Condensation of extractive compounds in fresh wood

Previous research shows that phenolic compounds present in xylem sap are susceptible to polymerization in the presence of oxygen. Our aim is to investigate this polymerization and pos-sible condensation in wood matrix: what is the effect on the wood material’s properties?

A single birch tree (Betula sp.) with a diameter of ca. 13 cm was felled in Western Finland in late autumn, immediately packed airtight and stored in a freezer below -18 °C. The wood was ground to a fine sawdust with a hole saw. Two treatments were performed:
1. Fresh Extraction (FE): Sawdust was immediately immersed in a solvent (acetone-water 4:1) in a closed vessel. Extraction was carried out at room temperature (RT; 25 h), then vacuum filtered through a cellulose paper.
2. Dry Extraction (DE): Sawdust was air-dried for 5 days at room temperature, and then ex-tracted (acetone-water 4:1) and vacuum filtered.

Acetone was evaporated under vacuum (25-35 °C). Prior of the freeze-drying the pH of the re-maining water solution was measured. Samples of FE and DE sawdust were compressed into thin disks (diameter ca. 45 mm) for optical measurements. The FE and DE extracts were charac-terized further with UV-vis spectroscopy and GC. The reactivity of the FE and DE samples was tested in autohydrolysis experiments (P factor 800, 150 and 205 °C).

The preliminary results indicate:
• drying of wood prior to extraction caused a distinct yellow hue.
• after autohydrolysis, the Klason lignin content was higher in the dry-extracted wood compared to the fresh-extracted.

The preliminary results suggest that some of the (phenolic) extractive components in fresh birch sap polymerize or condense with other wood components during air-drying. The reaction seems to be irreversible: the colored components cannot be removed with extraction. Details of the chemical changes in the extractive compounds, as well as in the wood matrix, will be reported in the near future, when all the ongoing experiments are finalized.