A bio-based P/N/S composite intumescent flame retardant for enhancing flame retardancy and smoke suppression of wood flour polypropylene composites

s With growing global resource constraints and environmental concerns, sustainable and eco-friendly characteristics have made bio-based materials the focus of considerable attention. In this work, a novel bio-based composite intumescent flame retardant (SVDP), incorporating P, N, and S as flame-retardant elements, was prepared through Schiff base condensation, addition reaction, and electrostatic ionic interaction, employing phytic acid, vanillin, sulfonamide, and 9,10-dihydro-9-oxa-10-phospha-phenanthrene-10-oxide as precursors. SVDP was introduced into polypropylene-based wood-plastic composites (WFPP) to enhance flame retardancy and smoke suppression performance. Relative to the neat WFPP, the incorporation of 20 wt% SVDP increased the limiting oxygen index (LOI) to 27.2%, while the peak heat release rate (PHRR) decreased by 23.3% and the total heat release (THR) declined by 25.8%. Even at low loadings, SVDP demonstrated notable smoke suppression effects. The flame-retardant mechanism of the SVDP/WFPP system was comprehensively investigated using TG-FTIR, Raman spectroscopy, SEM, and other characterization techniques. By employing a multifunctional bio-based composite flame retardant, this work provides an eco-friendly and efficient strategy to strengthen the fire-retardant performance of wood-plastic composites.