Characterization of lignins from the black liguor of Australian eucalyptus kraft of the nail
Lignin samples were separated from the black liquor of Australian eucalyptus kraft pulping by ethanol-acid precipitation or acid precipitation. Elemental analysis, FT-IR, and 1H NMR were conducted to compare their structural characteristics. The thermal behaviors were studied by TGA and heating value was examined with oxygen bomb calorimeter. The obtained C9 expanded formulas for acid-extraction lignin and ethanol-acid-extraction lignin were C9H9.52O2.96 and C9H9.58O3.18, respectively. According to FT-IR and 1H NMR analyses, the two lignins were similar to hardwood lignin of type GS. However, the acid-extraction lignin showed a high proportion of syringyl (S) unit. TG results showed that degradation process of the two lignins was similar, but their degradation temperatures were different. The weight loss rate reached its maximum value of 8.49 wt% / °C and 4.39 wt% / °C for ethanol-acid-extraction lignin and acidextraction lignin, whose temperature of maximum weight loss was 371°C and 356°C respectively. Results of oxygen bomb calorimeter tested showed the incendiary heat of ethanol-acid-extraction lignin was higher than that of acid-extraction lignin.