Sepiolite Nanofibers Decorated With Zn Single Sites: A Sustainable Filler for Mechanically Robust and Self-Healing Ionomeric Elastomer Composites

The growing demand for sustainable elastomer management has prompted the development of self-healing cross-linked rubbers. Recent studies showed that adding ZnO to carboxylated nitrile rubber (XNBR) creates thermo-reversible ionic interactions. However, Zn leaching during life cycles of rubber products raises environmental concerns. Moreover, achieving both efficient repairability and high mechanical performances in elastomers remains a major challenge. To address these issues, this work introduces a novel multifunctional filler based on sepiolite nanofibers (Sep) surface decorated with Zn(II) single sites. This is designed to simultaneously provide structural reinforcement, thermally activated self-healing properties and ensure potential reduced metal leaching from XNBR composites. Specifically, naturally occurring Sep was surface functionalized with an amino-substituted silane (APTES) to promote the coordination of Zn(II) centers. Following surface and morphological characterization, Sep@APTES-Zn was incorporated into XNBR to enable the formation of a thermo-reversible ionic network mediated by Zn(II) cations and allow rubber recovery after damage. Indeed, XNBR/Sep@APTES-Zn composites display excellent mechanical properties, remarkable self-repairability and pronounced potential recyclability. Moreover, the structural stability of Zn(II) sites in the materials represents a valuable turning point toward the potential reduction of Zn leaching phenomena. These findings may open new avenues to design and fabricate high-performance and sustainable rubber products with extended service lifetime.