Flame-retardant composite derived from polyurethane/wood-fiber

Wood–plastic composites (WPCs) are facing fire hazard when they are used in construction and furniture and need to be treated with fire protection. In this work, polyurethane (PU) was applied to derive simultaneously flame-retardancy-improved and mechanically strengthened wood-polyurethane composites (WPUCs). It was constructed with ammonium polyphosphate (APP) and PU by a simple way. The results showed that a decrease in smoke production in the Cone Calorimeter Test was measured. When the mass of APP is 18% of PU, limiting oxygen index can reach 31.2%. In the combustion test, the peak of heat release rate and total smoke production for WPUCs were, respectively, decreased by 42.1% and 89.7% in the presence of the above ratio of APP and PU. In addition, the results of the functional group test show that PU contains highly reactive -NCO which is bonded to the -OH and moisture in the wood fiber, resulting in improvement of physical and mechanical properties. The mechanism for the flame retardancy of WPUCs revealed that polyphosphoric acid produced by APP pyrolysis catalyzed PU into the char, and PU was arched by the resulting gases such as NH₃ to form the tiny spherical structure, which worked in blocking heat and the exchange of substances. WPUCs with APP prepared by this method are shown to have improved results, and, therefore, it is expected to provide a new strategy for the preparation of flame-retardant WPCs.