Chemical surface densification of hardwood through lateral monomer impregnation and in situ electron beam polymerization, Part II : effect of irradiation dose on hardness, wood chemistry and polymer conversion

Surface chemical densification was recently introduced as a low cost and fast process to improve surface hardness of wood. The asymmetric density profile at the surface due to polymer filled cells was achieved through unilateral impregnation of monomers and their fast in situ polymerization under electron beam radiations. This study investigates the effect of electron beam dose on the newly developed material in order to optimize and increase the performances. Effect of doses from 25 to 125 kGy on wood and polymer in situ were investigated by FTIR spectroscopy, confocal Raman microscopy and GC–MS quantification of extracted residual monomers. Brinell hardness of irradiated controls decreased with increased dose while it remained unchanged for densified samples. The effect of 25 kGy on the irradiated wood controls was insignificant, but evidence of cellulose depolymerization and decrease of hydrogen bonds strength was found at higher dose through FTIR analysis. Raman investigation of the acrylate conversion in situ showed that most of the polymerization was achieved with 25 kGy. Residual monomers were still present in the wood samples up to 100 kGy. Thus, 25 kGy was sufficient to polymerize monomers in situ and increase Brinell hardness of densified wood while avoiding degradation of wood. However, 100 kGy was necessary to ensure highest conversion and no residual monomers. This study is opening perspectives on radiation effects on wood for optimal materials development