Lowering the percolation threshold of conductive composites using particulate polymer microstructure

The percolation thresholds of carbon black–polymer composites have been successfully lowered using particulate polymer starting materials (i.e., latex and water‐dispersible powder). Composites prepared using carbon black (CB) and commercial poly(vinyl acetate) (PVAc) latex exhibit a percolation threshold near 2.5 vol % CB. This threshold value is significantly lower than that of a comparable reference composite made from poly(N‐vinylpyrrolidone) (PNVP) solution and the same CB, which exhibits a sharp rise in electrical conductivity near 15 vol % CB. This dramatic difference in critical CB concentration results from the segregated microstructure induced by the latex during composite film formation. Carbon black particles are forced into conductive pathways at low concentration because of their inability to occupy volume already claimed by the much larger latex particles. There appears to be good qualitative agreement between experimental findings and current models dealing with conductive behavior of composites with segregated microstructures. Lack of quantitative agreement with the models is attributed to the polydispersity of the polymer particles in the latex. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 692–705, 2001     

不同炭黑对聚丙烯／炭黑复合材料导电性能的影响

研究了四种不同的导电炭黑与聚丙烯复合制得的复合材料的体积电阻率与炭黑含量的关系，确定了复合体系中炭黑的渗滤阈值。用扫描电镜(SEM)观察了不同炭黑含量的复合材料的断面形貌，用透射电镜(TEM)观察分析了四种炭黑的结构及粒径，并对其比表面积进行了测定。结果表明：炭黑不同，得到的复合材料的渗滤阈值有很大差别。炭黑结构性越高，比表面积越大，粒径越小，其导电性能越好，得到的渗滤阈值越低。特别是具有空壳结构的炭黑，其渗滤阈值明显低于其他三种炭黑。     

Evaluation of the rheological and electrical percolation of high-density polyethylene/carbon black composites using mathematical models

In this work, conductive polymer composites (CPCs) of bio-based polyethylene (BioPe) containing different concentrations of carbon black (CB) were developed. By using oscillatory rheology analysis, a Newtonian plateau was observed in BioPe, and all BioPe/CB composites had a behavior of a pseudo-solid and that composites with volume fractions ranging from 0.24 to 0.56 presented higher viscosity, storage, and loss modulus. This suggests the formation of a percolated network and by using the power-law models, it was observed that the electrical percolation threshold was higher than the rheological percolation threshold. The electrical conductivity was measured using the four-point probe method and a sigmoid model was used to predict the CPCs' electrical conductivity percolation threshold. The results indicated that the four-point probe method presented satisfactory results according to the calculated standard deviations and voltage–current characteristics for each round of measurements considering the same ranging as used in rheology analysis. The analytical model used showed a coefficient of determination (R²) higher than 95%, allowing the prediction of the electrical conductivity of the CPC and the percolation threshold as a function of the volumetric fraction of the CB.     

Submicron copper‐low‐density polyethylene conducting composites: Structural,electrical, and percolation threshold

Copper‐embedded low‐density polyethylene (LDPE) composites were fabricated using different copper concentrations in the polymer matrix. The copper particles were spherical with a mean particle size between 200 and 300 nm. All the samples were compacted under pressure and melted. The LDPE matrix was analyzed using gel permeation chromatography (GPC) and it did not evidence degradation of the LDPE matrix. The microstructure of the composites was examined with scanning electron microscopy. The electrical conductivity was measured as a function of the copper content, and the composite fabricated with a 10 vol % copper presented a conductivity 15 orders of magnitude higher than that of pure LDPE. The enhancement in conductivity can be explained by means of segregated percolation path theory and the experimental results are in agreement with the theoretical law. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Electrical,rheological, and mechanical properties copolymer/carbon black composites

