The analysis of st acetone soluble st Acetone solubles were
2nd-acetone-solubles were analyzed by TGA, CHNS elemental analysis, thermomechanical analysis (TMA) and GPC. Fig. 8 shows the pyrolysis profiles of samples analyzed by TGA. All the profiles were very similar to that of organosolv lignin. 2nd-acetone-solubles of cedar and rice straw decreased the yields of char closer to that of organosolv AG 1879 by the 2nd treatment comparing with those of 1st-acetone-solubles, which meant acetone-solubles were converted into lignin-purer components by the 2nd treatment. 2nd-acetone-soluble of beech lowered its decomposition temperature. Among the main components of biomass, hemicellulose shows the lowest decomposition temperature (about 180 °C) and lignin shows the highest decomposition temperature (about 280 °C), which confirms the assumption discussed in the previous section that some of 1st-water-solubles (hemicellulose derivatives) of beech were converted into acetone-soluble components by the 2nd treatment. The elemental compositions of samples were analyzed by CHNS elemental analysis, and the results are shown in Table 2. All the samples increased carbon contents and decreased oxygen contents from 1st-acetone-solubles. Oxygen content is generally estimated to increase by hydrolysis, however, the carbonation at high temperature had a bigger effect in this reaction. About ash, all the samples contained none of that anymore after the 2nd treatment. Next, the softening temperatures of samples were measured by TMA. The results are listed in Table 4. The softening temperatures of 1st-acetone-solubles of all samples were very different, and high in order from cedar, beech, to rice straw. This difference was because of the difference in constituents of lignin, and the hemicellulose derivative in 1st-acetone-solubles. All the samples lowered the softening temperatures remarkably by the 2nd treatment, which indicated that extracted lignin was depolymerized well. To confirm this, the MWDs of 2nd-acetone-solubles were analyzed by GPC. The results are shown in Fig. 9 with those of 1st-acetone-solubles. The black solid lines and the gray broken lines are, respectively, for 2nd-acetone-solubles and 1st-acetone-solubles. The base lines were shifted for each type of biomass sample. For the relative evaluation by the intensity, 10 mg of each acetone-soluble was dissolved in 5 mL of acetone before the analysis. All the samples increased the intensity of the lower molecular weight fractions of Mw < 1000 by the 2nd treatment. The peaks of the fractions of Mw > 1000 of 1st-acetone-solubles of cedar and rice straw were shifted to lower molecular weight area. 1st-acetone-soluble of beech, different from the other samples, did not have peaks of the higher molecular weight fraction. This was probably because acetone-soluble was actually obtained as “water-insoluble components” in this experimental method, and 1st-acetone-soluble of beech could not be completely dissolved in acetone before the analysis by GPC. Some insoluble fractions were actually recognized in the solution of 1st-acetone-soluble of beech, which supported this assumption. Those insoluble fractions were depolymerized by the 2nd treatment and, converted into acetone-soluble components. As a summary, the acetone-soluble components of all the types of biomass were converted into depolymerized lignin of Mw < 1000 fractions by the 2nd treatment.