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     

Novel dielectric behaviors in PVDF‐based semiconductor composites

Composites of polyvinylidene fluoride (PVDF) filled with different conductive fillers as carbon black (CB), nickel (Ni), zinc (Zn), and tungsten (W), respectively, were prepared at same processing condition. The temperature dependence of dielectric behaviors of composites was studied at wide filler concentration and wide frequency ranges. Results show that there are giant dielectric constants as the concentration of filler is near the percolation threshold. The dielectric constants of all studied composites decrease slowly with increasing of frequency and rise gradually with increasing filler contents in the composites. Two relaxation peak regions of dielectric constant are observed from ?30 to 40°C and from 100 to 150°C, which can be attributed to the contribution of polar effect of PVDF. The CB filled PVDF (CB/PVDF) composites present a lower percolation threshold than other metallic‐filler filled PVDF composites. The maximal dielectric constant was found in the Ni filled PVDF (Ni/PVDF) composite. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Carbon black–filled immiscible blends of poly(vinylidene fluoride) and high density polyethylene: Electrical properties and morphology

The electrical conductivity, current-voltage characteristics and morphology of carbon black–filled immiscible blends of poly(vinylidene fluoride)(PVDF) and high density polyethylene (HDPF) were investigated. Carbon black (CB) had stronger affinity to HDPE than to PVDF, resulting in its selective localization in the HDPE phase. The CB content and PVDF/HDPE volume ratio were the two main factors influencing the electrical conductivity, current-voltage characteristics, and morphology. At a fixed PVDF/HDPE volume ratio of 1/1, a percolation threshold of 0.037 volume fraction of CB was observed, and that value was much lower than that for conventional CB-filled polymer composites. At a fixed CB content (10 wt% CB), a maximum electrical conductivity was observed at a PVDF/HDPE volume ratio of 2.75. An increase in CB content in the composites with a fixed PVDF/HDPE volume ratio (1/1) and an increase in PVDF content in composites with a fixed CB content (10 wt%) greatly decreased the domain size of the PVDF phase. A positive-temperature-coefficient effect was used to determine the location of CB in the blends.     

Correlating mechanical and electrical properties of filler‐loaded polyurethane fluoroelastomers: The influence of carbon black

The dynamic mechanical properties and electrical conductivity of a class of polyurethane fluoroelastomers filled with different carbon black types and loadings were investigated. In particular, finely structured and coarsely structured carbon blacks were considered. Dynamic mechanical analysis (DMA) on the unfilled fluoroelastomer confirmed the phase‐segregated nature of this copolymer. The dynamic mechanical behavior of elastomeric compounds reinforced with finely structured carbon black was found to be strongly influenced by the filler content above a threshold value. This behavior may be attributed to the formation of carbon black aggregates and three‐dimensional anisotropic structures at increasing filler loading. Such an effect was not observed in compounds filled with coarsely structured carbon black particles, which do not seem to form higher level structures. These observations were supported by calculations on the hydrodynamic effect of the filler on the storage modulus G′ of carbon black–loaded compounds. Electrochemical impedance spectroscopy measurements on filled fluoroelastomers revealed the presence of an electrical percolation threshold for finely structured carbon black–filled compounds that supports the hypothesis of the presence of a three‐dimensional anisotropic network forming at high filler loading. No percolation threshold was found in coarsely structured carbon black–filled compounds in accordance with DMA. These results can provide useful guidelines for the design of high‐performance carbon black–filled polyurethane fluoroelastomers. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

A study of the mechanical and electrical properties of a polymer/carbon black binder system used in battery electrodes

The effects of carbon black content and crosslinking on the mechanical and electrical properties of a fluorinated elastomer, FC2178 (Dyneon Corp., Oakdale, MN), poly(vinylidene fluoride‐co‐hexafluoropropylene), were investigated and compared to those of poly(vinylidene fluoride) (PVDF). Attention was given to changes in mechanical and electrical properties of the polymers when under cyclic deformation. To describe the mechanical properties of the carbon‐filled polymers in a way that is independent of the chemical details, two mechanical models were used to fit cyclic stress–strain experiments. The linear model was used to determine the effect of crosslinking on the mechanical properties of crosslinked FC2178 films. However, when carbon black was added to the polymer films, the linear model no longer fit the data well. In particular, the cyclic stress–strain curves for carbon‐filled polymers showed non‐linear regions and displayed the characteristic of ‘memory.’ A non‐linear element was added in parallel with the existing elements of the linear model to successfully describe the effects of the added carbon black. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1891–1899, 2003     

