Reactivity of syringyl and guaiacyl lignin units and delignification kinetics in the kraft pulping of Eucalyptus globulus wood using Py-GC-MS/FID

► Pyrolysis was used for the first time to study S and G delignification kinetics. ► Sapwood and heartwood have the same behavior in lignin composition during pulping. ► Reactivity difference of S and G-units is better expressed in later pulping stages. ► Residual lignin composition is independent of pulping time and temperature. ► S/G ratio decreases significantly in the later stages of delignification.