Evaluation of chemical densification of three hardwood species through in-situ electron beam polymerization
J Triquet, P Blanchet, V Landry
Hardwoods are the most suitable species for wood flooring for their appearance as well as their hardness. Yet, improving hardness can provide substantial benefit for the wood flooring market. Chemical densification of wood and in-situ polymerization through electron beam technology was chosen to increase hardness of three hardwoods (Yellow birch (YB) (Betula alleghaniensis Britt.), Sugar maple (SM) (Acer saccharum Marshall) and Red Oak (RO) (Quercus rubra L.)). Monomer formulations were chosen for their viscosity. Impregnation was carried out through a simple vacuum process and was followed by 100 kGy electron beam irradiation to allow in-situ polymerization. Successful polymerization was proved by infrared spectroscopy and thermogravimetric analysis. Chemical retention and hardness of densified and reference samples were measured. Chemical retention (CR) varied between the three species being the lowest for porous red oak and the highest for diffuse porous yellow birch. CR also decreased with increasing viscosity of the impregnant for SM and YB. However, viscosity did not affect chemical retention of RO samples. Hardness of wood increased substantially for all treatments and all species and was comparable to that of Jatoba. Densified YB samples showed greater improvement of hardness compared to RO and SM due to higher chemical retention. Results also showed that with low chemical retention, hardness was improved but densified wood hardness is mostly influenced by wood properties. While the three species showed significant hardness improvement, yellow birch seems more suitable for densification.
Keywords: densification, electron beam, acrylate, viscosity, impregnation, hardness