Investigation of Structural Modification and Thermal Characteristics of Lignin after Heat Treatment.

International journal of biological macromolecules

PubMedID: 24530642

Kim JY, Hwang H, Oh S, Kim YS, Kim UJ, Choi JW. Investigation of Structural Modification and Thermal Characteristics of Lignin after Heat Treatment. Int J Biol Macromol. 2014;.
Milled wood lignin was subjected to heat treatment between 150 and 300°C to understand the pattern of its structural modification and thermal properties. When the temperature was elevated with interval of 50°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 ans (13)C-NMR analyses confirmed a cleavage of ß-O-4 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 ß-O-4 linkage as well as accumulation of C-C bonds.