Densification of Wood Veneers Combined with Oil- Heat Treatment. Part Ii: Hygroscopicity and Mechanical Properties

In an effort to achieve high mechanical performance and improved dimensional stability, densification combined with oil-heat treatment (OHT) was performed. In our previous study, OHT was successfully applied to densified veneer, which resulted in improved dimensional stability. In the present study, the impact of OHT on densified wood veneer hygroscopicity and mechanical properties was determined. OHT at 180, 200, and 220oC for 1, 2, and 3 hours was applied to densified Aspen (Populus tremuloides) veneers. OHT was found to be an efficient treatment to reduce the hygroscopicity of densified aspen veneers, although OHT had a negative impact on Brinell hardness. However, due to the contribution of densification, the hardness of oil-heat treated veneers was still two to three times higher than that of non-densified veneers. Similar results were found for tensile strength. Bending strength increased slightly at low OHT temperature, and then decreased at high temperature. Bending strength of oil-heat treated densified veneer samples was higher than that of non-densified ones. No significant effect of OHT was found on tensile MOE, but bending MOE increased after OHT. Compared to OHT duration, OHT temperature had a larger impact on densified wood hygroscopicity and mechanical properties.