Research on mechanical properties and fire resistance of flame- retardant laminated veneer lumber fabricated with fast-growing Poplar

Abstract

To fully utilize Chinese fast-growing timber resources, fast-growing poplar was selected for manufacturing flame-retardant laminated veneer lumber (FRLVL). Firstly, orthogonal experiments were conducted to assess the impact of four factors (hot-pressing time, hot-pressing temperature, retardant concentration, and retardant types) on the mechanical properties and burning behavior of FRLVL. Subsequently, optimal manufacturing parameters were chosen based on statistical analysis. Finally, the fire performance of LVL manufactured with the optimal parameters was evaluated to investigate changes in physical-mechanical properties under high-temperature conditions. Results indicated that the addition of retardants led to a decrease in mechanical properties. In comparison to the control group, LVL composites impregnated with two retardants exhibited a higher limited oxygen index and longer fireproof time, with the effects of ammonium polyphosphate (APP) surpassing those of borax (BX). The optimal manufacturing parameters were a hot-pressing temperature of 140°C, a hot-pressing time of 1.3 min/mm, and concentrations of 15% for both retardant types. As the temperature increased, the mechanical properties of LVL manufactured with the optimal parameters decreased noticeably. However, under the conditions of a temperature of 200°C and a treatment time of 90 min, the mechanical properties of LVL composites still met the LVL-32P grade proposed in LVL handbook.