Improvement of fire retardancy of plywood by incorporating boron or phosphate compounds in the glue

A practical approach to enhancing the fire retardancy of wood-based materia ls by adding fire-retardant chemicals to the glue was developed. Plywoods w ere manufactured using urea melamine formaldehyde resin mixed with ammonium pentaborate or dihydrogen phosphate. Treated plywoods had better incombust ibility than untreated ones. X-ray photoelectron spectroscopy (XPS) analysi s clearly demonstrated the distribution of boron and phosphorus, which had migrated from the glue to the wood, contributing to better fire retardant p roperties. The cross-sectional micrographs from scanning electron microscop y showed that untreated specimens exhibited a foamy structure near the inte rface in the glue layer and the deformed structure of wood cells. The cell structure and cell wall thickness retained intact in the specimens treated with urea melamine formaldehyde resin mixed with ammonium pentaborate or di hydrogen phosphate. When observing the effect of the thickness of overlay v eneers on incombustibility, a shorter glowing time was obtained from the sp ecimens with a thicker surface layer when the fire retardant chemical was a dded at 2%, but the differences were smaller at the higher chemical retenti on of 4%. A similar tendency was observed for the char length.