Electrical Properties and EMI Shielding

Carbon fillers have lower density compared to metal powders. Also, they are more inert and compatible with most of the polymers than are the metal powders 

The effects of carbon-based nanofillers of EG, MWCNTs, and CNFs on the AC conductivity and dielectric constant of elastomeric grade EVA (50% vinyl acetate content) at a particular frequency of 12 Hz, are shown in Fig. 29a, b [194]. EVA-EG, EVA-T, and EVA-F represent EVA-based nanocomposites reinforced with EG, MWCNT, and CNF respectively. 

EVA shows a percolation threshold after the addition of 8.2 vol% CNF, whereas a higher amount of EG (10.9 vol%) is required to reach percolation. MWCNT exhibits a percolation at 10.0 vol% and shows an increase of five orders of magnitude as 

The optimum filler loading of CNFs for SE (34.4 dB at 12 GHz) is 16 wt%. This result is very much comparable with the values reported by Zhang et al. [197]. The target value of the EMI SE for commercial applications is in the range of 10-20 dB [197]. Even a minimum addition of 4 wt% CNF provides sufficient SE. With a SE of 10-20 dB, a sample can block 90-99% of the incident electromagnetic signals [197, 198]. 

It is well established that the SE of a conductive composite is related to its conductivity. The interconnected CNF networks within the composite establish the electrical conduction pathway, leading to good electrical properties and SE. The correlation between the SE and electrical conductivity of EVA-F composites is displayed in Fig. 30b [196]. 

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P. Saini, V. Choudhary, S. K. Dhawan, Electrical Properties and EMI Shielding Behavior of Highly Thermally Stable Polyanihne/Colloidal Graphite Composites. Polym Adv Technol 2009,20,355-361. 

Im J S, Kim J G and Lee Y S (2009) Fluorination effects of carbon black additives for electrical properties and EMI shielding efficiency by improved dispersion and adhesion, Carbon 47 2640-2647. 

Figure 11.1. Carbon black additives can also conduct electricity, offering a simple and effective means of providing antistatic properties or EMI shielding. ( Photograph Cabot Corporation)...

A significant use of acetylene black is in dry cell batteries where it contributes low electrical resistance and high capacity. In rubber it gives electrically conductive properties to heater pads, tapes, antistatic belt drives, conveyor belts, and shoe soles. It is also useful in electrically conductive plastics such as electrical magnetic interference (EMI) shielding enclosures. Its contribution to thermal conductivity has been useful in rubber curing bags for tire manufacture. 

CPCs can find many applications such as sensors, EMI shielding, stretchable conductor, and thermoelectric materials based on their excellent electrical properties and other unique physical characteristics. In this section, some application cases are presented and the property requirements of CPCs-based specific electrical application are discussed, most of which greatly associate with conductive network strucmre in CPCs. 

So far as electrical properties are concerned CNT-PMMA composites have shown lot of promise as an effective EMI shielding material at very low loadings together with improved mechanical strength. In conclusion, significant progress has been made in the processing of CNT-PMMA composites and the efforts should be made to push these composites for commercial applications. The sectors such as aerospace, automobile, sports can benefit most from these composites. 

One single property of filler - electric conductivity - affects many properties of the final products. These properties include electric insulation, conductivity, superconductivity, EMI shielding, ESD protection, dirt pickup, static decay, antistatic properties, electrocatafysis, ionic conductivity, photoconductivity, electromechanical properties, thermo-electric conductivity, electric heating, paintability, biocompati-bilify, etc. Possession of one of these properties in a polymer can make it useful in industiy and eveiyday use. Examples are given in Chapter 19. Here, the electrical... 

The fabrication and electrical properties of carbon nanofiber-polystyrene composites and their potential applications for EMI shielding have been reported [42]. Being lightweight is a key technological requirement for the development of practical EMI shielding systems. Thus the fabrication of foam structures to further reduce the weight of carbon nonofiber-ploymer composites has been recently demonstrated and simple preparation routine has been reported [43] by which this novel foam structure can be prepared. 

Reasons for use abrasion resistance, cost reduction, electric conductivity (metal fibers, carbon fibers, carbon black), EMI shielding (metal and carbon fibers), electric resistivity (mica), flame retarding properties (aluminum hydroxide, antimony trioxide, magnesium hydroxide), impact resistance improvement (small particle size calcium carbonate), improvement of radiation stability (zeolite), increase of density, increase of flexural modulus, impact strength, and stiffness (talc), nucleating agent for bubble formation, permeability (mica), smoke suppression (magnesium hydroxide), thermal stabilization (calcium carbonate), wear resistance (aluminum oxide, silica carbide, wollastonite)... 

In many applications, moderate to high electrical conduction is required to serve the purpose. In such systems, it is preferred to prepare ICPs-based BLNs or CMPs/NCs/HYBs by incorporation of highly doped forms (or ICPs) inside a variety of polymeric hosts (thermoplasts, thermosets, rubber, elastomer). Many a times, ICPs-based copolymers have also been made to optimize the conductivity, processability, electroactivity, and optoelectronic properties. These copolymers are widely employed in the areas like corrosion inhibition, EMI shielding, ECs, gas sensing, biosensing, energy storage, thermoelectric, antistatics, etc. 

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