Thermal stability, degradation kinetics, and molecular weight of organosolv lignins from Pinus radiata

Seventeen organosolv lignin samples were obtained from the black liquor of an ethanol-water treatment using Pinus radiata as raw material under varied conditions applying an experimental matrix designed by employing response surface methodology (RSM). The thermal degradation of lignin samples was studied by a thermogravimetric analyzer (TGA) under an oxidative atmosphere. The thermal stability was estimated by the degradation temperature at 10% conversion (T10%), and the values of the kinetic parameters of the degradation process of lignins were determined using a 3-Gaussian distributed activation energy model (DAEM). The total distribution of the activation energy was obtained, and the mean activation energies of the Gaussian distributions were in agreement with the literature. In addition, the organosolv lignins were characterized by gel permeation chromatography (GPC) to determine their molecular weight distributions. Processing conditions affected the molecular weight of the extracted organosolv ethanol lignins and consequently influenced their thermal stabilities.