This work aims to evaluate the electrical conductivity and the rheological and mechanical properties of copolymer/carbon black (CB) conductive polymer composites (CPCs). The copolymers, containing ethylene groups in their structure, used as matrix were polyethylene grafted with maleic anhydride (PEgMA), ethylene-methyl acrylate–glycidyl methacrylate (EMA-GMA), and ethylene-vinyl acetate (EVA). For comparison purposes, bio-based polyethylene (BioPE)/CB composites were also studied. The electrical conductivity results showed that the electrical percolation threshold of BioPE/CB composite was 0.36 volume fraction of CB, whereas the rheological percolation threshold was 0.25 volume fraction of CB. The most conductive CPC was BioPE/CB. Among the copolymer/CB CPCs, PEgMA/CB showed the highest conductivity, which can be attributed to the fact that the PEgMA copolymer had higher crystallinity. It also has a higher amount of ethylene groups in its structure. Torque rheometry analysis indicated that EMA-GMA copolymer may have reacted with CB. Rheological measurements under oscillatory shear flow indicated the formation of a percolated network in BioPE/CB and copolymer/CB composites. Morphology analysis by scanning electron microscopy (SEM) indicated the formation of a percolated network structure in BioPE/CB composite and finely dispersed CB particles within the PEgMA copolymer. Wetting of CB particles/agglomerates by the copolymer matrix was observed in EVA/CB and EMA-GMA/CB composites. Conductive CB acted as reinforcing filler as it increased the elastic modulus and tensile strength of BioPE and the copolymers.     

Preparation of carbon black/polypropylene nanocomposite with low percolation threshold using mild blending method

A new approach, mild blending method, to prepare carbon black (CB) filled polypropylene (PP) nanocomposite using CB aqueous suspension was reported in this study. In this compounding process, the CB particles were first dispersed in aqueous suspension by using an ultrasonic irradiation. Subsequently, the CB suspension was blended with melting PP using an extruder with low shear strength screw configuration, followed by removing the vapor from the vent by vacuum. The morphological observation showed that the CB particles were dispersed at a nanometer level in the nanocomposites as they were in aqueous suspension and distributed homogeneously in PP matrix. The CB/PP nanocomposite prepared by this method exhibited a very low percolation threshold, i.e., 2.49 vol %, and a high‐critical resistance exponent t (t = 5.82). These phenomena, which deviated from the classical percolation theory, were likely to come down to the homogeneous distribution of CB particles and the tunneling conduction. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Electrical,rheological and electromagnetic interference shielding properties of thermoplastic polyurethane/carbon nanotube composites

Electrically conducting rubbery composites based on thermoplastic polyurethane (TPU) and carbon nanotubes (CNTs) were prepared through melt blending using a torque rheometer equipped with a mixing chamber. The electrical conductivity, morphology, rheological properties and electromagnetic interference shielding effectiveness (EMI SE) of the TPU/CNT composites were evaluated and also compared with those of carbon black (CB)‐filled TPU composites prepared under the same processing conditions. For both polymer systems, the insulator–conductor transition was very sharp and the electrical percolation threshold at room temperature was at CNT and CB contents of about 1.0 and 1.7 wt%, respectively. The EMI SE over the X‐band frequency range (8–12 GHz) for TPU/CNT and TPU/CB composites was investigated as a function of filler content. EMI SE and electrical conductivity increased with increasing amount of conductive filler, due to the formation of conductive pathways in the TPU matrix. TPU/CNT composites displayed higher electrical conductivity and EMI SE than TPU/CB composites with similar conductive filler content. EMI SE values found for TPU/CNT and TPU/CB composites containing 10 and 15 wt% conductive fillers, respectively, were in the range ?22 to ?20 dB, indicating that these composites are promising candidates for shielding applications. © 2013 Society of Chemical Industry     

Effect of composite preparation techniques on electrical and mechanical properties and morphology of nylon 6 based conductive polymer composites

Nylon 6/carbon black conductive composites were prepared using two different methods, masterbatch dilution and melt mixing. Their effect on the size and distribution of carbon black agglomerates in the matrix was studied in terms of electrical and mechanical properties and morphology. The electrical resistivity of composites prepared by both methods decreased with increasing filler composition. The electrical resistivity of the diluted masterbatch composites and the melt mixed composites was reduced from the resistivity of pure nylon 6, 10¹⁵ “ohm, cm”, to 10⁷ “ohm, cm” at 1 and 6 wt % of carbon black, respectively. As the filler content increased, elongation at break and impact strength decreased, but tensile modulus increased. Masterbatch dilution method provided smaller carbon black clusters in composites compared to melt mixing method. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2520–2526, 2006     

