X(3872), X(4014), and their bottom partners at finite temperature

Waterborne polyurethane has drawn extensive attention due to its environmental friendliness and is widely used in many areas. However, it is still a great challenge to synthesize waterborne polyurethanes with flame retardancy and fast room temperature self-healing ability, along with excellent mechanical performance and emulsion stability due to the mutually contradictory nature of these properties. Herein, waterborne polyurethanes containing organic selenium (SWPU-x) from 0.67 to 3.28 wt % were synthesized, which could simultaneously realize flame retardancy and self-healing ability based on the ability to scavenge active free radicals at high temperature and the dynamic switch of diselenide. All these SWPU-x films self-extinguished within 1 s after the ignition in the vertical combustion tests. The limiting oxygen index of SWPU-4 was improved to 28.5% with excellent UL-94 level (V-0) and self-healing efficiency (91.25%, after being healed in the photoreactor for 30 min at room temperature), together with high mechanical properties (tensile strength was 18.5 MPa and elongation at break was 869.63%), and the total heat release (THR) for SWPU-4 (49.28 MJ/m2) could decrease to 23.80% of the THR for the original waterborne polyurethane WPU (64.67 MJ/m2). This work discovered a new flame-retardant element (organic selenium) and studied its flame-retardant behaviors and self-healing function simultaneously, which would extremely extend the application of waterborne polyurethanes.

Automated summary

Waterborne polyurethane containing organic selenium was successfully synthesized, which exhibited excellent flame retardancy, self-healing ability, mechanical performance, and emulsion stability. The polymer achieved flame retardancy by scavenging free radicals and utilized the dynamic switch of diselenide for self-healing. The polymer self-extinguished within 1 second and showed high UL-94 level (V-0), self-healing efficiency (91.25%), and mechanical properties (tensile strength of 18.5 MPa and elongation at break of 869.63%). The total heat release was reduced by 23.80% compared to the original waterborne polyurethane.