Bio-Based Flame-Retardant and Smoke-Suppressing Wood Plastic Composites Enabled by Phytic Acid Tyramine Salt

Using bio-based chemicals and recycling waste plastics are essential components of the circular economy. Wood–plastic composites (WPCs), fabricated from recycled plastic and wood-processing wastes, are new, green, and environmentally friendly materials. However, their flammability causes potential fire risks and hazards. Although bio-based flame retardants possess the essential advantage over inorganic or petroleum-based chemicals, their application, particularly that of fully bio-based flame retardants, in WPC has been seldom reported. Herein, we designed and synthesized a fully bio-based flame retardant, phytic acid-tyramine salt (referred to as PATA), using a green and environmentally friendly approach with only deionized water as the reaction solvent. PATA is subsequently utilized in conjunction with ammonium polyphosphate (APP) to synergistically impart flame-retardant properties to WPCs. PATA/APP shows a good flame-retardant effect, improving the flame retardant and smoke suppression properties of WPCs. The PATA/APP system can increase the limiting oxygen index by 31% and achieve a vertical combustion V-0 rating. Furthermore, the PATA/APP system can reduce the peak heat release rate, total heat release, and maximum smoke density by 49, 22, and 15%, respectively. The PATA/APP system can generate phosphoric acid substances during combustion, which promote the decomposition of wood flour to form stable char layers containing P–N–C or P–O–C structures. Consequently, we provide an environmental-friendly approach to enhance the flame retardancy of WPCs.