Spruce (softwood) and Eucalyptus (hardwood) woods were used as raw material for lignin extraction by organosolv process. Chemical, structural and thermal characterizations of the extracted lignin samples have been performed using HPLC, GPC, FT-IR, P-31 NMR, C-13 NMR, DSC and TGA. Both lignins showed high purity, being Spruce lignin (OS) which presented the highest Klason lignin content (93%) and lowest sugar (0.5%) and sulphur (0.04%) content. Extracted lignin samples were chemically modified with dodecanoyl chloride fatty acid, in order to modify its thermal properties as glass transition temperature (T-g). The noticeable increase in the molecular weight and sharp decrease of T-g can be appreciated. Esterified lignins were used as filler in poly(lactic acid) (PLA) films elaborated by solvent casting in different concentrations (1, 5,10, 25 and 50%). Mechanical, thermal and water barrier properties of prepared films were investigated. The results showed that the addition of both modified lignins contributed to greater ductility and lower stiffness, providing plasticity to PLA. (C) 2016 Elsevier B.V. All rights reserved.