THERMOGRAVIMETRY MASS-SPECTROMETRY OF VARIOUS LIGNOSULFONATES AS WELL AS OF A KRAFT AND ACETOSOLV LIGNIN

Thermal decomposition of kraft lignin, acetosolv lignin and various lignosulfonates has been studied comparatively to a spruce MWL using thermogravimetry/mass spectrometry (TG/MS) in the temperature range from 30-degrees-C to 950-degrees-C in inert gas atmosphere applying 20-degrees-C/min heating rate. The mass of the samples was measured as a function of the temperature and the intensity profiles of 14 molecular and fragment ions of the degradation products (H-2, CH3+, H2O, CO2, CO, CHO+, HCHO, CH3O+, CH3CO+, H2S, CH3S+, SO2, CH3COOH, guaiacol) were simultaneously recorded. Under these circumstances the thermal decomposition of lignins is a relatively slow charring process accompanied by the evolution of high amounts of volatile products with low molecular masses. The amounts of degradation products and their distribution were highly specific for the samples.This can be explained by the differences in the functional groups and ash contents. The presence of organically bonded cations in the lignosulfonates, especially that of sodium, has a major effect on the decomposition mechanism facilitating the dehydration and decarboxylation reactions. Thus, salts of lignosulfontates give rise preferentially to H2O, CO2, CO and to chars with high yield. On the other hand, the evolution of organic gases with low molecular masses is suppressed. TG/MS is well suited to the description of the thermal behaviour of technical lignins.