Hexamethylene diamine-modified epoxidized natural rubber and its effect on cure characteristics and properties of natura
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ORIGINAL RESEARCH
Hexamethylene diamine‑modified epoxidized natural rubber and its effect on cure characteristics and properties of natural rubber blends Rutchanon Longseng1 · Chuanpit Khaokong1 Received: 29 February 2020 / Accepted: 9 September 2020 © Iran Polymer and Petrochemical Institute 2020
Abstract Compatibility is a serious problem in silica-added natural rubber (NR) because of the difference in the polarities of silica and NR. Thus, a coupling agent, such as silane, or a compatibilizer must be incorporated. In this work, amine-functionalized NR was synthesized by an in situ epoxidation process using performic acid and later modified with hexamethylene diamine (HMDA) by a ring-opening reaction. The effects of amine-modified epoxidized NR (ENR-HMDA) content on the cure characteristics, physical and mechanical properties of various NR blends (NR/ENR-HMDA) without filler were studied. ENR-HMDA enhanced the vulcanization process. The maximum torque of compounds increased with the corporation of ENR-HMDA and scorch time and cure time decreased. The cure rate index of NR/ENR-HMDA increased by 98%. All vulcanized rubber blends showed the strain-induced crystallization at high extension. Mechanical properties and crosslink density of the blends were higher than those of NR and NR incorporated with unmodified ENR. Tensile strength was 61% and 43% higher than that for NR and NR/ENR, respectively. The NR/ENR-HMDA blends showed a single Tg that indicated the miscibility of both components. The developed ENR-HMDA compound can be used to improve the compatibility of NR and fillers which would enable the fabrication of a wide range of rubber products. Keywords Ring-opening reaction · Natural rubber modification · Rubber blend · Acceleration · Degree of curing · Rate of vulcanization
Introduction Natural rubber (NR) is a versatile bio-based, renewable resource with excellent properties. It is flexible, highly elastic and tough, with low heat build-up during its utilization. However, a certain amount of filler must be added to NR to improve tensile strength, tear resistance, modulus and hardness. It is well known that the dispersion of filler and the interfacial interactions between the rubber matrix and filler particles are factors that determine the properties of rubber composites, especially inorganic fillers. The fillers mainly used in rubber products are carbon black and silica. Carbon black is more compatible with rubber than silica, which is an inorganic filler, and hence, it is the most widely used filler but cannot be used in colored products for which silica * Chuanpit Khaokong [email protected] 1
Department of Materials Science and Technology, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand
is preferred. The patent of Michelin, cited by Sattayanurak et al. asserted that replacing carbon black with silica in tire tread compounds produced tires with lower rolling resistance and better wet grip [1]. However, the difference in the polarities of silica and NR poses a
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