Influence of Sulfur Ratio to Accelerator on the Crosslink Density, Mechanical, Dynamic, and Damping Properties of Unfilled Natural Rubber Vulcanizate

Abstract

Natural rubber (NR) is a biopolymer with low vibration damping capacity. NR requires modification of its viscoelastic properties through crosslink in NR vulcanizates molecular chains as vibration damping. This study is the first to report a correlation between crosslink density and dynamic shear properties of NR vulcanizates, including hysteresis loop area, shear stiffness, equivalent damping ratio, and effective shear modulus. This correlation is necessary to develop NR vulcanizates properties appropriate to the vibration isolator product requirement. This research also reveals the rubber compound formulation technique to achieve the optimum value of the viscoelasticity and damping properties of NR vulcanizates by setting the crosslink density. In addition, this research investigates the influence of sulfur ratio to MBTS accelerator on the crosslink density, mechanical, dynamic, and vibration damping properties of unfilled NR vulcanizates. The crosslink density of unfilled NR vulcanizates is determined by the Mooney-Rivlin method. At the same time, the dynamic properties and vibration damping were evaluated by testing the dynamic shear properties. Testing results showed that the increment of sulfur to MBTS accelerator ratio increased crosslink density value. The highest crosslink density was measured at a 7.16 x 10-5 mol/cm3 obtained by NR vulcanizates containing sulfur to MBTS accelerator ratio at 2.15. This ratio also produced optimum value for mechanical properties (tear and tensile strength), elastic properties (compression set, LUPKE rebound resilience, and elastic modulus), and the highest effective shear modulus value. The value of tear strength, tensile strength, compression set, LUPKE rebound resilience, elastic modulus, and an effective shear modulus were 28.5 N/mm; 25.2 MPa; 3.65%; 79; 3.89 MPa, and 0.169 MPa. The optimum value of vibration damping was obtained at 1.39% of an equivalent damping ratio produced by NR vulcanizates containing sulfur to MBTS accelerator ratio at 0.14.