Tough, self-healing and recyclable polyurea elastomer with dual dynamic crosslinked networks for sustainable flexible strain sensors.
Elastomers integrating self-healing capability, recyclability, and excellent mechanical performance have attracted considerable interest owing to their great application prospects in the emerging fields of soft robots, wearable electronics, and biomedical engineering. Herein, we synthesized a tough, self-healing and recyclable polyurea elastomer through the addition reaction of isophorone diisocyanate with polyether amine and 3,5-diaminobenzoic acid, followed by the incorporation of metal ions to construct dual dynamic crosslinked networks composed of multiple hydrogen bonds and metal-carboxylate coordination bonds. Unlike the Fe3+-coordinated polyurea elastomer, the Zn2+-coordinated polyurea elastomer achieved excellent mechanical performance, with a tensile strength of 10.89 MPa, an elongation at break of 1656% and toughness of 137.40 MJ m-3, which was attributed to the moderate coordination capability and homogeneous dispersion of Zn2+ ions, as confirmed by theoretical simulations and polarized light imaging. Benefiting from the formation of the dual dynamic crosslinked networks, the elastomer demonstrated superior self-healing capability with a healing efficiency of 93.5% at 60 °C for 24 h and remarkable recyclability through hot-press and solvent recycling methods with tensile strength retentions of 80.0% and 99.3% after three recycling cycles, respectively. In addition, a polyurea-elastomer-based tubular flexible strain sensor with liquid metal as a conductive substance for object recognition was highly sensitive, completely recyclable, and capable of self-healing. The findings in this work conceivably represent a new methodology for the preparation of high-performance, functional and sustainable elastomers and flexible sensors.