Optimisation of oil palm ash as reinforcement in natural rubber vulcanisation: A comparison between silica and carbon black fillers

Oil palm ash (OPA) as filler was compounded with natural rubber (NR) using conventional laboratory-sized two roll mills. For comparison purposes, two commercial fillers (i.e. silica and carbon black) were also studied. The optimum loading of each type of filler was investigated and compared in terms of, curing characteristics, tensile properties, rubber-filler interaction and dynamic mechanical analysis. Results showed that scorch time and cure time of carbon black filled vulcanizates was the lowest compared to OPA and silica-filled NR vulcanizates. However, the incorporation of OPA offers the highest cure rate index. From a reinforcement perspective, the carbon black-filled vulcanizates had the highest tensile strength (26 MPa), followed by OPA (25 MPa) and silica (23 MPa). It is worth noting that the incorporation of OPA increased the elongation at break by 7.4% whereas silica and carbon black reduced the elongation at break of the NR compound. Further evidence of interaction was supported by the measurement of rubber-filler interaction, dynamic mechanical analysis and morphological studies.