Investigation of wood wettability changes during heat treatment on the basis of chemical analysis

Contact angles, measured by Wilelhmy technique, during beech heat treatment by mild pyrolysis under inert atmosphere, indicated a significant increase of wood hydrophobicity for a temperature between 130 and 160 °C. This behaviour, generally reported for higher temperatures, has been investigated in terms of chemical modifications and molecular organization of wood biopolymers to understand the reasons of these hydrophobic properties. Different experiments indicate that degradation reactions and extractives generation are not the origin of these properties. 13C MAS NMR and FTIR analysis suggest that wettability modification during heat treatment could be explained by a modification of conformational arrangement of wood biopolymers due to loss of residual water or more probably to plasticisation of lignin.