Study of the Thermomechanical and Electrical Properties of Conducting Composites Containing Natural Rubber and Carbon Black Fernando A. Oliveira, 1 Neri Alves, 1 Jose ´ A. Giacometti, 1 Carlos J. L. Constantino, 1 Luiz H. C. Mattoso, 2 Ana M. O. A. Balan, 1 Aldo E. Job 1 1 Faculdade de Cie ˆncias e Tecnologia, UNESP, CP 467, 19060-900, Presidente Prudente, SP, Brazil 2 Embrapa Instrumentac ¸a ˜o Agropecua ´ria, CP 741, 13560-970, Sa ˜o Carlos, SP, Brazil Received 2 May 2006; accepted 23 December 2006 DOI 10.1002/app.26689 Published online 5 July 2007 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: This work describes the preparation and characterization of composite materials obtained by the combination of natural rubber (NR) and carbon black (CB) in different percentages, aiming to improve their mechanical properties, processability, and electrical conductivity, aim- ing future applications as transducer in pressure sensors. The composites NR/CB were characterized through optical microscopy (OM), DC conductivity, thermal analysis using differential scanning calorimetry (DSC), dynamic mechani- cal thermal analysis (DMA), thermogravimetry (TGA), and stress–strain test. The electrical conductivity varied between 10 29 and 10 S m 21 , depending on the percentage of CB in the composite. Furthermore, a linear (and reversible) de- pendence of the conductivity on the applied pressure between 0 and 1.6 MPa was observed for the sample with containing 80 wt % of NR and 20% of CB. Ó 2007 Wiley Peri- odicals, Inc. J Appl Polym Sci 106: 1001–1006, 2007 Key words: natural rubber; thermal properties; conducting polymers; composite film; piezoresistive sensor INTRODUCTION Electrically conducting polymers such as polyaniline have been subject of intense studies due to the great interest in their potential technological applications. However, the low electrical stability widely restricts their practical applications to a few cases. Alterna- tively, electrical conducting composites have been suc- cessfully prepared by adding conducting filler to poly- meric materials. For instance, conducting rubbery com- posites with carbon black (CB) are interesting due to their successful applications in electromagnetic shield- ing, electrostatic charge dissipation, 1 sensor of vehicle weight to collect tolls in the highways, 2 pressure sen- sor, 3,4 and selective gas sensor. 5 The electrical conduc- tivity of polymeric composites depends on the nature of the polymeric matrix and particles, such as its size, geometrical structure, surface, and their dispersion of the particles as well as the test conditions such as tem- perature and pressure. 6 Different physical processes are proposed to explain the mechanism of transport of electrons, and the dominant process is dependent on the composition of the mixture and on the conditions of the sample preparation. 7 Basically, three physical processes govern the transport of the electrons: perco- lation, tunneling, and thermal expansion. 8 Pressure sensors based on polymeric materials as thick or thin films are advantageous due to their low cost and easier fabrication process. They have been employed for medical, industrial, sports applications, and more recently as wearable sensors. 9–11 Piezoelectric polymeric and ceramic materials have been used as host for sensor applications 12 and piezoresistive materials are often used as transducer material in sensors. 13–15 In the latter, the variation of the electric conductivity with an applied pressure is the principle for its utilization as sen- sors and they have been produced from a large variety of materials such as the conductive polymers, electrical conductive composites, blends, and foams. 3,16,17 In this work, we have complemented our previous work on the electrical conductivity of composite films of natural rubber and carbon black 4 with thermome- chanical and electrical properties as the first step aim- ing to explore theses materials as transducers in pres- sure sensors. EXPERIMENTAL Composite preparation The latex of Hevea brasiliensis, clones RRIM-600 (RRIM-Rubber Research Institute of Malaysia), was collected from different trees from Presidente Pru- dente, Sa ˜o Paulo State, Brazil. The stabilization of Correspondence to: A.E. Job (job@fct.unesp.br). Contract grant sponsors: FAPESP; FUNDUNESP; CNPq; IMMP/MCT (Brazil). Journal of Applied Polymer Science, Vol. 106, 1001–1006 (2007) V V C 2007 Wiley Periodicals, Inc.