The evolution of teak extractives under UV exposure and their impact on wood surface properties

UV irradiation accelerates lignin photodegradation and drives rapid deterioration of wood surfaces, severely limiting outdoor service life. Teak, a naturally durable species, contains extractives that may provide intrinsic photoprotection. In this study, natural extractives were removed from teak using Soxhlet extraction. The unextracted and extracted samples were irradiated with UV for 576 h, after which their surface properties were evaluated and the corresponding extractives were analyzed by GC-MS. This study aimed to assess the protective effects of extractives against wood photodegradation and to elucidate their transformation mechanisms. Results showed that the extracted group experienced more severe photodegradation: greater colour change (ΔE = 22.47) compared to the unextracted group (ΔE = 12.94), increased surface roughness and hydrophilicity, and more pronounced chemical oxidation. GC-MS analysis revealed that after 576 h of UV irradiation, squalene disappeared completely from the teak extractives (compared to 38.62 % before irradiation), and the content of 2-methylanthraquinone decreased from 20.16 % to 11.47 %. Mechanistically, squalene acts as a singlet-oxygen quencher with antioxidant effects, whereas anthraquinone derivatives serve as competitive UV absorbers that delay lignin photodegradation. Overall, teak extractives significantly mitigate UV-driven surface deterioration, highlighting their potential as eco-friendly and efficient photostabilizers for wood. • An integrated physical, chemical, and microscopic analysis reveals the role of teak extractives in surface photodegradation. • The presence of extractives significantly improves the photostability of wood surfaces under UV exposure. • Squalene, a key component of teak extractives, protects lignin from photodegradation by quenching singlet oxygen. • Quinones in teak extractives delay the photodegradation of lignin by absorbing UV light.