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 (d₀₀₂) 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 d₀₀₂ 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.