Dynamic percolation phenomenon of poly(methyl methacrylate)/surface fluorinated carbon black composite

The electrical resistivity of polymer filled with conductive filler, such as carbon black (CB) particles, is greatly decreased by incorporating the conductive filler. This is called the percolation phenomenon and the critical CB concentration is called the percolation threshold concentration (Φ*). For CB particle–filled insulating polymer composite at lower than Φ*, the conductive CB network is constructed in the polymer matrix when the composite is maintained at a temperature higher than the glass‐transition temperature or the melting temperature of the polymer matrix. This phenomenon is called dynamic percolation and the time to reach the substantial decrease in resistivity is called percolation time (t_p). To investigate the relationship between the dynamic percolation process and the surface state of CB particles, we used three kinds of carbon black particles such as original carbon black (CB0) and fluorinated carbon black (FCB010 and FCB025)–filled poly(methyl methacrylate) (PMMA). It was observed that the dynamic percolation curves for CB0‐filled PMMA and FCB‐filled PMMA composites shifted to a shorter percolation time with increases in both the annealing temperature and the filler concentration. However, the dynamic percolation curves of FCB‐filled PMMA showed a gradually decreasing trend compared to that of CB0‐filled PMMA composites. The activation energy calculated from an Arrhenius plot of the t_p against the inverse of the annealing temperature was decreased by surface fluorine treatment. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1151–1155, 2003     

Electrical and thermal phenomena in low-density polyethylene/carbon black composites near the percolation threshold

Low-density polyethylene (LDPE)/carbon black (CB) composites were fabricated via melt-compounding technique. The percolation threshold was found to be around 20 wt % CB, and an electrical network formed by conductive CB was proven by scanning electron microscopy investigation. Dielectric responses depicted an interfacial relaxation peak at 20 wt % CB content. LDPE/CB composites showed an electric field-dependent conductivity as and a hysteresis behavior around the percolation threshold region. The CB particles with high thermal conductivity increased the heat conductance of the LDPE/CB20 up to 56%. The dynamic mechanical analysis of the LDPE/CB composites exhibited a noticeable contribution of CB throughout the composites, increasing the storage and loss modulus. The physical interactions between CB particles in the filler network enhanced the thermal degradation of the LDPE/CB25 composite for more than 76°C. The maximum breakdown strength of the LDPE/CB composites appeared with an approximately 10% improvement for LDPE/CB5 than pure LDPE. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47043.     

Electrical and mechanical properties of some polymeric composites

Two unsaturated polyester resins based on poly[propylene‐phthalate‐hexane‐maleate] (PE1) and poly[oxydiethylene‐phthalate‐hexane‐maleate] (PE2) were prepared and crosslinked with styrene monomer. The structure of the prepared polyesters was detected using IR and NMR. The thermal behavior of the styrenated polyesters was determined using differential scanning calorimetry. The dielectric properties for the PE1 and PE2 styrenated polyesters and their mixtures with different ratios were also studied with a frequency range of 100 Hz to 100 kHz at room temperature (≈25°C). The mixture containing a 50/50 ratio of PE1/PE2 possessed the most promising dielectric properties. Thus, this sample was chosen along with the two separate styrenated polyesters to be loaded with three different types of fillers: calcium carbonate, clay, and quartz. This investigation led to the conclusion that the sample containing 50/50 PE1/PE2 loaded with 60–70% clay possessed the most promising dielectric properties. The compressive and tensile strength values were also studied for PE1, PE2, and their 50/50 mixture filled with the three types of fillers with the recommended concentrations (60 and 70%). The results indicated that the quartz composite (60%) had the best mechanical properties with respect to the clay and calcium carbonate. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1167–1180, 2002     

Electrical Resistivity of Composites

Percolation and Bruggeman's effective media theories, as they apply to the electrical conductivity of composites, are reviewed, and a general effective media (GEM) equation, which combines most aspects of both percolation and effective media theories, is introduced. It is then shown that the GEM equation quantitatively fits electrical resistivity (conductivity) as a function of the volume fraction data for binary composites. The parameters used to fit the experimental data are the electrical resistivities of the two phases, the percolation threshold for the lower resistivity phase (ô _c ), and an exponent t. Preliminary work, showing how the GEM equation can be used to model the piezoresistivity of composites by postulating that ô _c is a function of the independent variable, is also presented.     

