Flame retardancy of chemically surface-modified hardwoods by electron-beam-initiated polymerisation of impregnated acrylate monomers

Abstract

Monomer impregnation is a great strategy to modify various wood properties. By choosing the right impregnant, it may lead to a higher flame retardancy of treated wood, contributing to its use in specific sectors such as building interior finishes. Yellow birch (Betula alleghaniensis Britt.) and sugar maple (Acer saccharum Marsh.) were surface-impregnated with an acrylate and a phosphorus acrylate monomer under vacuum and exposed to an electron beam for polymerisation. A surface chemical retention of 100 g.m^− 2 was obtained for sugar maple, while the impregnation of yellow birch samples reached one around 200 g.m^− 2. X-ray densitometry confirmed an asymmetric density profile due to the monomer penetration concentrated in the first millimetres of the samples. Microtomography and Raman spectroscopy highlighted the penetration path of the monomers in the wood, mainly through the vessels. The lumens of the cells close to the surface were also filled with polymers. The phosphorus monomer surface impregnation positively impacted the thermal and fire properties of the modified wood. A 25% decrease in the peak of heat release rate was observed, and the residual mass was multiplied by two compared to the reference. The phosphorus monomer contributed to the char formation.