The conductivity behavior of multi‐component epoxy,metal particle,carbon black,carbon fibril composites

Following the previous studies of epoxy/silver conductive composites, a detailed investigation of the influence of ethylene glycol on the resulting resistivity of various composites was carried out. Ethylene glycol was found to have a catalytic effect on the curing process of the epoxy resin, verified by differential scanning calorimetry studies. The accelerated curing process diminishes settling of the metal particles and therefore results in better and more uniform conductivities. High temperature curing of the composites was found to have a similar effect on the conductivity. The conductivity behavior of some other composites, such as epoxy/nickel, epoxy/nickel/carbon fibrils, and epoxy/carbon black/carbon fibrils, were also studied. The structure–property relations were better understood through scanning electron microscopy observations. Silver and nickel particles were found to perform differently in the cured epoxy, showing different percolation concentrations and conductivity levels. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1706–1713, 2002     

Electrical conductivity of epoxy/silicone/carbon black composites: Effect of composite microstructure

The objective of this work is to study the effect of electrical conductivity and physical‐mechanical properties of carbon black (CB) filled polymer composites. This goal is achieved by synthesizing epoxy/silicon phase separated blend structure of composites filled with CB. The percolation threshold of epoxy/silicone/CB composites decreased and the total conductivity increased compared to the pure epoxy/CB composite. A threefold increase was obtained with tensile strength of epoxy/silicone/CB composite with 25 wt% of silicone and 5 wt% of CB in comparison with epoxy/CB systems. This composite has conductivity of about 10⁻⁶ S/cm, which is six orders of magnitude higher than for epoxy/CB composites at the same concentration of CB. POLYM. COMPOS., 35:2234–2240, 2014. © 2014 Society of Plastics Engineers     

Effect of carbon black on electrical property of graphite nanoplatelets/epoxy resin composites

Epoxy/graphite nanoplatelets (GNPs)/carbon black (CB) composites were prepared by liquid mixing method. The morphologies and microstructures of the composites were examined by scanning electron microscope and X‐ray diffraction. The results indicated that CB can improve effectively the dispersion of GNPs and form excellent conductive network in the matrix. When the weight ratio of GNPs to CB was 9:1 (total filler content was 1 wt%), the conductivity of the composite was three orders of magnitude higher than that of composites with GNPs alone (1 wt%). The percolation threshold of GNPs_0.9CB_0.1/epoxy resin composites was 0.5 wt. %, which was lower than that of composites with GNPs alone (1 wt%). The mechanism for the effect of CB on electrical property of GNPs/epoxy resin composites was also investigated. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers.     

Effect of nanoclay on positive temperature coefficient to resistivity characteristics of high density polyethylene/silver‐coated glass bead composites

Positive temperature coefficient to resistivity characteristics of high density polyethylene (HDPE)/silver (Ag)‐coated glass bead (45 wt%) composites, without and with nanoclay, has been investigated with reference to HDPE/carbon black (CB) (10 wt%) composites. Plot of resistivity versus temperature of HDPE/CB (10 wt%) composites showed a sudden rise in resistivity (PTC trip) at ≈128°C, close to the melting temperature (T_m) of HDPE. However, for HDPE/Ag coated glass bead (45 wt%) composites, the PTC trip temperature (≈88°C) appeared well below the T_m of HDPE. Addition of 1 phr clay in the composites resulted in an increase in PTC trip temperature of HDPE/Ag‐coated glass bead (45 wt%) composites, whereas no significant effect of clay on PTC trip temperature was evident in HDPE/CB/clay composites. We proposed that the PTC trip temperature in HDPE/Ag‐coated glass bead composites was governed by the difference in coefficient of thermal expansion of HDPE and Ag‐coated glass beads. The room temperature resistivity and PTC trip temperature of HDPE/Ag‐coated glass bead (45 wt%) composites were found to be very stable on thermal cycling. Dynamic mechanical analyzer results showed higher storage modulus of HDPE/Ag‐coated glass bead (45 wt%) composites compared with the HDPE/CB (10 wt%) composites. Thermal stability of HDPE/Ag‐coated glass bead (45 wt%) composites was also improved compared with that of HDPE/CB (10 wt%) composites. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Epoxy resin/plasticized carbon black composites. Part I. Electrical and thermal properties and their applications