新型炭黑填充抗静电和导电聚丙烯复合材料

以炭黑为导电填料,在聚丙烯中加入适量的环氧树脂和玻璃纤维,制备了新型的抗静电和导电聚丙烯复合材料。测定了不同复合体系的渗滤阈值,用扫描电镜(SEM)对相形貌进行了观察,并研究了环氧树脂和玻璃纤维用量对体积电阻率的影响。SEM照片表明在新型复合材料中,炭黑优先分布在环氧树脂中,环氧树脂包覆在玻璃纤维表面,通过玻璃纤维间的搭接形成导电通路。这种独特的结构使该复合材料的渗滤阈值低于聚丙烯/炭黑和聚丙烯/环氧树脂/炭黑复合体系的渗滤阈值。玻璃纤维和环氧树脂含量分别需要达到约10%,复合材料才能具有抗静电和导电作用。     

A representative and comprehensive review of the electrical and thermal properties of polymer composites with carbon nanotube and other nanoparticle fillers

In this review we present the results of our literature investigation into the electrical and thermal properties of carbon nanotube polymer composites. A short selection of data relating to conductive polymer composites with various fillers is provided for comparison. The effects of filler properties such as type and size, the use of hybrid fillers, fabrication methods for polymer composites and the importance of the modeling of the electronic and thermal transport mechanisms are discussed, as are more general factors influencing the properties of these composites. This review represents a comprehensive survey and constructive study and should serve as a useful reference tool for industrial and academic researchers working in this field. © 2017 Society of Chemical Industry     

Stretching‐induced percolation in polyvinylidene fluoride and nickel composites

To investigate the stretching effect of polymer‐based composites, the films of polyvinylidene fluoride (PVDF) and nickel (Ni) composites were stretched at 120°C. It was found there was an abrupt increase in dielectric constants and conductivities with stretching ratio (SR). In comparison to percolation effect caused by involvement of conductive particles, it was named as stretching‐induced percolation here. When SR was near the threshold, dielectric constants showed 17 times improvement and conductivities displayed four to five orders of magnitude enhancement at 100 Hz in low Ni fraction composites. And the reasons of stretching‐induced percolation were analyzed here. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

A modified model of electrical conduction for carbon black–polymer composites

A modified model of electrical conduction for carbon black‐polymer composites is proposed based on the general effective media theory and the number of carbon black particles per aggregate to describe their nonlinear conductive behavior. In order to consider the interactions between carbon black particles, a simple self‐consistent approach is used to improve the model. Expressions of electrical conductivity and percolation threshold are derived from the modified model. The predicted results of electrical conductivity and percolation threshold are in good agreement with experimental data reported in previous literature. Moreover, the dependences of electrical conductivity and percolation threshold on the number of carbon black particles per aggregate are discussed. Copyright © 2010 Society of Chemical Industry     

Effect of strain on the properties of an ethylene–octene elastomer with conductive carbon fillers

