Flame-Retardant\nand Self-Healing Waterborne Polyurethane\nBased on Organic Selenium

Abstract

Waterborne\npolyurethane has drawn extensive attention due to its\nenvironmental friendliness and is widely used in many areas. However,\nit is still a great challenge to synthesize waterborne polyurethanes\nwith flame retardancy and fast room-temperature self-healing ability,\nalong with excellent mechanical performance and emulsion stability\ndue to the mutually contradictory nature of these properties. Herein,\nwaterborne polyurethanes containing organic selenium (SWPU-<i>x</i>) from 0.67 to 3.28 wt % were synthesized, which could\nsimultaneously realize flame retardancy and self-healing ability based\non the ability to scavenge active free radicals at high temperature\nand the dynamic switch of diselenide. All these SWPU-<i>x</i> films self-extinguished within 1 s after the ignition in the vertical\ncombustion tests. The limiting oxygen index of SWPU-4 was improved\nto 28.5% with excellent UL-94 level (V-0) and self-healing efficiency\n(91.25%, after being healed in the photoreactor for 30 min at room\ntemperature), together with high mechanical properties (tensile strength\nwas 18.5 MPa and elongation at break was 869.63%), and the total heat\nrelease (THR) for SWPU-4 (49.28 MJ/m²) could decrease to\n23.80% of the THR for the original waterborne polyurethane WPU (64.67\nMJ/m²). This work discovered a new flame-retardant element\n(organic selenium) and studied its flame-retardant behaviors and self-healing\nfunction simultaneously, which would extremely extend the application\nof waterborne polyurethanes.