The development of conductive polymer composites remains an important endeavor in light of growing energy concerns. A conducting polymer composite in the presence of plasticized carbon black (CB) and epoxy resin has been developed. Room temperature electrical conductivity, mobility carriers (μ), and number of charges (N) increase by increasing CB content. Electrical conductivity–temperature dependence of the composite was investigated and negative temperature coefficient of conductivity (NTC) behavior of the composites was revealed. The mechanism of the NTC effect in materials is related to the thermal expansion of the epoxy matrix and barriers height energy. The current–voltage behavior of epoxy/CB composites shows a switching effect and the mechanism of negative resistance is interpreted in details. Thermal conductivity (γ) increases with increasing filler content and the experimental data was compared with a theoretical model based on energy balance equation. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Sepiolite hybridized commercial fillers,and their effects on curing process,mechanical properties,thermal stability,and flammability of ethylene propylene diene monomer rubber composites

Ethylene propylene diene monomer rubber (EPDM)-based composites containing sepiolite (sep) hybridized with calcium carbonate (CaCO₃), silica (Sil) or carbon black (CB) were prepared on a two-roll mill. The influence of fillers’ contents on the curing, mechanical, thermal and flammability of the composites was investigated. In comparison with EPDM/sep at 30 parts per hundred rubbers (phr) as a control composite, EPDM/sep/CB composites exhibited an outstanding improvement in tensile strength followed by EPDM/sep/Sil and EPDM/sep/CaCO₃ composites. EPDM/sep/CB displayed the highest thermal stability and also improved flammability resistance. In addition, a higher amount of carbon black gave higher tensile strength. The results were influenced by the ability of CB to disperse well and form protective layers acting as mass transport barriers in the matrix. The field emission scanning electron microscopy analyses proved better dispersion of CB in the matrix. The presence of protective layers on the surface of samples consequently improved the thermal properties of the EPDM composites. The mechanism of formation of char protective layer in hybrid EPDM composites was also investigated based on morphological observations of char residues. According to this work, Sil and CB were able to hybrid with sep, while sep could be a potential substitution of CaCO₃ in the EPDM composites.     

Effect of nanosized carbon black on the morphology,transport, and mechanical properties of rubbery epoxy and silicone composites

Three different types of nanosized carbon black (CB), Printex XE2 (CBP), Vulcan XC72, and Printex 140 U (CBU), were dispersed by mechanical mixing in rubbery epoxy (RE) and silicone to produce composites. It was found that the maximum possible loading of CB in the polymers depended on the surface area of CB. For a given loading, all three CBs produced similar improvements in the thermal conductivity of the resulting composites, but their effects on the electrical conductivity varied and ranged from insulating composites with CBU to conducting composites with CBP. CBP produced a greater improvement in the electrical conductivity than the thermal conductivity of the polymers compared to the other CBs. This was attributed to the high structure of CBP, which led to the formation of a concatenated structure within the matrix. The CB/silicone composites had a similar thermal conductivity to that of the CB/RE composites, but only the CBP/silicone composite produced at 8 wt % loading was electrically conducting. The compression and hardness properties of RE were also significantly improved with the addition of CB. However, in the case of silicone, only CBP had a considerable effect on the compression properties. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

炭黑/环氧树脂复合材料导电行为的研究

分别采用不同的混合分散方法制备炭黑/环氧树脂(CB/EP)复合材料(CB牌号为F101、XE2,EP牌号为E-54、E-51和E-44),研究了制备工艺、CB用量和CB结构等对复合材料导电性能的影响。结果表明:不同方法制得的复合材料体积电阻率的大小依次为机械混炼法离心混合法超声分散法;CB/EP复合材料的导电性能随CB用量增加而显著提高,并且F101/E-54、XE2/E-54复合材料体系均表现出明显的导电渗流行为;CB结构对复合材料的导电性能影响较大,F101/E-54、XE2/E-54复合材料体系的导电渗流阈值分别为3.85%、0.47%。     

环氧树脂/镀银纳米石墨微片导热复合材料的制备与性能

以膨胀石墨为原料,采用超声分散法和化学镀法制得镀银纳米石墨微片,然后将其填充在环氧树脂基体中制备环氧树脂/镀银纳米石墨微片复合材料。结果表明,银粒子均匀镀覆在纳米石墨微片上,银层厚度为100 nm,有利于在环氧树脂基体中形成导热通路;与环氧树脂相比,环氧树脂/镀银纳米石墨微片复合材料的力学性能和热导率能都得到提高;当镀银纳米石墨微片含量为3 %时,复合材料的热导率为1.827 W/(m·K),比纯环氧树脂热导率提高了近5倍。     

