DOI: 10.22146/ajche.80712 ASEAN Journal of Chemical Engineering 2023, Vol. 23, No. 3, 290 – 300 Physical Properties Investigation of Natural Rubber Composites Using Cetyltrimethylammonium Bromide (CTAB) as Modifier of Local Clay Filler Abu Hasan *, 1,2 Robert Junaidi 2 Muhammad Yerizam 1,2 Fatahul Arifin 1,3 1 Applied Magister of Renewable Energy, Politeknik Negeri Sriwijaya, jl. Srijaya Negara Bukit Besar Palembang 30139, Indonesia 2 Department of Chemical Engineering, Politeknik Negeri Sriwijaya, jl. Srijaya Negara Bukit Besar Palembang 30139, Indonesia 3 Department of Mechanical Engineering, Politeknik Negeri Sriwijaya, jl. Srijaya Negara Bukit Besar Palembang 30139, Indonesia * e-mail: abu_hasan@polsri.ac.id Abstract. Improved absorption of rubber backbone on filler surfaces is necessary to enhance the physical properties of rubber vulcanizate. One of the ways to repair the surface of the filler is through modifying using surfactant. Hence, this study aims to compare the physical properties of natural rubber vulcanizates using clay filler and modified clay with cetyltrimethylammonium bromide (CTAB). The processes that were followed to achieve the objectives of this research were the design of rubber formulas, mastication and milling of rubber, and testing of the physical properties of rubber vulcanization. The clay characterization and its modification using FTIR and XRD were also carried out. Characterization using FTIR and XRD showed that there was indeed a clay modification with CTAB. Natural rubber compounds were also analyzed using SEM. The torque on the rheometer for modified clay with CTAB is 12.34 kg-cm higher than for original clay, which is 7.05 kg-cm. Elongation at break and tensile strength for vulcanizate using CTAB-modified clay filler is lower than that using original clay, with 300% modulus and hardness increase. Thus, clay modification using CTAB as a filler has a good effect on the curing characteristics and physical properties of natural rubber vulcanization compared to only using local clay as a filler. Keywords: Crosslink density, Local clay, Modified clay, Natural rubber, Surfactant INTRODUCTION Fillers are supporting materials in manufacturing finished rubber products (Morton, 1987). A variety of fillers have been used. Fillers are divided into reinforcing, semi-reinforcing, and non-reinforcing fillers. These three fillers each have their characteristics when used as a filler. Reinforcing filler, which is well known and cannot be replaced until now, is carbon black. Carbon black produces CO2, so many researchers and practitioners have tried to reduce its use, for example, the use of a Submitted 28 December 2022 Revised 20 October 2023 Accepted 8 December 2023