Phosphonium Ionic Liquid‐Activated Sulfur Vulcanization: A Way Forward to Reduce Zinc Oxide Levels in Industrial Rubber Formulations

Abstract

Extensive use of zinc oxide and accelerators such as diphenyl guanidine (DPG) in the vulcanization of rubber composites entail potential environmental risks. These are pervasive contaminants of roadway runoff originating from tire wear particles (TWPs). Herein, the effect of phosphonium ionic liquids (PILs) in styrene-butadiene rubber compounds was demonstrated with reduced ZnO loading and no DPG to minimize the environmental footprint of the vulcanization process. The structure and chemistry of PILs were found to be the influencing parameters impelling the cross-linking kinetics, enabling shorter induction times. The generation of active Zn 2 + sites by PILs was examined through FTIR spectroscopy, calorimetry, and molecular dynamics simulations. From a tire application perspective, the PILs not only enhanced the cure kinetics but also improved the dynamic-mechanical behavior of the rubber composites. Consequently, the harm caused by TWPs to the atmosphere, fuel intake, and CO 2 emissions was minimal, thereby confirming the potential use of PILs in the tire industry.

Curcuma Longa-Based Green and Sustainable Antioxidants for Biopolymers

“…In cross-linking chemistry (vulcanization process), the active bidentate zinc/stearate complex formation is the rate-determining step . For example, the S–N bond of the sulfenamide accelerator (CBS) dissociates at ∼140 °C, liberating free amine and 2-mercaptobenzothiazole and forming a bidentate zinc/stearate complex, as shown in Scheme .…”

“…The heat flow curve for the model cure recipe obtained from DSC measurements is depicted in Figure . The endothermic peaks 1–3 are related to the melting of stearic acid, CBS, and sulfur, followed by its phase transition, whereas the distinct exothermic peak (peak 4) corresponds to the bidentate Zn 2+ complex …”

Molecular Insights into Antioxidant Efficiency of Melanin: A Sustainable Antioxidant for Natural Rubber Formulations

“…Although numerous qualitative aging experiments exist on the antioxidation mechanism of antioxidant molecules, quantitative studies involving molecular insights into the antioxidant efficiency of natural antioxidant molecules are still inadequate. Computational tools predict materials’ dynamic and quantum mechanical (QM) properties on multiple scales. − Molecular theories have made the utmost advancement in the field of polymer nanocomposites for calculating equilibrium phase and macroscopic properties. − Thus, QM and MD simulations were meant to be carried out to investigate the relationship between the molecular structure and the chemical nature of the antioxidant molecules. The present study thus aims to examine the influence of the interfacial interactions among the antioxidants, polymer, and fillers on the interfacial bonding and the interphase antioxidant properties of the model nanocomposites, which are difficult to access experimentally.…”