Analysis of Photodegraded Lignin and Lignin Model Compounds by ATR-FTIR Spectroscopy

In this study، optical behavior of methylated and unmethylated Bjorkman lignin from populus wood and two lignin model compounds (phenolic and non phenolic) with β-O-4 linkages after transferring on a cellulosic matrice (Whatman Paper) was investigated in different times (0، 5، 10، 15، 20 h). Then paper surface was analyzed using Attenuated Total Reflectance (FTIR) thecnique. The results showed that irradiation altered the chemical structure of all samples. Lignin was the most sensitive component to photodegradation and the intensities of its characteristic bands decreased significantly during the process of irradiation. This was accompanied by formation of new carbonyl groups appearing at 1735 cm_1. Compared with the unmethylated forms، the rate of lignin degradation and carbonyl formation was relatively lower in methylated forms. In other words، methylation of phenolic hydroxyl group reduced the chemical changes induced by irradiation.