Composites that incorporate a conductive filler into an ethylene–octene (EO) elastomer matrix were evaluated for DC electrical and mechanical properties. Comparing three types of fillers (carbon fiber, low structure carbon black, and high structure carbon black), it was found that the composite with high structure carbon black exhibited a combination of properties not generally achievable with this type of filler in an elastomeric matrix. A decrease in resistivity at low strains is unusual and has only been reported previously in a few instances. Reversibility in the resistivity upon cyclic deformation is a particularly unusual feature of EO with high structure carbon black. The mechanical and electrical performance of the high structure carbon black composites at high strains was also impressive. Mechanical reinforcement in accordance with the Guth model attested to good particle–matrix adhesion. The EO matrix also produced composites that retained the inherent high elongation of the unfilled elastomer even with the maximum amount of filler (30% by volume). The EO matrix with other conducting fillers did not exhibit the exceptional properties of EO with high structure carbon black. Composites with carbon fiber and low structure carbon black did not maintain good mechanical properties, generally exhibited an increase in resistivity with strain, and exhibited irreversible changes in both mechanical and electrical properties after extension to even low strains. An explanation of the unusual properties of EO with high structure carbon black required unique features of both filler and the matrix. The proposed model incorporates the multifunctional physical crosslinks of the EO matrix and dynamic filler–matrix bonds. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 894–905, 2000     

Electrical conductivity and electromagnetic interference shielding effectiveness of nano-structured carbon assisted poly(methyl methacrylate) nanocomposites

Nanostructured carbon-based polymeric nanocomposites are gaining research interest because of their cost-effectiveness, lightweight, and robust electromagnetic interference (EMI) shielding performance. Till now, it is a great challenge to design and fabricate highly scalable, cost-effective nanocomposites with superior EMI shielding performance. Herein, highly scalable EMI shielding material with tunable absorbing behaviors comprising of low-budget ketjen black (K-CB) reinforced poly(methyl methacrylate) (PMMA) nanocomposites have been prepared using simple solvent assisted solution mixing technique followed by hot compression technique. The morphological investigation revealed the homogeneous distribution of K-CB and strong interfacial interaction in PMMA matrix, which validated the strong reinforcement and other intriguing properties of the nanocomposites. The PMMA nanocomposites showed a low percolation threshold (2.79 wt%) and excellent electrical conductivity due to the formation of 3D conductive network like architecture within the polymer matrix. Specifically, the 10 wt% K-CB nanocomposite possessed a superior EMI shielding performance of about 28 dB for X-band frequency range. Further, a huge change in EMI shielding performance of PMMA nanocomposites is observed with varying thickness. The brand new K-CB decorated PMMA nanocomposites are expected to open the door for next-generation cost-effective EMI shielding materials for academic and industrial applications.     

Conductive network formation and electrical properties of poly(vinylidene fluoride)/multiwalled carbon nanotube composites: Percolation and dynamic percolation

Conductive network formation and its dynamic process for multiwalled carbon nanotubes (MWNTs) and carboxyl‐tethered MWNT (MWNT‐COOH) filled poly(vinylidene fluoride)(PVDF) systems were investigated. Based on real‐time tracing the variation of electrical resistivity of systems with isothermal treatment time, the conductive network formation was evaluated. It was found that the conductive network formation was temperature and time dependent. The percolation time, characterized at a certain annealing time where the electrical resistivity started to decrease drastically, decreased with the increase of the filler concentration or the annealing temperature. However, the values of the percolation time and the activation energy of conductive network formation for the PVDF/MWNT‐COOH system were higher than those of the PVDF/MWNT system, indicating that the interaction between MWNTs and PVDF molecules played an important role in the conductive network formation of the composites. Furthermore, a modified thermodynamic percolation model was proposed to predict the percolation time of PVDF/MWNT composites. It was found that the calculated results fit the experimental data very well. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Enhanced electrical properties by tuning the phase morphology of multiwalled carbon nanotube‐filled poly(ether ether ketone)/polyimide composites

A novel high‐performance material with enhanced electrical properties was obtained by tuning the phase morphology of poly(ether ether ketone) (PEEK)/thermoplastic polyimide (TPI)/multiwalled carbon nanotube (MWCNT) composites. MWCNTs were selectively located in the TPI phase due to discrepant affinity of MWCNTs between PEEK and TPI. The dependence of the electrical properties of the PEEK/TPI/MWCNT composites on the phase morphology was investigated by changing the PEEK/TPI ratio, and the maximum conductivity was achieved with a PEEK/TPI ratio of 50/50, which could be explained by the selective location of MWCNTs and the co‐continuous phase morphology of the composites. © 2015 Society of Chemical Industry