Mechanistic Investigation of Lecithin Enabled Efficient Vulcanization of Rubber With Reduced Zinc Oxide

Abstract

ABSTRACT In the conventional vulcanization of rubber, heavy reliance on zinc oxide (ZnO) results in resource waste and significant environmental pollution. Consequently, developing green and efficient strategies to reduce ZnO usage remains critical. In this study, lecithin, a bio‐based activator, is introduced into rubber to reduce ZnO usage during vulcanization. The addition of only 1.2 phr lecithin enables a 60% reduction in ZnO content while still maintaining the vulcanization efficiency and mechanical strength of natural rubber (NR). Notably, under reduced ZnO content, the NR sample with lecithin shows tensile strength increasing from 2.14 to 11.75 MPa compared to the sample without lecithin. Mechanistic investigations reveal that lecithin coordinates with Zn 2+ , which greatly improves dispersion of ZnO in the NR and enhances its utilization efficiency. Moreover, density functional theory (DFT) calculations confirm that lecithin‐Zn 2+ chelates increase the nucleophilicity of sulfur atoms in the accelerator toward elemental sulfur (S 8 ), lowering the Gibbs free energy for zinc polysulfide formation (Δ G is reduced from 71.59 to 55.68 kJ/mol) and accelerating vulcanization. In summary, lecithin acts as an effective bio‐based activator to enable a significant reduction in ZnO content without compromising the properties of NR. This approach provides a sustainable, efficient, and practical strategy for the development of low‐ZnO rubber composites.