New antistatic charge and electromagnetic shielding effectiveness from conductive epoxy resin/plasticized carbon black composites

Recently, there is an increasing interest in electromagnetic interference shielding due to the rapid increase in electromagnetic pollution and the wide use of commercial and military products. Conducting polymer composites were prepared in the presence of epoxy resin and plasticized carbon black (CB). The structural characteristics of the composites were examined by means of scanning electron microscopy, cross linking density, and interparticle distance among conductive particles. The mechanical properties such as Young's modulus, elongation at break, and hardness of the composites were investigated as a function of CB content. The results indicated that CB could improve the composite microstructure. The higher mechanical behavior than green epoxy can be attributed to the interaction between CB particles and epoxy resin. The conductivity, mobility carriers, and number of charges of the composites at room temperature were found to be dependent on CB content. The applicability of the composites to antistatic charge dissipation was examined. Dependence of the microwave properties of the epoxy/CB composites on the volume fraction of CB particles and frequency were studied. Moreover the permittivity as a function of frequency of the composites was studied. The electromagnetic wave shielding of epoxy/CB composites is dominant by both reflection and absorption. Composites can find applications in antistatic charge dissipation and in suppression of electromagnetic interference and stealth technology. POLYM. COMPOS., 2008. © 2007 Society of Plastics Engineers     

聚醚酰亚胺对炭黑填充环氧树脂复合材料导电性能和吸波性能的影响

利用反应诱导方法设计制备了炭黑(CB)包覆环氧树脂(EP)微球/聚醚酰亚胺(PEI)(EP/PEI/CB)复合材料。研究了该复合材料的微观结构,测量了其导电性能及在Ka波段的吸波性能,并与CB填充EP(EP/CB)复合材料进行了对比。结果表明,在EP/PEI/CB中,CB选择性分布在PEI相中并形成较规则的立体网状连续相,EP为30μm左右大小的微球分散相,与EP/CB相比具有更低的体积电阻率。EP/PEI/CB属于一种谐振腔式吸波体,在33～40 GHz范围具有较好的吸波性能且优于EP/CB,最大吸收峰出现在35.61 GHz,峰值反射率(R)为–17.40 dB,吸收带宽3.22 GHz(R–10 dB).     

Electrical properties and morphology of polypropylene/epoxy/glass fiber composites filled with carbon black

The volume resistivity and percolation thresholds of carbon black (CB) filled polypropylene (PP), PP/epoxy, and PP/epoxy/glass fiber (GF) composites were measured. The morphology of these conductive polymer composites was studied with scanning electron microscopy (SEM). The effects of the GF and epoxy contents on the volume resistivity were also investigated. The PP/epoxy/GF/CB composite exhibited a reduced percolation threshold, in comparison with that of the PP/CB and PP/epoxy/CB composites. At a given CB content, the PP/epoxy/GF/CB composite had a lower volume resistivity than the PP/CB and PP/epoxy/CB composites. SEM micrographs showed that CB aggregates formed chainlike structures and dispersed homogeneously within the PP matrix. The addition of the epoxy resin to PP resulted in the preferential location of CB in epoxy, whereas in the PP/epoxy/GF multiphase blends, because of the good affinity of CB to epoxy and of epoxy to GF, CB particles were located in the epoxy phase coated on GF. The decreased percolation threshold and volume resistivity indicated that conductive paths existed in the PP/epoxy/GF/CB composite. The conductive paths were probably formed through the interconnection of GF. Appropriate amounts of GF and epoxy should be used to decrease the volume resistivity and provide sufficient epoxy coating. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1142–1149, 2005     

The influence of synergistic stabilization of carbon black and clay on the electrical and mechanical properties of epoxy composites

Studies of acetone-based suspensions suggest a synergistic stabilization of clay by carbon black (CB) that involves a haloing effect (i.e., CB surrounding clay). This unique microstructural development ultimately influences the electrical and mechanical properties of epoxy composites that contain both particles. With the addition of 0.5 wt.% clay, electrical conductivity increases by an order of magnitude for CB filled epoxy (relative to composites containing no clay), but no significant improvement is observed in storage modulus. Composites containing equal concentrations of CB and clay show reduced electrical conductivity, but significant improvement in storage modulus (relative to the composites containing equal amount (wt.%) of either CB or clay alone). Both electrical conductivity and storage modulus improve in composites containing a 1:2 clay:CB (wt/wt) ratio. This synergy between CB and clay is a useful tool for simultaneously improving the electrical and mechanical properties of solution-processed composites.     

