Flame-retarded, thermoplastic sheets for hot-pressing on poplar plywood: an alternative to thermoset laminates

Abstract As a building material, plywood products must fulfil several requirements such as aesthetic value, durability and good fire performance. To provide these attributes, high pressure laminates (HPL) are often used as top sheets, however, they are difficult to recycle due to their thermoset nature, require adhesives for bonding on wood substrates and are relatively expensive. In this study, thermoplastic sheets based on polylactic acid, polybutylene succinate, wood particles and ammonium polyphosphate were developed and their reaction-to-fire performance evaluated following adhesive-free bonding on poplar plywood. For comparison, plywood impregnated with flame retardants and plywood with flame-retarded HPL were investigated. It was found that the presence of an external top layer, either HPL or thermoplastic top sheets, worsens the fire performance of plywood, increasing heat release and total smoke production. However, plywood with thermoplastic top sheets showed lower peak heat release rate, maximum average rate of heat emission and total heat release than plywood with HPL. Time to ignition was significantly longer for plywood with HPL, and total smoke production was reduced. The results showed that reaction-to-fire performance of plywood with a flame-retarded top sheet is improved compared to HPL, reaching a predicted Euroclass C (EN 13501-1). Overall, the best result (Euroclass B) was obtained for impregnated plywood without any top layer.