Room-Temperature\nSelf-Healable and Mechanically Robust\nThermoset Polymers for Healing Delamination and Recycling Carbon Fibers

Abstract

The advocacy of carbon\nneutrality and circular economy encourages\npeople to pursue self-healing and recycling of glassy thermoset polymers\nin a more realistic and energy-saving manner, the best being intrinsic\nhealing under room temperature. However, the high mechanical robustness\nand healing ability are mutually exclusive because of their completely\nopposite requirements for the mobility of the polymer networks. Here,\nwe report a dual-cross-linked network by slightly coupling the low-molecular-weight\nbranched polyethylenimine with an ester-containing epoxy monomer in\na nonstoichiometric proportion. The highly mobile and dense noncovalent\nhydrogen bonds at the chain branches and ends can not only complement\nthe mechanical robustness (tensile strength of 61.6 MPa, elastic modulus\nof 1.6 GPa, and toughness of 19.2 MJ/m³) but also endow\nthe glassy thermoset polymer (<i>T</i>_g >\n40\n°C) with intrinsic self-healing ability (healing efficiency >\n84%) at 20 °C. Moreover, the resultant covalent adaptive network\nmakes the thermoset polymer stable to high temperatures and solvents,\nyet it is readily dissolved in ethylene glycol through internal catalyzed\ntransesterification. The application to room temperature delamination\nhealing and carbon fiber recycling was demonstrated as a proof-of-concept.