Carbon Nanostructure of Kraft Lignin Thermally Treated at 500 to 1000 °C

Kraft lignin (KL) was thermally treated at 500 to 1000 °C in an inert atmosphere. Carbon nanostructure parameters of thermally treated KL in terms of amorphous carbon fraction, aromaticity, and carbon nanocrystallites lateral size (L(a)), thickness (L(c)), and interlayer space (d(002)) were analyzed quantitatively using X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy. Experimental results indicated that increasing temperature reduced amorphous carbon but increased aromaticity in thermally treated KL materials. The L(c) value of thermally treated KL materials averaged 0.85 nm and did not change with temperature. The d(002) value decreased from 3.56 Å at 500 °C to 3.49 Å at 1000 °C. The L(a) value increased from 0.7 to 1.4 nm as temperature increased from 500 to 1000 °C. A nanostructure model was proposed to describe thermally treated KL under 1000 °C. The thermal stability of heat treated KL increased with temperature rising from 500 to 800 °C.