Technical report Latex stage blending of multiwalled carbon nanotube in carboxylated acrylonitrile butadiene rubber: Mechanical and electrical properties K. Preetha Nair a , Paulbert Thomas b , Rani Joseph a,⇑ a Department of Polymer Science and Rubber Technology, Cochin University of Science and Technology, Kochi 682 022, India b Department of Electronics, Cochin University of Science and Technology, Kochi 682 022, India article info Article history: Received 6 March 2012 Accepted 10 April 2012 Available online 25 April 2012 abstract Multiwalled carbon nanotube (MWCNT) was dispersed in sodium dodecyl benzene sulphonate (SDBS) by sonication. The dispersed MWCNT (0.05–0.3 gm) was incorporated in carboxylated acrylonitrile butadi- ene rubber (XNBR) latex. Mechanical, electrical and thermal properties of these composites were studied. Mechanical properties of the composites increased up to an optimum concentration and then decreased. Dielectric properties of the composites were studied in the S band (frequency range 2–4 GHz) by Cavity Perturbation method. Direct current (DC) electrical conductivity shows a percolation behaviour and con- ductivity increased by about 10 orders of magnitude. Thermal studies were conducted using Differential Scanning Calorimetry (DSC) and Thermo Gravimetric Analysis (TGA). As expected with the very small concentration of multiwalled carbon nanotube, glass transition temperature (T g ) and thermal stability of the composite showed a marginal increase. Composites were characterized by Fourier transform infra- red spectroscopy (FTIR), X-ray diffraction (XRD) and Scanning electron microscope (SEM) analysis. Ó 2012 Published by Elsevier Ltd. 1. Introduction Synthesis of buckminster fullerene C 60 in 1985 stimulated the researchers worldwide to search for new forms of carbon other than graphite and diamond. Sumio Lijima discovered fullerene related carbon nanotube in 1991. Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical structure. They are considered as graph- ene sheets rolled into cylinders, 10,000 times thinner than a human hair [1]. These cylindrical nanotubes have exceptional properties which are useful in the field of nanotechnology, electronics, optics and other fields of material science. Production methods include classical approaches such as the arc discharge method, chemical vapour deposition method and laser ablation method [2] along with new methods like use of solar energy, electrolysis [3] plasma torch method. In CNT the carbon atoms are sp 2 bonded, with each carbon atom joined to three neighbours, as in graphite. The high polarizability of p-electron cloud leads to strong van der Waals attraction between carbon nanotubes [4]. The van der Waals attraction of carbon nanotubes leads to significant agglomeration. Agglomeration of CNT in polymer composites may cause a reduction in properties. So to get an effective reinforcement carbon nanotubes should not form aggregates and must be well dispersed. To enhance the inter- facial interaction with the matrix, it must be dispersed individually and homogeneously within the matrix [5]. Use of surfactants is an effective way for dispersing carbon nanotubes. The surfactant molecules orient themselves in such a fashion that hydrophobic tail groups face towards the nanotube surface and the hydrophilic head groups face towards the aqueous phase producing lowering of nanotube/water interfacial tension [6]. Reports show that the outermost nanotubes in a bundle are treated more than the innermost tubes and the nanotube remains predominantly bundled even after surfactant treatment [4]. But mechanical methods like ultrasonication can debundle the nano- tubes by steric or electrostatic repulsions [7]. On sonication the high local shear will unravel the outer carbon nanotubes in a bun- dle and expose other sites for additional surfactant adsorption, thus the surfactant molecules gradually exfoliate the bundle in an ‘‘unzippering’’ mechanism [8]. Some of the common surfactants used for the dispersion of car- bon nanotubes are sodium dodecyl benzenesulphonate (SDBS) [6], dodecyl trimethyl ammonium bromide (DTAB) [9], hexa decyl tri- methyl ammonium bromide (CTAB) [10], octyl phenol ethoxylate (Triton X-100) [11], and sodium dodecyl sulphate (SDS) [12]. Here SDBS is used as a surfactant to disperse CNTs. The high dispersing power of the SDBS is due to the presence of an aromatic unit which enhances the adsorption to the graphitic surface due to p–p stack- ing type interaction [8]. Tube stabilization depends on the surfac- tant molecules that lie on the tube surface parallel to the cylindrical axis [13]. Literature reports the preparation of MWCNT elastomer com- posites by different methods. Atieh et al. have prepared styrene butadiene rubber-multiwalled carbon nanotube (SBR-MWCNT) 0261-3069/$ - see front matter Ó 2012 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.matdes.2012.04.021 ⇑ Corresponding author. Tel.: +91 484 2575723 (O); fax: +91 484 2577747. E-mail address: rani@cusat.ac.in (R. Joseph). Materials and Design 41 (2012) 23–30 Contents lists available at SciVerse ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes