Zn/Al‐ NO 3 Layered Double Hydroxide as Alternative Activator for Nitrile Rubber Vulcanization: Effect of the Accelerator‐to‐Sulfur Ratio on Curing Kinetics and Network Properties

Abstract

ABSTRACT Reducing zinc content in rubber formulations remains an important challenge due to environmental concerns associated with the use of zinc oxide (ZnO) as part of vulcanization systems. Zinc‐containing layered double hydroxides (Zn/Al‐LDHs) offer an alternative approach to incorporating zinc into lamellar structure and have been investigated as both vulcanization activators and fillers. However, the curing behavior of unmodified Zn/Al‐NO 3 LDH in conventional nitrile rubber (NBR) remains insufficiently understood. In this study, Zn/Al‐NO 3 LDH was evaluated as an alternative low‐zinc vulcanization activator for nitrile rubber (NBR) as a replacement for the ZnO/stearic acid system. Conventional (A/S = 0.6) and efficient (A/S = 3.0) sulfur‐curing systems were compared. In the conventional system, the LDH decreased the apparent Ea from 90.81 to 70.95 kJ.mol −1 and reduced the pre‐exponential factor by approximately two orders of magnitude. Tensile strength remained comparable, whereas tear strength decreased by approximately 14%. Thermogravimetric analysis showed a slight increase in the onset degradation temperature for the LDH‐containing formulations. Based on nominal compositions, replacing the ZnO/stearic acid activation system with Zn/Al‐NO 3 LDH corresponded to an estimated 71% reduction in zinc loading. Environmental benefits cannot be inferred from this reduction because zinc release, bioavailability, and ecotoxicological effects were not evaluated.