Improving the thermal stability of polysulfidic crosslinks by hexamethylene‐1, 6‐bis(thiosulfate) disodium salt as the curing agent of natural rubber

Abstract

AbstractWhen vulcanized with sulfur, the natural rubber (NR) usually accompanies reversion, and the proportion of polysulfidic crosslinks decreases considerably, leading to significantly performance decay. In the rubber industry, hexamethylene‐1, 6‐bis(thiosulfate) disodium salt (HTS) is used as a multifunctional agent to improve not only the reversion and fatigue properties of NR, but also the adhesive properties between NR and steel cords. However, there is few research about the working mechanism of HTS. In this work, HTS is added to belt compounds in doses of 0 to 5 phr. The cure characteristics, crosslinking structures, physical‐mechanical properties, dynamic viscoelastic behavior, and T‐pull adhesion forces of the NR composites are investigated. The results show that the total crosslinking density and T‐pull adhesion forces of the composites both pass through a maximum and then decrease with the increasing dosage of HTS. Meanwhile, the formation of hybrid crosslinks during the prolonged cure time enhances the thermal stability and retention of the polysulfidic crosslinks of the NR composites. Surprisingly, the reduction in the proportion of polysulfidic crosslinks from optimum cure time (Tc90) to 60 min just reaches 15.9% with the addition of 5 phr HTS, whereas that value is 30.9% without adding HTS, which shows the excellent antireversion ability of the HTS in the belt compound. Our work reveals some new features of HTS, which can lead to a more profound understanding of HTS.