Fire performance of engineered bamboo composites coated by phosphorus-based transparent intumescent flame-retardant coatings

The excellent mechanical properties and cost-effectiveness of engineered bamboo composites make it a promising alternative to traditional construction materials, but its fire hazards limit its further application. Applying transparent intumescent flame-retardant coating (TIFC) is an effective method to improve its fire performance while maintaining its natural aesthetic appearance. However, limited attempt has been made yet. This study prepared a phosphorus-based TIFC and investigated its performance in protecting three representative engineered bamboo composites (laminated bamboo (LB), bamboo scrimber (BS), and mold-resistant bamboo scrimber (MBS)) by limiting oxygen index (LOI) test, UL-94 test and cone calorimeter test. TIFC increased LOI values by 21.4–48.1% and reduced anisotropic differences. Coated bamboos were difficult to ignite by burner flame and exhibited immediate self-extinguishment. Under radiative cone heating, TIFC forms a porous, intumescent char layer that suppresses flammable gas release, provides thermal insulation, and prevents sustained flames and re-ignition. The second heat release peak and total heat release were reduced by 23.8–47.9% and 23.1–43.7%, respectively. After the cone calorimeter test, TIFC-coated bamboos present fewer cracks and greater structural integrity. The combined action of enhanced char formation, reduced volatile release, and improved barrier performance by the TIFC synergistically enhances the flame retardancy of the engineered bamboo composites. This work is expected to provide experimental insights for the fire safety design of bamboo structures.