Effect of modification on mechanical property and fire-retardantbehavior of fast-growing poplar wood

Fast-growing poplar wood was modified with boric acid phenol formaldehyde resin (BPF) at different concentrations. In comparison with structural Douglas fir and Chinese fir, the effect of modification on the mechanical and burning behavior of poplar wood was studied. The results show that the strength level of poplar wood cannot meet the demand of related standards. The modified poplar wood with 20% BPF reaches TB11, and both 30% and 40% BPFpoplar wood reaches TB13. The oxygen indexes of 20%, 30% and 40% BPF-poplar wood increase by 97.37%, 113.68% and 128.42%, respectively. Poplar wood shows higher heat release rate (HRR), total heat release (THR) and production rate of CO₂ (PR-CO₂) than both Douglas fir and Chinese fir. The BPF modification can effectively reduce the combustibility and delay the ignition time of poplar wood, and that higher BPF concentration has a better fireretardant behavior. The HRR peak value of 40% BPF-poplar wood is reduced by 31.22%, which is 14.33% higher than that of Douglas fir. The THR value of 40% BPF-poplar wood is similar to that of Douglas fir. The PR-CO₂ peak value of 40% BPF-poplar wood is reduced by 30.57%, which is 6.01% higher than that of Douglas fir. The residual weight of 40% BPF-poplar wood is increased by 64.83%. Its burning behavior reaches and even is higher than the level of conventional building structural wood materials.