Optimization of the Electrical Conductivity of ABS Nanocomposites filled with Carbon Black and Carbon Nanotubes
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Optimization of the Electrical Conductivity of ABS Nanocomposites filled with Carbon Black and Carbon Nanotubes Shantanu Talapatra and Rosario A. Gerhardt School of Materials Science and Engineering, Georgia Institute of Technology, 771 Ferst Drive, Atlanta, GA, 30332-0245
ABSTRACT Poly(acrylonitrile-co-butadiene-co-styrene) (ABS) is a thermoplastic polymer that is used in numerous structural applications as a result of its excellent mechanical properties. For those applications where good electrical conductivity is also desired, carbon black is often used as the filler of choice. Most reports in the literature indicate that at least 8 wt% carbon black filler is needed in order to achieve percolation. Our group recently reported that by manual mixing of ABS pellets and carbon black to create a segregated microstructure, percolation was achieved at an unprecedented low filler fraction of less than 0.01 wt% carbon black, a value which is comparable to or even better than that obtained using single wall carbon nanotubes as the filler. While the ABS/CB composites had excellent electrical performance, with a conductivity as high as 10-1 S/m, their mechanical strength was compromised. In this paper we report on new experiments designed to maintain high electrical conductivity while improving on the mechanical behavior of percolating ABS/CB nanocomposites. The experiments were aimed at controlling the processing parameters such as temperature, pressure and time during hot pressing of the mechanically mixed precursor materials. Using data obtained at the various temperature-pressure combinations used, it is shown that similar volume percentages of carbon black and carbon nanotubes can be used to obtain equivalent conductivities while still maintaining comparable mechanical properties. INTRODUCTION Acrylonitrile butadiene styrene (ABS) is a common engineering polymer that is used in a wide variety of applications. It is used in making pipes, golf club heads, LEGO™ bricks, and automotive parts, among other uses [1]. ABS is known for its strength, impact resistance, toughness and heat resistance. However, like most polymers, ABS is extremely insulating. With the addition of conductive fillers, electrical properties of ABS can be enhanced and allow for its use in other applications. Because of its heat and shock resistance, conductive ABS composites can be used for packaging of electronic devices [2,3]. Electrical shielding applications are also possible with conductive ABS polymer composites [4-6]. Carbon black is often used as the conductive filler to achieve conducting polymer composites. For an extensive review of carbon black used as a conductive filler in polymers, see Balberg [7].
In the literature, it has been shown that using a large polymer/filler size ratio can decrease the percolation threshold of a material substantitally[8-10]. The filler is often localized around the grain boundaries of the polymer, rather than spread throughout the full volume of the polymer[10]. We recently reported on the elec
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