Evaluation of the structure and acid-base properties of bulk wood by FT- Raman spectroscopy

The structure of pine wood (Pinus silvestris L.) has been analyzed by FT-Raman spectroscopy, taking birch wood and the wood components cellulose, hemicellulose (xylan), and lignin as well as previously characterized wood resins as references. The acid-base properties of bulk pine wood were evaluated by comparing the spectra recorded before and after the treatment with various solvents. After the treatment with the probe liquids having only a Lifshitz-van der Waals (LW) component, it was found that the LW interactions in pine wood take place without changing the main structure. After treatment with Lewis acid-base active probe liquids, the spectra indicate that, e.g., the intense peak located at ~2936 cm-1 (CH2 stretch) seems to disappear, suggesting that this peak may be related to Lewis acidity. In addition, after treatment with a Lewis acid, it was found that the intense peak located at ~1657 cm-1 (C=C) is shifted, relating to Lewis basicity. With the ratio ~2936/~1657 cm-1 as a measure of the acid-base properties of bulk wood, a value of about 2.00 indicates that the bulk pine wood is largely acidic. The pH determined supports the evaluation made by FT- Raman spectroscopy.