Flame-Retardant Wood Scrimber/Plywood Composites: Preparation, Characterization, and Enhanced Structural Performance

Veneer-based wood composites are widely used for interior applications, yet their high flammability and smoke emission significantly limit their safe use in buildings. In this study, a multifunctional flame-retardant polyethylene adhesive film was developed via melt blending and hot pressing of a mixture of amino trimethylene phosphonic acid (ATMP), hydroxyethylidene diphosphonic acid (HDEP), melamine (MEL), and sodium alginate (SA). This film was laminated onto veneers to fabricate flame-retardant decorative plywood. Simultaneously, wood scrimber units for structural applications were prepared by impregnating wood with a flame-retardant system consisting of sodium silicate (Ss) and sodium tetraborate (St). These treated components were integrated to form a flame-retardant wood scrimber/plywood composite (AHM-S), with the wood scrimber as the core layer and the treated plywood as surface layers. Compared to the control, the AHM-S composite showed a 44.1% reduction in the second peak heat release rate (pk-HRR2), a 22.6% decrease in total heat release (THR), and a 12.7% reduction in maximum flame spread distance (MD_300°C). Moreover, the time to reach 275 °C on the unexposed side (T_275°C) was extended by 90.2%. These improvements are attributed to the synergistic flame-retardant effects of the surface film and impregnated core, which jointly suppress flame spread and delay thermal degradation. The composite demonstrates promising fire safety and mechanical performance for engineered wood applications.