Isolation and Thermal Characterization of Softwood-Derived Lignin with Thermal Flow Properties

A potential alternative biorefinery platform, in which high quality lignin is the main product of the process, is demonstrated. The polyethylene glycol (PEG)-modified softwood lignin (glycol lignin, GL) was isolated from Japanese cedar by acid-catalyzed PEG solvolysis, where liquid PEG with varying polymer chain length was used as the solvolysis reagent with a small amount of acid catalyst. The isolated glycol lignin had the weight-average molecular weight of 4000-7000 and exhibited a viscous thermal flow property, which is impossible for industrial softwood lignin without further processing steps. Thermal analyses, such as thermomechanical analysis (TMA) and capillary flow tester rheometer (CFT), proved to be sensitive techniques for determination of thermal flow behavior. The lignin yield and solid residue (mostly cellulosic residue), respectively, of 28%-31% and 36%-38% (dry wood basis) were obtained from PEG200 solvolysis with 0.5%-0.7% acid catalyst. The results indicated the effectiveness of the one-step PEG solvolysis process to separate glycol lignin and cellulosic residue. The present approach is promising for the quest of high purity lignin production with specified thermal properties.