Polymer Testing 20 (2001) 33–41 www.elsevier.nl/locate/polytest Material Properties The effects of partial replacement of oil palm wood flour by silica and silane coupling agent on properties of natural rubber compounds Hanafi Ismail * , H.P.S. Abdul Khalil School of Industrial Technology, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia Received 1 September 1999; accepted 22 November 1999 Abstract The effects of partial replacement of oil palm wood flour (OPWF) by silica and silane coupling agent on mechanical properties and curing characteristics of natural rubber compounds were investigated. Compared to the control compound (50 phr of OPWF and without coupling agent), increasing the silica in the weight ratio of OPWF/silica and adding silane coupling agent increases the scorch time, t 2 and cure time, t 90 and enhances the tensile strength, tensile modulus, tear strength, fatigue life and hardness. Results from maximum torque–minimum torque indicate that the rubber-filler interaction is improved with the partial replacement of OPWF by silica and the presence of silane coupling agent.  2000 Elsevier Science Ltd. All rights reserved. Keywords: Oil palm wood flour; Silica; Silane coupling agent; Mechanical properties; Natural rubber 1. Introduction Short fibres are used in rubber compounding due to the considerable processing advantages, improvement in certain mechanical properties, and for economic con- siderations [1]. The addition of short fibre improves or modifies the properties of the composite. One of the most important criteria of composite manufacture is to achieve adequate adhesion between fibres and rubber matrix. Most attempts to solve this requirement involved grafting onto the fibres, the introduction of coupling agents to the rubber mix or pretreatment of the fibres with suitable agents [2]. Silane coupling agents have been used in the rubber industry for the last three decades to improve the performance of silica and other mineral fillers in rubber compounds. A silane coupling agent contains functional groups that can react with the rubber and the silica. In * Corresponding author. Tel.: + 60-04-6577888-2214; fax: + 60-04-657-3678. E-mail address: ihanafi@usm.my (H. Ismail). 0142-9418/00/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII:S0142-9418(99)00075-6 this way, the rubber-silica adhesion is increased and consequently the reinforcing effect of silica is enhanced [3]. In our previous work [4], the effects of oil palm wood flour (OPWF) loading and vulcanization system on properties of OPWF-natural rubber composites were studied. The incorporation of OPWF in natural rubber compounds increases the tensile modulus and hardness but decreases tensile strength, tear strength and elong- ation at break. However semi efficient vulcanization (semi-EV) composites exhibit better properties than con- ventional vulcanization composites. In this paper the effects of partial replacement of OPWF by silica and sil- ane coupling agent on properties of natural rubber com- pounds is reported. 2. Experimental 2.1. Materials and chemicals The formulations of the composites are given in Table 1. Composites were prepared using a conventional vul-