African Journal of Pure and Applied Chemistry Vol. 4(9), pp. 198-205, October 2010 Available online at http://www.academicjournals.org/AJPAC ISSN 1996 - 0840 ©2010 Academic Journals Full Length Research Paper Natural rubber/organoclay nanocomposites: Effect of filler dosage on the physicomechanical properties of vulcanizates L. E. Yahaya 1 *, K.O. Adebowale 2 , A. R. R. Menon 3 , S. Rugmini 3 , B. I. Olu-Owolabi 2 and J. Chameswary 3 1 Cocoa Research Institute of Nigeria, Ibadan, Nigeria. 2 Department of Chemistry, University of Ibadan, Ibadan, Nigeria. 3 National Institute for Interdisciplinary Science and Technology, Trivandrum, India. Accepted 1 September, 2010 Natural rubber/organoclay nanocomposites of varying filler loading [2 to 10 per hundred rubber (phr)] using derivative of tea (Camellia sinensis) seed oil were prepared by melt intercalation. Effects of filler dosage on the physicomechanical properties of the natural rubber (NR) vulcanizates were examined. Results of the mechanical properties indicates that tensile strength and tear properties of the modified organoclay/NR nanocomposites increases with increasing filler loading compared with the unmodified filled NR vulcanizates. Furthermore, rheological measurement showed that modified filled NR vulcanizate exhibited higher storage modulus (G I ) than the unmodified filled NR. The values of the weight-swelling ratio (Qt) of the modified filled nanocomposites decreased remarkably and are lower than the unmodified filled NR vulcanizate. The higher value of the chemical crosslink density of 0.629 at 6 phr for the organoclay/NR composite indicate better reinforcement of the filler-rubber matrix over the unmodified. The scanning electron microscopy revealed that incorporation of modified organoclay up to 6 phr has transformed the failure mechanism of the resulting NR vulcanizate compared to the unmodified. There is an indication that the optimum level of incorporation of sodium salt of tea seed oil is 6 phr. Key words: Vulcanizate, physicomechanical, nanocomposite, Camellia sinensis, natural rubber, organoclay. INTRODUCTION The field of polymer-clay nanocomposites has experienced rapid growth in the past decades. This class of materials has assumed considerable importance and has been the focus of extensive investigation (Kojima et al., 1993; Gianelis, 1996; Biswas and Sinharay, 1998; Lagaly and Pinnavaia, 1999; Gianelis et al., 1999; Hasegawa et al., 2000; Pinnavaia and Beall, 2000; Pramanik et al., 2001; Kim et al., 2001; Mannias et al., 2001; Ray and Bhowmick, 2002). They are materials that consist of two or more materials with one having a dimension in the nanometer range that is, one billionth of a meter. They are material which is an embodiment of *Corresponding author. E-mail: eugeneyah@yahoo.co.uk. et al., 2004; Nagi et al., 2008). In polymer nanocomposites, a few weight percent of each silicate layer of clay mineral is randomly homogenously dispersed on a molecular level in the polymer matrix. Following molding, the mechanical, thermal and barrier properties of the resulting material is superior to the virgin polymer (Usuki et al., 2002; Sinham Ray et al., 2003; Utra, 2004; Zheng et al., 2004; Zanetti and Costa, 2004; Okada and Usuki, 2006). Clay has been used as filler for natural rubber over the years, however the reinforcing property is poor and this is largely due to the large particle size and low surface activity. In recent times, improving the reinforcing ability of clay is by altering the hydrophilic nature of clay to organophillic. This is achieved by ion exchange of the clay interlayer cations such as alkyl ammonium or