Carbon Black-filled Composites Research Articles

Investigation of the Dielectric Properties of Graphite and Carbon Black-Filled Composites as Electromagnetic Interference Shielding Coatings

The main purpose of electromagnetic interference (EMI) shielding coatings is the insulation of sensitive devices and protect people from electromagnetic field exposure due to its effects on the human body. This paper investigates the dielectric properties, and electromagnetic shielding performances of graphite and carbon black (CB) filled epoxy matrix composites produced by the mechanical mixing method. The sample compositions were created at rates ranging from 1 to 7 wt%. Samples were analyzed by Vector Network Analyzer (VNA) using the coaxial method in the range of 1–14 GHz, including L band, S band, C band, X band and partially Ku band. After determining the scattering parameters with VNA, AC conductivity, absorption, reflection and total shielding efficiency values were calculated. At high frequencies, almost all the samples showed higher AC conductivity. CB-filled samples show higher AC conductivity than graphite-filled samples. The total shielding efficiency (SET) of the graphite-added samples (19–21 dB) is slightly higher than the carbon black-added samples (8–17 dB). Distinct filling ratios in graphite-added samples result in closer shielding behavior in contrast to carbon black-added samples. However, higher shielding efficiency is observed as the CB filler ratio increases. The shielding efficiencies of the samples with both types of filling materials vary little depending on the frequency. Reflection is the main mechanism of the shielding efficiency, which constitutes the majority of total efficiency for all types of samples.

Effects of fillers on the hydrogen uptake and volume expansion of acrylonitrile butadiene rubber composites exposed to high pressure hydrogen: -Property of polymeric materials for high pressure hydrogen devices (3)-

To develop sealing materials for high-pressure hydrogen devices, the effects of filler type and amount on the hydrogen uptake and volume expansion of rubber composites were evaluated up to 90 MPa. The amount of hydrogen in the rubber matrix and carbon black was elucidated using nuclear magnetic resonance, and the hydrogen elimination behavior of the composites was analyzed by thermal desorption analyses. As hydrogen physically adsorbed on carbon black, the hydrogen uptake of carbon black-filled composites increased. The hydrogen uptake of the composites filled with nonabsorbent silica was smaller, depending on the weight fraction of silica. The ratio of volume expansion to the amount of hydrogen in the matrix of carbon black-filled composites was suppressed by the reinforcement effect of carbon black, which did not expand with hydrogen uptake. The suppression of silica-filled composites was limited by the volume fraction of silica.

Understanding the Coupling Effect between Lignin and Polybutadiene Elastomer

From an environmental and economic viewpoint, it is a win–win strategy to use materials obtained from renewable resources for the production of high-performance elastomer composites. Lignin, being a renewable biomass, was employed as a functional filler material to obtain an elastomer composite with a higher degree of mechanical performance. In the presence of a suitable coupling agent, an elevated temperature was preferred for the reactive mixing of lignin with polybutadiene rubber (BR). It is quite fascinating that the mechanical performance of this composite was comparable with carbon black-filled composites. The extraordinary reinforcing behavior of lignin in the BR matrix was understood by an available model of rubber reinforcement. In rubber composite preparation, the interfacial interaction between polybutadiene rubber and lignin in the presence of a coupling agent enabled the efficient dispersion of lignin into the rubber matrix, which is responsible for the excellent mechanical properties of the rubber composites. The rubber composites thus obtained may lead to the development of a sustainable and cost-effective end product with reliable performance. This novel approach could be implemented in other type of elastomeric materials, enabling a genuine pathway toward a sustainable globe.

Effect of Matrix Chemical Nature on the Properties of Composites for Microwave Absorbers

Virgin and carbon black-filled composites have been prepared using two completely different matrixes – natural rubber (a non-polar, crystallizing elastomer) and nitrile butadiene rubber (a polar, non-crystallizing elastomer). The investigations reported reveal how the chemical nature of the rubber matrixes affects the dielectric (dielectric permittivity and dielectric loss angle tangent) and microwave (reflection coefficient, electromagnetic attenuation and electromagnetic shielding) properties of the obtained materials. The effects observed have been explained by the fact that interface polarization, relaxation processes, wetting and distribution of the absorption active filler are strongly dependent on the matrix character. The chemical nature of the matrix used predetermines composites properties through the effects related to the mechanisms of dielectric losses and electromagnetic interaction. The results obtained allow an appropriate choice of elastomeric matrixes for the production of composites designed for microwave absorbers.

Dynamic Mechanical Properties of Soy Protein Filled Elastomers

Dynamic mechanical properties including temperature effect, stress softening, and Payne effect are studied on the elastomer composites filled with soy protein or carbon black. The comparison of protein composite with well-known carbon black composites provides further insight into the protein composites. The elastomers filled with soy protein aggregates give substantial reinforcement effect when compared with the unfilled elastomers. Approximately 400 times increase in shear elastic modulus was observed when 40% by weight of protein is incorporated into the elastomers. The sample films were cast from the particle dispersion of soy protein isolate and carboxylated styrene–butadiene latex. At the higher temperatures, the shear elastic modulus of soy protein-filled composites does not decrease as much as that of the carbon black-filled composites. The behavior of elastic and loss modulus under the oscillatory strain of different magnitude is similar to that of carbon black reinforced styrene–butadiene rubber. However, carbon black composites show a better recovery behavior after eight cycles of dynamic strain. The reduction of shear elastic modulus with dynamic strain (Payne effect) was compared with Kraus model and the fitting parameter related to the aggregate structure of the soy protein. A reasonable agreement between the theoretical model and experiment was obtained, indicating the Payne effect of the protein-related network structure in the elastomers could also be described by the kinetic agglomeration de-agglomeration mechanism.

Comparison of PVDF and PVDF-TFE-P as Binders for Electrode Materials Showing Large Volume Changes in Lithium-Ion Batteries

The mechanical and electrical properties of a terpolymer, poly(vinylidene fluoride-tetrafluoroethylene-propylene) (PVDF-TFE-P, BRE-7131X, Dyneon Corp.) and its carbon black-filled composites (without active anode material) have been investigated carefully and are compared to those of PVDF (Solef 1008). High capacity anode materials such as a-Si and have up to 250% volumetric changes during charge/discharge cycling which challenges the mechanical properties of standard binders used in Li-ion battery electrodes. The measurements were carried out on dry polymer films and on films immersed in a nonaqueous solvent commonly used in Li-ion cells (ethylene carbonate/diethyl carbonate, EC/DEC, 1:2 by volume). PVDF and its carbon-filled composites show a maximum elongation before break of less than 10%. However, triethylenetetramine crosslinked BRE-7131X and its carbon-filled composites can be stretched to more than 100% strain before breaking in air and in EC/DEC (1:2 by volume). Furthermore, the stress and the resistivity of the carbon-filled crosslinked BRE-7131X films changes reversibly during elongation/contraction cycles. © 2003 The Electrochemical Society. All rights reserved.

Conductive nitrile rubber composite containing carbon fillers: Studies on mechanical properties and electrical conductivity

The effect of type and proportion of conductive carbon filler on the mechanical properties and electrical conductivity of nitrile rubber (NBR) composites containing particulate carbon black (Conductex 900) and short carbon fibres (SCF) has been studied. The SCF-filled composites had poorer mechanical properties than the carbon black-filled composites because of the lower degree of interaction between the carbon fibres and the rubber matrix. On increasing the proportion of filler in both types of composite, the resistivity was observed to drop by several orders of magnitude at a critical filler concentration region which was lower for SCF-filled composites than for carbon black-filled composites. Conduction through the composites is explained on the basis of the formation of a continuous conductive network and a transport mechanism involving the tunnelling of electrons across the gaps between two discontinuous conducting elements. Experimental and calculated values of electrical resistivity show close similarity only at higher filler loadings.

Electromagnetic Interference Shielding by Conductive Nitrile Rubber Composites Containing Carbon Fillers

Electromagnetic interference (EMI) shielding characteristics of nitrile rubber composites filled with short-carbon fibre (SCF), conductive car bon black (Conductex™ 900), and filler blend (SCF + Conductex™ 900) have been studied. The measurements of shielding effectiveness (SE) were carried out in two different frequency ranges-200-1000 MHz and 8-12 GHz (X-band range). It has been observed that the SE of the composites is frequency depen dent, especially at the higher frequency range, and it increases with increasing frequency. The increase of filler loading also enhances the SE of the composites. The SCF-filled composites register higher SE compared to that of filler blend or purely carbon black-filled composites. The correlation between SE and bulk conductivity of various composites is also discussed. The results indicate that the composites having higher fibre loading (loading > 30 phr) can be used for the purpose of EMI shielding, as well as for some microwave applications.