Characterization of hydrothermally treated wood in relation to changes on its chemical composition and physical properties

• Hydrothermal treatment of two wood species Monterey pine and English oak.
• Degradation of polyoses and changes in lignin were caused by treatment.
• The main differences between the products of pyrolysis are in relative proportion.
• Hydrophobic effect on surface due to reorientation of functional groups and lignin.

The modification of wood by hydrothermal treatments causes characteristic changes in its chemical composition. The determination of these specific changes was carried out by wet and instrumental chemical analyses. It could be confirmed that the polyoses were the first degraded components in a range from 45.40% to 47.64%. The lignin fraction also showed a significant reduction, increasing with the severity of the treatment, with a degradation rate from 8.65% to 45.39%. Besides, the pyrolysis fingerprints were highly variable due to simultaneous degradation via different pathways as well as to the existence of isomers, and to small structural differences between homologous compounds. Those reactions cause significant physical alterations and wetting phenomena in wood surface with a remarkable hydrophobic effect in modified samples, thus obtaining higher contact angle values than in unmodified samples.