After cellulose, lignin is, the second most abundant component in wood. In the pulping industry, the introduction of modern Kraft pulping technologies could produce chemical modification in lignin's functional groups. Kraft lignins from Eucaliptus nitens and Pinus radiata industrial black liquors were isolated by acid precipitation. An organosolv lignin was obtained from spent liquor from the P.radiata wood pulping process. All lignins were acetylated with acetic anhydride and characterized by Fourier-transformed infrared spectroscopy (FT-IR). Analysis based on the IR-fingerprint spectral region indicates several differences in the functional groups of the different types of lignins. The thermal behaviour of unmodified and acetylated lignins were studied by differential scanning calorimetry (DSC) and the glass transition temperatures (Tg) were determined and compared with values reported in the literature. The acetylated lignins show a decrease in the Tg values which is probably due, to the at plasticization effect of the acetylation reaction.

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