Alternative secondary accelerator for silica-filled natural rubber formulations

Abstract

Dithiophosphate (DTP) displays a good efficiency towards improved overall properties of silica-reinforced natural rubber compounds, when it is used as secondary accelerator in a sulfenamide primary accelerated sulfur vulcanization system. Comparing DTP with diphenylguanidine (DPG), DTP is more reactive and gives lower reversion leading to a lower amount required for vulcanization and better aging properties. An increase of chemically bound rubber content accompanied with a lowered Payne effect is obtained when secondary accelerator is used. A potential coupling ability of DTP can be postulated. The optimal amounts of DTP and DPG are approximately 0.8 and 1.1 phr, i.e. 1.4 and 2.0 wt% relative to silica content, respectively.