Enhanced mechanical performance and fire resistance of poplar wood: Unilateral surface densification assisted with N/P doped acrylic resin impregnation

It is difficult to significantly improve the mechanical performance and fire-resistance of fast-growing wood without increasing its density. In this study, a modified poplar wood (USD-RA-W) with low-density, high dimensional stability, high mechanical strength, and fire resistance was successfully prepared by unilateral surface densification assisted with the impregnation of waterborne acrylic resin (WAR)/ammonium phytate (APA). The flexural and impact strength values of USD-RA-W increased by 52% and 48%, respectively, compared to the control samples (C-W). The surface hardness and wear resistance of USD-RA-W were also significantly improved, with a 132% increase in hardness and a 22% reduction in weight loss relative to C-W. The improvement in mechanical properties is attributed to the synergistic effects of surface densification and impregnation modification of APA-doped acrylic resin. The in-situ-cured resin network provides excellent dimensional stability by fixing the spring-back of the densified surface of the material. USD-RA-W shows significantly improved fire retardancy due to the introduction of bio-based APA. UL-94 analysis results show that the fire-retardant grade of the USD-RA-W passed V-0 and the limited oxygen index reached 50%. Cone calorimeter test results indicate that the total heat release rate and smoke release rate of the experimental group decreased by 32% and 77%, respectively, while the char residue reached 41%. A simple and green physic-chemical method for the preparation of high-performance USD-RA-W was established in this study. The proposed treated wood may be applicable in structural building materials and interior decoration fields.