A novel flame-retardant polyurethane coating with self-healing function by photothermal conversion

Polyurethane (PU) materials are widely utilized in the design of self-healing material systems. Due to their poor flame resistance and violent droplet behavior during combustion, challenges remain in achieving PU materials exhibiting self-healing, flame retardancy, and robust mechanical performance. Here, a self-healing flame-retardant composite coating (PU-3) was developed by incorporating PDA@EG, a filler prepared by coating expanded graphite (EG) with polydopamine (PDA), into a PU matrix featuring multiple hydrogen bonds and disulfide bonds. As a photothermal conversion agent, PDA@EG enables PU-3 to achieve rapid photothermal conversion (82.9 °C within 3 min), a toughness repair efficiency of 93.79 % under near-infrared (NIR) light for 10 min, and repeatable self-healing. Additionally, PDA@EG can also act as a flame retardant, mitigating the dripping behavior and increasing the limiting oxygen index (LOI). The essence is as a charring agent to form a completely expanded carbon layer after heating, preventing the exchange of O₂ and heat. The synergistic interaction between PDA@EG and the hydrogen bond/disulfide bond matrix enables the combined self-healing and flame-retardant properties of PU-3. This work provides a heuristic perspective for the design of self-healing flame-retardant coating.