Biphenyl liquid crystal epoxy containing flexible chain: Synthesis and thermal properties

A biphenyl type liquid crystal epoxy (LCE) monomer 4,4′-di(2,3-epoxyhexyloxy)biphenyl (LCBP4) containing flexible chain was synthesized and the curing behavior was investigated using 4,4′-diaminodiphenylmethane (DDM) as the curing agent. The effect of curing condition on the formation of the liquid crystalline phase was examined. The cured samples show good mechanical properties and thermal stabilities. Moreover, the relationship between thermal conductivity and structure of liquid crystalline domain was also discussed. The samples show high thermal conductivity up to 0.28–0.31 W/(m*K), which is 1.5 times as high as that of conventional epoxy systems. In addition, thermal conductive filler, Al₂O₃, was introduced into LCBP4/DDM to obtain higher thermal conductive composites. When the content of Al₂O₃ was 80 wt%, the thermal conductivity of the composite reached to 1.86 W/(m*K), while that of diglycidyl ether of bisphenol A (Bis-A) epoxy resin/DDM/Al₂O₃ was 1.15 W/(m*K). Compared with Bis-A epoxy resin, the formation of liquid crystal domains in the cured LCE resin enhanced the thermal conductivity synergistically with the presence of Al₂O₃. Furthermore, the introduction of Al₂O₃ also slightly increased the thermal stabilities of the cured LCE.     

Crystallization behavior of carbon black‐filled polypropylene and polypropylene/epoxy composites

The crystallization behavior of polypropylene (PP)/carbon black (CB) and PP/epoxy/CB composites was studied with differential scanning calorimetry (DSC). The effects of compatibilizer MAH‐g‐PP and dynamic cure on the crystallization behavior are investigated. The nonisothermal crystallization parameters analysis showed that CB particles in the PP/CB composites and the dispersed epoxy particles in the PP/epoxy composites could act as nucleating agents, accelerating the crystallization of the composites. Morphological studies indicated that the incorporation of CB into PP/epoxy resulted in its preferential localization in the epoxy resin phase, changing the spherical epoxy particles into elongated structure, and thus reduced the nucleation effect of epoxy particles. Addition of MAH‐g‐PP significantly decreased the average diameter of epoxy particles in the PP/epoxy and PP/epoxy/CB composites, promoting the crystallization of PP more effectively. The isothermal crystallization kinetics and thermodynamics of the PP/CB and PP/epoxy/CB composites were studied with the Avrami equation and Hoffman theory, respectively. The Avrami exponent and the crystallization rate of the PP/CB composites were higher than those of PP, and the free energy of chain folding for PP crystallization decreased with increasing CB content. Addition of MAH‐g‐PP into the PP/epoxy and PP/epoxy/CB composites increased the crystallization rate of the composites and decreased the chain folding energy significantly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 104–118, 2006     

功能化碳纳米管/环氧树脂多孔复合材料制备及电磁屏蔽性能

以马来酸酐（MA）为功能性单体,通过自由基反应制备了马来酸酐功能化的多壁碳纳米管（MA-MWCNT）;以MA-MWCNT、环氧树脂、蓖麻油酸改性的四乙烯五胺固化剂、釉粉、水为原料,通过悬浮乳液聚合法制备了功能化碳纳米管/环氧树脂多孔复合材料。采用拉曼光谱、X射线衍射、红外光谱、X射线光电子能谱对功能化的碳纳米管进行了表征和测试。采用扫描电镜（SEM）、表面电阻测量仪、矢量网络分析仪对复合材料的表面形貌、电导率和电磁屏蔽性能进行了测试。结果表明：马来酸酐功能化单体的引入能够很好地改善碳纳米管的分散性能及材料的电磁屏蔽性能;随着碳纳米管含量的增多,复合材料的电导率增大,电磁屏蔽效能峰值增大,材料的电磁屏蔽性能增强;加入功能化的碳纳米管比加入未功能化碳纳米管的电磁屏蔽性能高,多孔复合材料比无孔复合材料的电磁屏蔽性能高。当加入功能化的碳纳米管的量为3%时,制备得到的多孔材料电磁屏蔽性能最佳,其电磁屏蔽性能峰值达到31.1dB。     

