Lignin Derivatives in Beech, Eucalyptus and Oak Wood Hydrochar: Mild Solvolysis and Characterization

This study investigates lignin-derived fractions obtained from the hydrochars of beech (Fagus sylvatica L.), eucalyptus (Eucalyptus camaldulensis) and oak (Quercus cerris L.) following hydrothermal carbonization and mild acidolysis. The aim was to understand the structural, molecular, and thermal properties of the recovered material and to compare how botanical origin influences it. FTIR analysis revealed consistent aromatic signatures across all samples; HP-SEC revealed species-dependent differences in molecular weight distributions, although the overall molecular weight range remained comparable among species; 2D NMR further verified the lignin origin of the isolated fractions, while TGA indicated comparable thermal behaviour among the three biomasses. The whole study shows how hydrothermal carbonization followed by mild solvolysis produces lignin-derivative fractions, highlighting both the potential of this approach for lignin recovery and the need for more efficient methods to obtain higher-integrity lignin suitable for advanced material applications.