AbstractThis study investigated alterations in the lignin of pinewood (Pinus sylvestris L.) during heat sterilization. The Klason lignin content was determined, and the dioxane lignin was isolated. Changes in the dioxane lignin were evaluated by size exclusion chromatography (SEC) as well as Fourier transform infrared (FTIR) spectroscopy. The analyses illustrated an increase in the percentage of extractives and the amount of dioxane lignin yields, while a decrease in the acid-insoluble lignin content was also observed. Changes in the macromolecular characteristics of the dioxane lignin (molecular weight and polydispersity) were not significant (p < 0.05); however, they indicated that simultaneous degradation and condensation reactions had occurred. The FTIR spectra of the dioxane lignins showed an increase at 3420 cm-1 (O-H stretching vibration), indicating the cleavage of ether bonds. The band at 1715 cm-1 (unconjugated C=O stretching) increased after an initial decrease due to the cleavage of the β-alkyl-aryl ether bonds. Also, the band at 1660 cm-1 (conjugated C=O groups) increased, which was caused by the cleavage of the α-alkyl-aryl ether bonds.