PHYSICOCHEMICAL CHARACTERISTICS AND THERMOGRAVIMETRIC ANALYSIS OF ALKALI LIGNIN FROM WHEAT STRAW

摘要

The chemical and structural compositions of the pure technical alkali lignin from wheat straw (AlL) were determined by elemental analysis, scanning electron microscope, GPC, ~1H-NMR and alkaline nitrobenzene oxidation. The pyrolysis properties of AlL were analyzed by thermogravimetry (TGA). It was found that the average molecular of AlL was 4413 (Mn), the C_9 unit was C_9H_(8.22)O_(2.53)(OCH_3)_(0.66). The ~1H-NMR spectra and the results from alkaline nitrobenzene oxidation revealed that AlL was a kind of highly condensed GS lignin with low contents of acidic functional groups and methoxyl group. The thermogravimetric analysis indicated the maximum degradation rate was reached at a temperature of 309.2℃, when the temperature reached 650℃, the weight loss of AlL in atmosphere of flowing nitrogen was found to be 53.1%, and when the temperature reached 780℃, the weight loss was 65.3 %.