Design of “Zn²⁺ Salt-Bondings” Cross-Linked Carboxylated Styrene Butadiene Rubber with Reprocessing and Recycling Ability via Rearrangements of Ionic Cross-Linkings

Constructing a reversible supramolecular network cross-linked by noncovalent bonds is an effective approach to realize self-healing as well as reprocessing and recycling for rubbers. Unfortunately, in most case the resultant noncovalent cross-linked rubbers cannot hold enough forces to meet the routine applications. In this paper, our strategy was based on a simple reaction between carboxy groups in carboxylated styrene butadiene rubber (XSBR) and zinc oxide (ZnO), where the formed Zn 2+ salt bondings connect separate XSBR molecules. The further self-aggregation of ion pairs of Zn 2+ salts resulted in an ionic cross-linked network, whose rearrangements brought XSBR excellent reprocessing/recycling ability. Additionally, the reclaimed XSBR exhibited valuable mechanical properties due to the compensation of additional formed new Zn 2+ salt bondings during recycling. The fresh XSBR with 5 wt % zinc oxide showed a tensile strength of 6.7 MPa, and it was further increased to 10.3 MPa after 3 recycles, which was far higher than most reported noncovalent supramolecular rubbers. This study thus opens up an avenue to further extending the recyclable cross-linked XSBR with considerable mechanical properties to various engineering applications.