Research on Thermal Behaviour of Organosolv Lignins Isolated from Fir and Aspen Wood

The composition and thermal behaviour of ethanol-lignins isolated by organosolv extraction from wood biomass of softwood and hardwood species were explored by non-isothermal thermogravimetric analysis (TG/DTG and DSC), FT-IR spectroscopy, elemental analysis, and scanning electron microscopy (SEM). Comparative analysis of IR spectra of the initial lignin and thermally treated lignin at 200 degrees C testifies the identity of their structural-group composition. The initial temperature of decomposition of fir lignin (252 degrees C) is about 10 degrees C higher than that of aspen lignin. It is determined that fir lignin is mainly decomposed in argon within a temperature range of 337-427 degrees C. The maximum degradation rate of the compound is -2.9 %/min; there is the maximal decomposition at 400 degrees C. Aspen lignin undergoes intense decomposition in a lower temperature range (327-400 degrees C) with a maximum mass loss rate of -3.1 %/min at 378 degrees C. Infrared spectral data for products of thermal transformation of fir lignin at 400 degrees C testifies a significant degree of lignin polymer decomposition to likely form guaiacol and phenol derivatives. The completion of thermal decomposition of lignins at 800 degrees C is accompanied by the formation of carbon residues in a 34 % yield of aspen lignin and 37% of fir lignin. The appearance of carbonized particles in the structure of the material, beginning with 240 degrees C followed by intensification of carbon matrix formation with an increase in pyrolysis temperature to 600 degrees C is proven by SEM. It is found that the maximum rates of aspen lignin degradation are higher than those for fir lignin in all conditionally isolated temperature ranges.