Synergistic Enhancement of the Flame Retardancy, Mechanical Properties, and Thermal Insulation of Rigid Polyurethane Foam via a Boron-Containing Chitosan Derivative

To overcome the performance barriers of rigid polyurethane foam (RPUF), a boron-containing chitosan derivative, CBPM, was synthesized. Boron phosphate (BP, acid source) and melamine (nitrogen source) synergistically promote the conversion of chitosan to carbon. The combustion tests demonstrate that the RPUF/20CBPM composite exhibits excellent flame retardancy, with a limiting oxygen index of 27.5% and a UL-94 flammability rating of V-0. Compared to pure RPUF, the heat release rate, total heat release, combustible gases, and hazardous gas release of RPUF/20CBPM are significantly reduced, while the residual carbon yield increases dramatically from 0.5% to 12.2% at 800 °C, indicating CBPM’s excellent smoke-suppression and char-forming capabilities. Furthermore, RPUF/20CBPM exhibits satisfactory mechanical properties and thermal insulation, with a compressive strength of 0.23 MPa and a thermal conductivity of 0.0347 W/(m·K). Actually, the CBPM significantly improves the flame retardancy of RPUF and synergistically enhances its mechanical properties and thermal insulation. This advancement provides a promising approach to develop safer, more durable, and higher-performance RPUF materials, potentially expanding their applications in building insulation, aerospace, and transportation materials.