USE OF THERMALLY MODIFIED WOOD AFTER THE END OF ITS SERVICE LIFE AS A RAW MATERIAL FOR FUEL PELLET PRODUCTION

The growing demand for environmentally sustainable materials with improved performance has led to a notable rise in the production of thermally modified (TM) wood, including ash wood (Fraxinus excelsior L.). Although TM wood offers enhanced functional properties and durability, it still has a finite service life. Comprehensive experimental investigations have revealed that prolonged environmental exposure (over 24 months) significantly affects the surface quality of thermally modified ash (TM-Ash) wood. Scanning electron microscopy (SEM) identified surface degradation, while water contact angle measurements of indicated a shift from hydrophobic to hydrophilic behavior and accelerated water permeability. As one of the strategies for recycling TM wood at the end of its service life, the potential use of this material as a raw feedstock for solid biofuel production has been explored. The comprehensive thermal analysis of biomass sample (Biom-TM-Ash24) obtained by grinding TM-Ash wood, exposed outdoors for 24 months, revealed its characteristic mass loss behavior across different temperature intervals. The intensive decomposition of hemicellulose, cellulose, and the less stable lignin components, occurring between 200 and 398 °C, was accompanied by the most substantial mass loss (62.9%) and was expressed by a broad extremum on the DTA curve due to the pronounced exothermic reactions, indicating a high calorific value of the biomass. The high calorific value of the biomass (19.7 MJ/kg), which exceeds that of unmodified ash wood biomass (18.8 MJ/kg), along with favorable ash content (0.5–7 wt.% d.m.) and an optimal moisture level (6.8 ± 0.5%), indicates its potential for use as feedstock in solid biofuel production.