Characterization of Natural and Technical Lignins using FTIR Spectroscopy

Characterization of lignins is an extremely difficult task because of their diversity in respect both to source and extraction method. In the present work, the possibility to use infrared spectroscopy instead of chemical analysis to characterize the changes in the functional groups of lignin during cooking was evaluated and a library of infrared spectra from different lignin samples was created. Lignin samples from different sources were obtained under different cooking conditions and the structure of the functional groups of the samples were determined by both chemical methods and infrared spectroscopy. Two different types of cooking procedures were carried out resulting in 24 lignin samples. The changes in the functional groups during cooking were determined and analysed and the results obtained with chemical- and spectroscopic methods were compared. The results of the work shows that, with the methods employed in the present work, it is not possible to use infrared-spectroscopy instead of chemical analysis to characterize the changes in the functional groups of lignin during cooking.