Al<sub>2</sub>O<sub>3</sub> Decorated with Zn Single\nSites: A Multifunctional Filler for Upgrading the Properties of XNBR\nComposites

A multifunctional alumina-based filler, Al<sub>2</sub>O<sub>3</sub>@APTES-Zn, has been synthesized by functionalizing Al<sub>2</sub>O<sub>3</sub> nanoparticles with aminopropyl triethoxysilane\n(APTES)\nand subsequently anchoring Zn<sup>2+</sup> centers. This multifunctional\nnanofiller acts simultaneously as a reinforcing agent, cross-linking\npromoter, and thermal conductivity enhancer in carboxylated nitrile\nrubber (XNBR) composites. The anchored Zn(II) sites also provide ionic\ninteractions with XNBR terminations, enabling dynamic reversible bonds\nfor self-healing properties. The comprehensive characterization of\nXNBR/Al<sub>2</sub>O<sub>3</sub>@APTES-Zn composites unveils enhanced\ncross-linking, improved tensile strength and strain at break (up to\n17 MPa and 1416% at 24 phr filler), increased thermal conductivity\n(+11.4% compared to neat Al<sub>2</sub>O<sub>3</sub> at the same loading),\nand superior self-repairing efficiency (up to 120%). These results\ndemonstrate that the tailored surface and interfacial properties of\nAl<sub>2</sub>O<sub>3</sub>@APTES-Zn represent a promising benchmark\nfor resilient and sustainable composites in applications, such as\nhoses, seals, gaskets, and automotive components.