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     

Electrical and mechanical behavior of carbon black–filled poly(vinyl acetate) latex–based composites

The electrical and mechanical behaviors of carbon black‐filled. Poly(vinyl acetate) latex‐based polymer composites were examined. These composites were found to exhibit percolation thresholds in electrical conductivity near 2 vol% carbon black due to their segregated microstructures. Storage modulus and ultimate tensile strength (UTS) both exhibited discontinuities at 10 vol% carbon black, corresponding to a critical pigment volume concentration. Drying composites at 60°C rather than room temperature produced a higher percolation threshold and better mechanical properties at carbon black loadings above 10 vol% carbon black. A figure of merit was proposed to assess the balance of electrical conductivity, storage modulus and UTS. The figure of merit exhibited a peak value at 10 vol% for composites dried at room temperature and was shifted to higher carbon black concentrations when composites were dried at 60°C.     

Percolation phenomena in carbon black–filled polymeric concrete

Percolation in carbon black‐filled polymeric concrete, is discussed based on the measured changes in electrical conductivity and morphology of the composite at different concentrations of carbon black. The percolation threshold ranged between 6 and 7 wt% (based on resin weight) of carbon black. Above this concentration, the filler particles formed agglomerates in contact with each other, suggesting that the conduction process is nearly ohmic in nature. A power law predicted by percolation theory described the behavior of the conductivity as a function of carbon black content. Microscopic analysis showed the presence of a continuous structure formed by the polyester resin and carbon black, in which silica particles were embedded.     

VGCF填充PVDF/PMMA复合材料导电性能的研究

以气相生长碳纤维（VGCF）为导电填料,聚偏氟乙烯（PVDF）、聚甲基丙烯酸甲酯（PMMA）为基体制备复合型导电高分子材料。考察了填料用量、基体种类、配比以及PVDF结晶行为对复合材料导电性能的影响。结果表明,VGCF填充PMMA、PVDF、PVDF／PMMA（50／50）体系的渗滤阔值分别为5、4、3phr的填料用量。VGCF的加入会导致PVDF／PMMA体系发生微观相分离,而且VGCF会选择性富集在PVDF的非晶相中,所以PVDF／PMMA／VGCF体系的导电性呈现双重渗滤现象,该体系的体积电阻率不仅取决于富集相中VGCF的含量,而且还与PVDF相的连续性及其结晶行为密切相关。     

Effect of carbon black structure on low‐strain conductivity of polypropylene and low‐density polyethylene composites

The influences of carbon black (CB) structure on the percolation threshold, mechanical properties, and strain‐resistivity response of polymer composites are studied. Low‐density polyethylene (LDPE) and polypropylene (PP) samples were blended with five different types of CB differing in structure. Relatively low strains were studied; the maximum strain was 10%. It was found that the CB concentration for maximum strain‐sensitivity of the electrical conductivity is higher for low structure carbon blacks but is essentially independent of the CB structure for medium‐ to high‐structure carbon blacks. However, the composite containing the largest particle size carbon black clearly showed the highest strain‐sensitivity to electrical conduction. The mechanical properties and sensitivity of electrical resistivity to tensile strain of the filled composites examined in the study are also presented and discussed. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

聚偏氟乙烯-丙烯酸酯原位乳液聚合的研究

采用原位乳液聚合 ,将聚偏氟乙烯 (PVDF)溶解于丙烯酸酯单体中 ,以碳氟表面活性剂 (FC- 80 ,氟醚 )和碳氢表面活性剂 (SLS、OP - 10 )为乳化剂 ,合成了PVDF改性的聚丙烯酸酯乳液 ,乳液在六个月内无分层现象。并用偏光显微镜和示差量热扫描仪对涂膜的结晶行为和热行为进行了研究 ,结果表明 :聚丙烯酸酯破坏了聚偏氟乙烯的结晶性使得改性后的胶膜透明。     

Special electrical conductivity of carbon black‐filled two‐phased thermoplastic vulcanizates

