Article An alternative antioxidant for sulfur-vulcanized natural rubber: Henna S ¸ ehriban O ¨ ncel 1,2 , Begu ¨ m Kurtog ˘lu 1 and Bag ˘ dagu ¨ l Karaag ˘ac ¸ 1,3 Abstract Oxidative aging of natural rubber (NR) leads to the deterioration in the physical and mechanical properties. Using various antioxidants during compounding is a common way to improve the aging resistance of NR. The most widespread used antioxidants are phenolic and amine-based synthetic antioxidants and 2,2,4-trimethyl-1,2- dihydroquinoline in rubber industry. However, synthetic antioxidants cause some environmental problems during their production and tend to be replaced by natural alternatives. In this study, henna has been evaluated as a natural antioxidant in NR-based rubber compounds for efficient and conventional sulfur vulcanization systems. Perfor- mance of henna was evaluated in terms of rheological, mechanical, aging, and tem- perature scanning stress-relaxation properties of the compounds. It has been concluded that henna could be used as an alternative antioxidant for sulfur vulcanization of natural rubber matrix, compensating little deteriorations in vulcanizate properties. Short- and long-term performances of henna were also found to be related to vulcanization system. Keywords Natural rubber, aging, mechanical properties, antioxidant, thermal properties Introductıon Natural rubber (NR) is the most widely used raw material for many industrial applica- tions requiring satisfactory mechanical strength, adhesion ability, and resilience. 1,2 It is mainly consumed in tire and anti-vibration material production as 42% of total. 3 1 Department of Polymer Science and Technology, Kocaeli University, Kocaeli, Turkey 2 Ford Otosan Ihsaniye Vocational School of Automotive, Kocaeli University, Kocaeli, Turkey 3 Department of Chemical Engineering, Kocaeli University, Kocaeli, Turkey Corresponding author: Bag ˘dagu ¨l Karaag ˘ac ¸, Department of Chemical Engineering, Engineering Faculty, Kocaeli University, Umuttepe Campus, 41380 Kocaeli, Turkey. Emails: bkaraagac@kocaeli.edu.tr; bagdagul.karaagac@gmail.com Journal of Elastomers & Plastics 1–17 ª The Author(s) 2018 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/0095244318796594 journals.sagepub.com/home/jep