In this study, optical behavior of methylated and unmethylated Bjorkman lignin from poplar wood and two lignin model compound (phenolic and non phenolic) with β-O-4 linkages was investigated. First, these lignins were precipitated on a cellulosic matrix (Whatman Paper) using different times (0, 5, 10, 15, 20 h) and then matrixcovered surface was analyzed using Attenuated Total Reflectance FTIR technique. The results showed that irradiation altered the chemical structure of all samples. Lignin

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... s 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.