The electrical properties of carbon black (CB)‐filled two‐phased thermoplastic vulcanizates (based on ethylene‐propylene‐diene copolymer and polypropylene, TPV) were investigated in this article. The results showed that the composites had a singularity in electrical conductivity compared with CB‐filled polypropylene composites. Both the loading of CB and the concentration of rubber phase in TPV had the remarkable effect on electrical property of composites. The rubber particles in TPV presented unique and competitive effects in constructing CB electrical conducting network, namely exclusion and block effects. The percolation threshold value of composites apparently decreased with rubber phase content. However, percolation behavior of composites was weakened when rubber phase content was very high. The percolation behavior of composites with loading of CB is weakened apparently by rubber particles. When annealing the composites in the melt state, the resistance‐time dependence of composites was strongly affected by the pressure of mold annealing. Although air aging had a negligible effect on the electrical properties, the microstructure of the CB/TPV composites had changed during air aging. CB/TPV composite only exhibited the negative temperature coefficient behavior even though the temperature was in the melting region of polypropylene, which was mainly attributed to the exclusive effect brought by the thermal expansion of rubber particles. The special electrical properties of CB/TPV can find potential application in many fields. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Elastomeric and electrically conductive materials on basis of thermoplastic elastomers and their controlled manufacturing

Abstract

The present work presents a possibility to produce a rubber elastic and electrically conductive polymer material on the basis of dynamic vulcanisates. Thanks to the specific morphology of dynamic vulcanisates and the non-uniform carbon black distribution, carbon black filled dynamic vulcanisates can exhibit a very low percolation threshold of ～4 wt-%. Keeping the carbon black content low, a broad spectrum of resistivity properties can be achieved by variation of material factors like type and content of rubber phase and filler, concentration of cross-linking agent and compatibiliser and technological factors like mixing time respectively. In comparison with thermoplastic elastomers on the basis of block copolymers dynamic vulcanisates show a distinct lower percolation threshold. Up to a carbon black content of ～10 wt-% the mechanical properties of carbon black filled dynamic vulcanisates are not negative influenced essentially. To characterise the development of the carbon black dispersion and distribution processes and the conductivity properties in an internal mixer, the method of online measured electrical conductivity is suited very well for carbon black containing rubber mixtures. It could be shown in pre-investigations that this method promises to be a very useful tool for monitoring the mixing processes of carbon black filled dynamic vulcanisates in continuous mixing processes by means of extruders too.     

Injection‐molded parts of polypropylene/multi‐wall carbon nanotubes composites with an electrically conductive tridimensional network

Polypropylene‐based composites filled with multi‐wall carbon nanotubes (MWCNTs), ranging from 1 to 6 wt%, were obtained by injection molding from a previous masterbatch compounded by twin‐screw extrusion (TSE). Resultant electrical percolation phenomenon was related to the ultrathin structure of the carbon‐based fillers and the high dispersion achieved in the thermoplastic matrix. In particular, conductivity experiments showed a threshold value of 3 wt% (1.3 vol%) of MWCNTs for percolation to occur. Electrical percolation was achieved as a result of the formation of an interconnected three‐dimensional structure compromising a top average inter‐nanotube distance of about 493 nm among isolated nanotubes in polypropylene. The current work is hoped to bear significance toward understanding of the electrical performance for industrial ultrathin carbon black‐based polyolefin composites. POLYM. COMPOS., 37:488–496, 2016. © 2014 Society of Plastics Engineers     

Reversible electrical behavior with strain for a carbon black‐filled rubber

Most unfilled elastomers exhibit a high electrical resistance. Fillers are usually added to elastomers to enhance their mechanical properties. Frequently the filler type used is an electrically conductive carbon black and the inclusion of such fillers reduces the resistivity of the elastomer compound. Previous work has shown that for elastomers containing high abrasion furnace, carbon black fillers such as N330 (or N300 series) at a volume fraction above the percolation threshold the resistivity changes with strain, the precise resistivity versus strain behavior being nonlinear and irreversible for conventional carbon black fillers. A strain‐measuring device, deriving strain directly from a measure of the resistivity, requires that the behavior be reversible and reproducible from cycle to cycle. This work presents the electrical resistivity behavior of a natural rubber (NR) compound filled with Printex XE2 carbon black. This type of filler has a significantly different morphology to the N300 series blacks examined previously. The Printex was incorporated into the rubber at a volume fraction above its percolation threshold and its behavior is contrasted to that observed with N300 series carbon black‐filled NR. Here, and for the first time, reversible electrical resistivity dependence with strain is reported for an elastomer filled with Printex XE2. This reversible behavior under strain opens up the possibility of applications, such as a flexible load sensor, pressure sensor, or switch. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