Dispersion,Mechanical and Thermal Properties of Epoxy Resin Composites Filled with the Nanometer Carbon Black

The nanometer carbon black (CB) was employed to prepare epoxy resin/carbon black (EP/CB) composites by blending-casting method. The different modified methods of silicone coupling agent were used to improve the dispersion of CB in epoxy resin. The mechanical and thermal properties of EP/CB composites were investigated. Experimental results showed that the mechanical properties increased at first, but decreased with excessive addition of CB. When the mass fraction of CB was 2%, the mechanical properties were maximum. The use of modified CB significantly enhanced the mechanical properties of the composites. For given CB loading, the CB modified by pretreatment method displayed better dispersion in the epoxy resin than that of the direct mixing method. SEM observation revealed that the tensile fracture surface of the composite filled with 2 wt% modified CB held more microcracks than that of 5 wt% modified CB, and the formed microcracks could consume more energy of rupture, finally to have better tensile strength. DSC analysis showed that the glass transition temperature (Tg) of the composites increased with the increasing mass fraction of CB.     

Effect of acrylic copolymer dispersants bearing epoxy groups on rheological and dielectric properties of carbon black‐filled epoxy system

In this article, the use of copolymeric dispersants with an acrylic backbone and epoxy side groups for formulating carbon black (CB)‐epoxy composites are described. Six epoxy‐containing acrylic copolymer dispersants were prepared from hexyl methacrylate (HMA), poly(ethylene glycol) ethyl ether methacrylate (PEGMA), and glycidyl methacrylate via a group transfer polymerization technique. The epoxy‐containing acrylic copolymer of the highest concentration of PEGMA showed a desirable passivation effect on CB, and was found to lower the viscosity of the CB‐epoxy paste, leading to the well‐cured composite after heat treatment. The thick composite film prepared by employing the [CB/acrylic dispersant/epoxy] paste was built up on a Cu plate by a screen printing process followed by thermal curing. The dielectric properties of the 3.1 vol % CB‐filled epoxy film showed us high dielectric constant (Dk 4900) and rather low dissipation factor (Df 29%) at 1 MHz. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Novel Ag/C nanocable/epoxy resin composite

Silver/carbon (Ag/C) nanocables were obtained in the presence of cetyltrimethylammonium bromide (CTAB) under hydrothermal conditions in order to modify epoxy resin. Nanocable is a nanocomposite of nanowire (core) wrapped with one or more outer layers (shell). Scanning electron microscopy and energy‐dispersive X‐ray spectroscopy proved that nanocables consist of a silver nanowire core and a carbon outer shell. The (Ag/C)/epoxy composites were prepared by compounding Ag/C nanocables and epoxy resin. An investigation of the thermal, mechanical, and dielectric properties of these composites showed that the thermal stability and dielectric constant of the composites were enhanced. Interestingly, the breakdown strength of the composites at room temperature increased. Normally, breakdown strength decreases when conducting fillers are added. Fracture morphology of the (Ag/C)/epoxy composite also showed increased toughness. The relationship between the properties and microstructure of the composite was discussed in detail to explain the mechanism behind the change in material properties. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Highly reversible and repeatable PTCR characteristics of PMMA/Ag‐coated glass bead composites based on CTE mismatch phenomena

Positive temperature coefficient of resistivity (PTCR) behavior of poly(methyl methacrylate) PMMA/silver (Ag)‐coated glass bead composites has been investigated with reference to the conventional PMMA/carbon black (CB) composites. The PMMA/CB composites showed a sudden rise in resistivity (PTC trip) at 115°C, close to the glass transition temperature (T _g, 113°C) of the PMMA. However, the PTC trip temperature (92°C) of PMMA/Ag‐coated glass bead composites was appeared well below the T _g of PMMA. The room temperature resistivity and PTC trip temperature of the composites were also very much stable upon thermal cycling. Addition of 1 phr of nanoclay increased the PTC trip temperature of PMMA/CB composites to 120°C, close to the T _g (118°C) of PMMA/clay nanocomposites, while PMMA/clay/Ag‐coated glass bead nanocomposites showed the PTC trip at 98°C. We proposed that the mismatch in coefficient of thermal expansion (CTE) between PMMA and glass beads played a key role that led to a disruption in continuous network structure of Ag‐coated glass beads even at a temperature well below the T _g of PMMA. The decrease in dielectric permittivity of PMMA/Ag‐coated glass bead composites on increasing frequency indicated possible use of the PTC composites as dielectric material. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers