Multifunctional Elastomer Nanocomposites based on EPDM and Carbon Nanotubes
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Multifunctional Elastomer Nanocomposites based on EPDM and Carbon Nanotubes Paola Ciselli1,2, Lan Lu1,3, James J.C. Busfield1 and Ton Peijs1,2 1
School of Engineering and Materials Science, Centre for Materials Research, Queen Mary University of London, Mile End Road, E1 4NS, London, UK, E-mail: [email protected] 2 Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands 3 School of Chemistry and Chemical Technology, Shanghai Jiao Tong University, 200240 Shanghai, PR China ABSTRACT Elastomeric composites based on Ethylene-Propylene-Diene-Monomer (EPDM) filled with multi-wall carbon nanotubes (MWNTs) have been prepared, showing improved mechanical properties as compared to the pure EPDM matrix. The results have been discussed using the Guth model. The main focus of the study was on the electrical behavior of the nanocomposites, in view of possible sensor applications. A linear relation has been found between conductivity and deformations up to 10% strain, which means that such materials could be used for applications such as strain or pressure sensors. Cyclic experiments were conducted to establish whether the linear relation was reversible, which is an important requirement for sensor materials. INTRODUCTION This work is focused on piezoresistive behavior where a mechanical stimulus induces a change in resistivity. This property is the basis of many commercial pressure sensors and strain gauges. A piezoresistive effect is predicted for heterogeneous solids composed of conducting particles dispersed in an insulating polymer matrix, e.g. conducting polymer composites, CPCs [1]. Such materials are characterized by an insulator-to-conductor transition when a certain concentration of conducting particles is reached. This transition has been interpreted within the framework of percolation theory [2]. The percolation effect is related to the material microstructure. In particular, the separation between the conducting particles plays a crucial role on the electrical behavior of the bulk material. For CPCs with a certain filler loading, any parameter that can alter the interparticle distance will affect the conductivity. Several groups investigated the change of conductivity of CPCs as a function of temperature [3,4], solvent vapors [5-9], pressure [10] or mechanical stretching [11-21]. Such materials have the potential to become a new generation of sensors if the dependence is reversible. In this paper, the effect of incorporating small amounts of MWNTs into an Ethylene-Propylene-Diene-Monomer (EPDM) elastomeric matrix will be explored. The mechanical and electrical behavior will be studied, with an emphasis on the effect of strain on the conductivity. EXPERIMENTAL Materials Ethylene-Propylene-Diene-Monomer (EPDM) rubbers belong to the family of the ethylenepropylene (EPM) rubbers. Copolymerisation of ethylene with propylene gives an EPM rubber, which needs to be cross-linked. For that a third monomer, a diene, is added in small amounts (38% of the total monomer weight). The diene
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