Material properties Comparative study on the effect of partial replacement of silica or calcium carbonate by bentonite on the properties of EPDM composites H. Ismail * , M. Mathialagan Division of Polymer Engineering, School of Materials & Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia article info Article history: Received 12 July 2011 Accepted 5 September 2011 Keywords: Bentonite EPDM Tensile properties Dynamic mechanical analysis Composite abstract The effects of the partial replacement of silica or calcium carbonate (CaCO 3 ) by bentonite (Bt) on the curing behaviour, tensile and dynamic mechanical properties and morpho- logical characteristics of ethylene propylene diene monomer (EPDM) composites were studied. EPDM/silica/Bt and EPDM/CaCO 3 /Bt composites containing five different EPDM/ filler/Bt loadings (i.e., 100/30/0, 100/25/5, 100/15/15, 100/5/25 and 100/0/30 parts per hundred rubber (phr)) were prepared using a laboratory scale two-roll mill. Results show that the optimum cure (t 90 ) and scorch (t S2 ) time decreased, while the cure rate index (CRI) increased for both composites with increasing Bt loading. The tensile properties of EPDM/ CaCO 3 /Bt composites increased with the replacement of CaCO 3 by Bt from 0 to 30 phr of Bt. For EPDM/silica/Bt composites, the maximum tensile strength and E b were obtained at a Bt loading of 15 phr, with enhanced tensile modulus on further increase of Bt loading. The dynamic mechanical studies revealed a strong rubber-filler interaction with increasing Bt loading in both composites, which is manifested by the lowering of tan d at the glass transition temperature (Tg) for EPDM/CaCO 3 /Bt composites and tan d at 40  C for EPDM/ silica/Bt composites. Scanning electron microscopy (SEM) micrographs proved that incorporation of 15 phr Bt improves the dispersion of silica and enhances the interaction between silica and the EPDM matrix. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The reinforcement of rubber is primarily related to the enhancement of strength, stiffness and modulus, hardness and abrasion resistance. Previously, a variety of particulate fillers have been used in the rubber industries mainly for reinforcement purposes, for the reduction of material costs and to improve processability [1]. Carbon black (CB) has exploited in numerous rubber products to increase the tensile strength, tear strength, modulus and abrasion resistance. However, CB is synthesised from petroleum feedstock, which causes pollution issues and gives a dark colour to the rubber products [2]. Several studies have been performed in past decades on replacing CB with various types of light-coloured, mineral and natural fillers such as silica [3,4], calcium carbonate [5,6] and clay [7,8]. Silica is commonly used as a reinforcing filler in rubber compounding, and it provides a unique combination of tear strength, abrasion and aging resistance and adhesion properties [9]. However, the properties are lower than those of CB due to the inorganic nature of silica, which results in poor dispersion and incompatibility with hydrophobic elastomeric materials [4,10]. Calcium carbonate (CaCO 3 ) is another type of light-coloured mineral filler used as a non-reinforcing filler in rubber products to reduce material costs and improve the bulk properties. However, aggregation and the larger particle size of CaCO 3 results in processing problems, deteriorated mechanical properties and poor aesthetics [5]. * Corresponding author. Tel.: þ60 4 599 6113; fax: þ60 4 594 1011. E-mail address: hanafi@eng.usm.my (H. Ismail). Contents lists available at SciVerse ScienceDirect Polymer Testing journal homepage: www.elsevier.com/locate/polytest 0142-9418/$ – see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymertesting.2011.09.002 Polymer Testing 31 (2012) 199–208