Effect of steaming and furfuryl alcohol impregnation pre-treatments on the spring back, set recovery and thermal degradation of densified wood of three tropical hardwood species

Alnus acuminata, Vochysia ferruginea and Vochysia guatemalensis, low-density species, have been previously studied due to their potential in the thermomechanical densification process. However, their spring back and set recovery values are reported to be high. Therefore, the objective of this work was to investigate and evaluate the effects of steaming and furfuryl alcohol impregnation pre-treatments on the spring back, set recovery, and thermal degradation of densified wood of these three tropical hardwood species. The results indicate that both steaming and furfurylation pre-treatments improved the dimensional stability of the densified wood of these three species. The wood densified with furfurylation pre-treatment presented higher spring back values (greater than 3%) but lower set recovery (lower than 5%) than wood densified with steaming pre-treatment. In addition, compared with the un-densified wood, the DTG/TG curves of the three species showed that the furfurylation-pre-treatment presented thermal stability and chemical modification related to the structure of hemicelluloses and the amorphous zones of cellulose and lignin, which was confirmed by the FTIR spectrum. In the wood densified with steaming pre-treatment, a modification of hemicellulose was evident in the FTIR data, resulting in a displacement of the curve that was only observed at higher temperatures, making it more thermally stable. The densified wood of V. ferruginea and V. guatemalensis presented lower spring back and set recovery values in comparison to the wood of A. acuminata regardless of the treatment applied, suggesting that these two species present better conditions for the densification process.