Study on the Flame Retardant Properties of Poplar Wood Treated with Sodium Phytate and Metal Ions

Poplar wood was impregnated with PA-Na, metal ions (Al³⁺/Mg²⁺/Ca²⁺), and an alkaline solution. The morphological structure and elemental distribution of the treated wood were characterized by scanning electron microscopy (SEM), infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Flame retardancy was evaluated using limiting oxygen index (LOI) and vertical burning tests (UL-94), while thermal stability and combustion behavior were investigated by thermogravimetric analysis (TGA) and cone calorimetry. The results showed that the LOI of the modified wood increased from 19.6% to 36.5% with increasing metal ion concentration, reaching an optimum at 20% and achieving a V-0 rating in the UL-94 test. TGA revealed that the flame retardant treatment reduced the initial decomposition temperature and accelerated the pyrolysis rate. Cone calorimetry results indicated that the total heat release (THR) of wood treated with PA-Na with 20% Al³⁺, Mg²⁺, and Ca²⁺ decreased by 13.37%, 14.80%, and 10.24%, respectively. Moreover, the smoke release rate (TSR) and CO₂ emission were suppressed during the early combustion stage. Residual char analysis confirmed that the synergistic interaction between PA-Na and metal ions promoted the formation of a protective char layer, effectively preserving the wood structure and permeability and significantly enhancing flame retardancy.