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

•Surface densification & impregnation boosted the overall performance of wood.•Modified wood achieved a V-0 grade of fire resistance.•Surface hardness and wear resistance respectively improved by 132% and 22%.•Flexural and impact strength increased by 52% and 48%, respectively.•Modified wood with low density exhibited excellent dimensional stability.