Thermoreversible Nitrile Rubber Based on the Dual Role of Zinc Chloride

Abstract

A strategy for the preparation of thermoreversible nitrile rubber is demonstrated by introducing zinc chloride into sulfur-cured nitrile rubber to form metal coordination bonds, thereby constructing a dynamic double-crosslinking network as a potential solution for the severe environmental burden. In this study, the crosslinking structure and the mechanism of reprocessing are investigated by X-ray diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy, revealing that the crosslinking network is formed by monosulfide bonds, disulfide bonds, polysulfide bonds, and Zn²⁺-cyanide coordination bonds generated from zinc chloride that interact with the cyano groups on the nitrile rubber. Zinc chloride plays a dual role during the reprocessing process. On one hand, it participates in the cleavage/recombination of Zn²⁺-cyanide coordination bonds. On the other hand, it catalyzes the disulfide exchange reaction in the sulfur crosslinking system, enabling the recycled nitrile rubber to possess recyclability. Due to the double-crosslinking structure accompanied by the dual role of zinc chloride, nitrile rubber exhibits superior mechanical properties and impressive recyclability. The tensile strength and elongation at break of the double-crosslinking nitrile rubber reach 5.59 MPa and 387%, respectively, stronger than those of sulfur-cured nitrile rubber, maintaining 116.5% and 115.0% after the recycling process.