Investigation of structural modification and thermal characteristics of lignin after heat treatment

초록

Milled wood lignin was subjected to heat treatment between 150 and 300 degrees C to understand the pattern of its structural modification and thermal properties. When the temperature was elevated with interval of 50 degrees C, the color of the lignin became dark brown and the lignin released various forms of phenols from terminal phenolic groups in the lignin, leading to two physical phenomena: (1) gradual weight loss of the lignin, up to 19% based on dry weight and (2) increase in the carbon content and decrease in the oxygen content. Nitrobenzene oxidation and C-13 NMR analyses confirmed a cleavage of beta-O-linkage (depolymerization) and reduction of methoxyl as well as phenolic hydroxyl group were also characteristic in the lignin structure during heat treatment. Simultaneously with lignin depolymerization, GPC analysis provided a possibility that condensation between lignin fragments could also occur during heat treatment. TGA/DTG/DSC data revealed that thermal stability of lignin obviously increased after heat treatment, implicating the structural rearrangement of lignin to reduction of beta-O-4 linkage as well as accumulation of C-C bonds. (C) 2014 Elsevier B.V. All rights reserved.

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