Wood densification and thermal modification: hardness, set recovery and micromorphology
The density of wood can be increased by compressing the porous structure under suitable moisture and temperature conditions. One aim of such densification is to improve surface hardness, and therefore, densified wood might be particularly suitable for flooring products. After compression, however, the deformed wood material is sensitive to moisture, and in this case, recovered up to 60 of the deformation in water soaking. This phenomenon, termed set recovery, was reduced by thermally modifying the wood after densification. This study presents the influence of compression ratio (CR 40, 50, 60 and thermal modification time (TM 2, 4, 6 h) on the hardness and set recovery of densified wood. Previously, set recovery has mainly been studied separately from other properties of densified wood, while in this work, set recovery was also studied in relation to hardness. The results show that set recovery was almost eliminated with TM 6 h in the case of CR 40 and 50 Hardness significantly increased due to densification and even doubled compared to non densified samples with a CR of 50 Set recovery reduced the hardness of densified (non TM) wood back to the original level. TM maintained the hardness of densified wood at an increased level after set recovery. However, some reduction in hardness was recorded even if set recovery was almost eliminated.
Wood Science and Technology