube nanocomposites by a spray drying process

A spray drying approach has been used to prepare polyurethane/multiwalled carbon nanotube (PU/MWCNT) composites. By using this method, the MWCNTs can be dispersed homogeneously in the PU matrix in an attempt to improve the mechanical properties of the nanocomposites. The morphology of the resulting PU/MWCNT composites was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and TEM observations illustrate that the MWCNTs are dispersed finely and uniformly in the PU matrix. X‐ray diffraction results indicate that the microphase separation structure of the PU is slightly affected by the presence of the MWCNTs. The mechanical properties such as tensile strength, tensile modulus, elongation at break, and hardness of the nanocomposites were studied. The electrical and the thermal conductivity of the nanocomposites were also evaluated. The results show that both the electrical and the thermal conductivity increase with the increase of MWCNT loading. In addition, the percolation threshold value of the PU composites is significantly reduced to about 5 wt % because of the high aspect ratio of carbon nanotubes and exclusive effect of latex particles of PU emulsion in dispersion. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012