Comparative Study on Natural Antioxidant as an Aging Retardant for Natural Rubber Vulcanizates M. Komethi, 1 N. Othman, 1 H. Ismail, 1 S. Sasidharan 2 1 School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia 2 Institute For Research in Molecular Medicine (INFORMM), Universiti Sains Malaysia, 11800 USM, Penang, Malaysia Received 5 October 2010; accepted 26 June 2011 DOI 10.1002/app.35160 Published online 18 October 2011 in Wiley Online Library (wileyonlinelibrary.com). ABSTRACT: The research aim is mainly to investigate the effectiveness of natural antioxidant (NA) obtained from oil palm leaves (Elaeis guineensis) as an aging retard- ant in natural rubber (NR) vulcanizates. Comparison of NA with other commercial antioxidants, trimethyl quino- line (TMQ) and butylated hydroxy toluene (BHT), is inves- tigated. The effect of natural and commercial antioxidants on NR vulcanizates was explored before and after aging. Aging test was carried out at 70  C for three different peri- ods, 4, 7, and 14 days to determine aging property by per- forming the tensile and tear tests. NA shows lower tensile properties, crosslink density, tack strength but high tear strength compared to the commercial antioxidants, BHT and TMQ. However, upon aging NR vulcanizates with NA retains its properties equivalent to that of commercial antioxidants, BHT and TMQ. Thus, NA can be used as an aging retardant for short-term protection in application requiring moderate tensile properties and can be used as alternative source for commercial antioxidant. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 124: 1490–1500, 2012 Key words: natural antioxidant; Elaeis guineensis; aging retardant; natural rubber (NR); commercial antioxidants INTRODUCTION All around the globe, the quantity of waste materials is accumulating day by day. Thus, the use of waste materials has spurred the interests of many research- ers to explore the possibility to use alternative sour- ces. In rubber industry, the utilization of waste ma- terial in rubber compound becoming commercial and environmental interests. Rubbers are used for various indoor and outdoor applications. Concerning about the outdoor applica- tion, the rubber goods should be protected from ox- ygen, ozone, light, and heat to extend the service life or prevent aging of the vulcanized rubber goods. Most natural and synthetic rubbers containing unsat- urated backbones can be easily oxidized. For instance, natural rubber (NR) must be protected against oxygen. 1 The principal mechanism of oxygen attack involves an autocatalytic, free radical reaction. The first step is the formation of macroradicals as a result of hydrogen abstraction from rubber chains by proton acceptor. Oxidation continues by reaction of macroradicals with oxygen and the subsequent for- mation of peroxy radicals and hydrperoxides. 2 The mechanism of rubber degradation by oxidation under thermal energy is depicted as in Scheme 1. 1 The oxidative degradation results in aging which leads to the deterioration in the physical and me- chanical properties of vulcanized rubbers. This becomes one of the major problems in rubber technology. 3 To counteract the deterioration of the rubber, whether by natural or accelerated aging, these types of deterioration can be retarded but not completely avoided by the addition of antioxidants. 4 Antioxi- dants react with oxygen to prevent oxidation of vul- canized rubber and react with free radicals that de- grade vulcanized rubber. A schematic chain termination or the stabilization of rubber chains by antioxidant is presented in Scheme 2. 1 The most common antioxidants for rubber are derivatives of aromatic amines and phenols. Amines are more effective in preventing long-term oxidative degrada- tion for most of rubber systems. However, amine antioxidants usually discolor with aging and may not be correct choice for light and brightly colored rubber goods where color retention is important. In contrast to amine antioxidants, phenolic antioxidants do not discolor on aging but are generally less effec- tive in preventing long-term oxidative degradation. 4 Many commercial antioxidants such as trimethyl- quinoline (TMQ) and butylated hydroxy toluene Correspondence to: N. Othman (srnadras@eng.usm.my). Contract grant sponsor: Yayasan Felda; contract grant number: 6050146. Journal of Applied Polymer Science, Vol. 124, 1490–1500 (2012) V C 2011 Wiley Periodicals, Inc.