Degradation of the Pine Wood Structure in Ozonolytic Delignification

Transformations of pine wood during exposure to ozone were studied. The content of lignin and cellulose in the cellulose-containing material (CCM) from ozonated wood was determined. The polymerization degree (PD) of cellulose from CCM was determined. The CCM samples were examined by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and X-ray diffraction (XRD) analysis. HPLC analysis of water-soluble lignin ozonolysis products was performed. Wood ozonation leads to lignin destruction; 40–42% delignification degree is achieved. The destruction of aromatic components is confirmed by DRIFT spectra. A decrease in the intensity of skeletal vibrations of aromatic ring at 1511 and 1598 cm–1, bands at 1662 cm–1, and an increase in the intensity of stretching C=O vibrations of lignin and hemicelluloses (HCs) at 1736 cm–1 were observed. The stoichiometric ratio of the amount of absorbed ozone and the destroyed guaiacyl units, as well as the composition of water-soluble products, shows that ozonolysis is the main mode of wood lignin destruction. The XRD data and a decrease in PD of cellulose show that, in addition to lignin, HCs and amorphous cellulose are also destroyed during ozonation. It has been found that the region of ozone specific absorption ≤1.5 mmol O3/g corresponds to the most efficient destruction of lignin with the lowest degradation of cellulose fiber.