PVDF/炭黑导电复合材料的PTC性能研究

研究炭黑种类和用量及ＰＶＤＦ种类对ＰＶＤＦ／炭黑导电复合材料ＰＴＣ特性的影响。结果表明,大粒径、比表面积小的Ｎ７６５炭黑填充导电复合材料的ＰＴＣ性能较好,出现ＰＴＣ现象的炭黑用量范围大;随着ＰＶＤＦ分子量的增大,ＰＶＤＦ／Ｎ７６５炭黑导电复合材料出现最大ＰＴＣ强度的炭黑用量减少,最大ＰＴＣ强度也随之增大。     

Electrical and rheological percolation in poly(vinylidene fluoride)/multi‐walled carbon nanotube nanocomposites

Nanocomposites of poly(vinylidene fluoride) (PVDF) and multi‐walled carbon nanotubes (MWCNTs) were prepared through melt blending in a batch mixer (torque rheometer equipped with a mixing chamber). The morphology, rheological behavior and electrical conductivity were investigated through transmission electron microscopy, dynamic oscillatory rheometry and the two‐probe method. The nanocomposite with 0.5 wt% MWCNT content presented a uniform dispersion through the PVDF matrix, whereas that with 1 wt% started to present a percolated network. For the nanocomposites with 2 and 5 wt% MWCNTs the formation of this nanotube network was clearly evident. The electrical percolation threshold at room temperature found for this system was about 1.2 wt% MWCNTs. The rheological percolation threshold fitted from viscosity was about 1 wt%, while the threshold fitted from storage modulus was 0.9 wt%. Thus fewer nanotubes are needed to approach the rheological percolation threshold than the electrical percolation threshold. Copyright © 2010 Society of Chemical Industry     

Conductivity of polyolefins filled with high‐structure carbon black

The electrical conductivities of various polyolefins filled with a high‐structure carbon black (CB) were studied. Typical percolation behaviors were observed in all of the materials studied. At a critical CB content, which defined the percolation threshold, CB formed conductivity pathways, and resistivity fell sharply from a value characteristic of an insulator into the range of 10–100 Ω cm. The dependence of the percolation threshold on the matrix viscosity was understood in terms of competing effects on CB dispersion during blending and CB flocculation during compression molding. For the conditions used in this study, polypropylene with a melt flow index of about 50 was optimum. Flocculation in the quiescent melt was studied directly by atomic force microscopy. Conductivity pathways formed over time by CB agglomeration. The temperature dependence of the percolation time was described by an Arrhenius relationship. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1799–1805, 2005     

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     

Particle size distribution,mixing behavior,and mechanical properties of carbon black (high‐abrasion furnace)–filled powdered styrene butadiene rubber

High‐abrasion furnace black (HAF, grade N330)–filled powdered styrene butadiene rubber [P(SBR/HAF)] was prepared and the particle size distribution, mixing behavior in a laboratory mixer, and mechanical properties of P(SBR/HAF) were studied. A carbon black–rubber latex coagulation method was developed for preparing carbon black–filled free‐flowing, noncontact staining SBR powders, with particle diameter less than 0.9 mm, under the following conditions: carbon black content > 40 phr, emulsifier/carbon black ratio > 0.02, and coating resin content > 2.5 phr. Over the experimental range, the mixing torque τ_α of P(SBR/HAF) was not as sensitive to carbon black content and mixing temperature as that of HAF‐filled bale SBR (SBR/HAF), whereas the temperature build‐up ΔT showed little dependency on carbon black content. Compared with SBR/HAF, P(SBR/HAF) showed a 20–30% mixing energy reduction with high carbon black content (>30 phr), which confers to powdered SBR good prospects for internal mixing. Carbon black and the rubber matrix formed a macroscopic homogenization in P(SBR/HAF), and the incorporation step is not obvious in the internal mixing processing results in these special mixing behaviors of P(SBR/HAF). A novel mixing model of carbon black–filled powdered rubber, during the mixing process in an internal mixer, was proposed based on the special mixing behaviors. P(SBR/HAF) vulcanizate showed better mechanical properties than those of SBR/HAF, dependent primarily on the absence of free carbon black and a fine dispersion of filler on the rubber matrix attributed to the proper preparation conditions of noncontact staining carbon black–filled powdered SBR. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2494–2508, 2004