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 Zn2+ salt bondings connect separate XSBR molecules. The further self-aggregation of ion pairs of Zn2+ 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 Zn2+ 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.