Chemical and thermogravimetric characterization of chestnut tree biomass waste: towards sustainable resource utilization in the tannin industry

Sweet chestnut (Castanea sativa Mill.) is a key European species, with Italy playing a crucial role in its forest cover and timber production. Chestnut wood processing generates significant residues,with approximately 40% waste at the sawmill stage alone. A major portion of this waste, including that from fruit tree plantations, is used in the tannin extraction industry, exemplifying a circular economy model. This study analyzed exhausted chestnut wood from the tannin industry, virgin wood (prior to tannin extraction), detannized wood (after tannin removal), and chestnut bark, which is separated before the tannin extraction process. The study assessed both the chemical composition and extractives content of the samples. FTIR analysis revealed structural modifications, with key spectral shifts (1640, 1420, 1240, and 1120 cm⁻¹) indicating enhanced aromatic conjugation after extractive removal. TGA analysis showed that detannized wood degraded faster at high temperatures, suggesting better combustibility and biofuel potential, while lignin-rich residues demonstrated greater thermal stability, making them suitable for insulation and biocomposite applications. These findings support optimizing waste utilization, reducing environmental impact, and enhancing resource efficiency. By promoting innovative uses for tannin industry byproducts, this research contributes to sustainability and strengthens circular economy strategies within the forest-wood sector.