Flame-Retardant Performance and Mechanism of Piperazine-Modified APPs on Strandboards

Ammonium polyphosphate (APP) is commercially applied as a flame retardant for wood composites in light-frame constructions. In this work, piperazine (PAz) was utilized to modify APP, i.e., APP-PAz, aiming at a higher flame-retardant efficiency and enhanced mechanical properties. With 10 wt % APP-PAz mixed with wood strands, the limiting oxygen index exhibited an increase of 87.8% compared to the control sample, reaching a value of 42.77%. A 43.8% decrease was observed in the peak heat release rate, while the total smoke emission was reduced by 69.6%. Moreover, for the first time, this study employed thermogravimetric analysis, infrared spectroscopy, and pyrolysis coupled to gas chromatography and mass spectrometry assessments to elucidate the flame-retardant mechanism of APP-PAz. Compared to APP, the gaseous product of APP-PAz enhanced the dilution effect and capture effect, thereby enhancing the gas-phase flame-retardant mechanism. In addition, APP-PAz could improve the efficiency of stress transfer during the three-point bending process, thereby increasing the bending properties. The findings of this study will facilitate the expansion of practical applications for strandboards.