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The chemical structures of four alkali lignins isolated from poplar, fir, straw, and bagasse were investigated. To explore the relationship between the structural units and the thermal decomposition behavior, the system was tested by elemental analysis, Fourier transform infrared spectrometry, thermogravimetric analysis (TGA), and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The results indicated that the carbon content of poplar lignin (PL) was higher than that of others. Fir lignin (FL) exhibited the highest guaiacol units, while the other three lignins were abundant in syringol units. The thermal decomposition characteristics and pyrolysis products of the four lignins were influenced by the material structural and composition. The DTG curves showed that the initial temperatures and major degradation temperatures of woody lignins(FL and PL) with complex inherent structures were shifted to the high temperature zoom compared with that of non-woody (BL and SL) lignins. Py-GC/MS analysis showed that guaiacol-type phenolic compounds were predominant pyrolysis products derived from the four lignins. The yield of guaiacol-type phenols could reach 82.87%. Moreover, the BL had selectively on phenol-type compounds with yield of 27.89%. [ABSTRACT FROM AUTHOR]

In this study, two purified mild acidolysis lignins (MAL) extracted from triploid poplar, i.e., Alcell MAL and Alkali MAL, were compared. Some properties, including elemental contents, higher heating value (HHV), functional hydroxyl group compositions, and molecular weights, were tested to characterize the structure of these two MALs. The releasing laws of gases and the distribution of products were also investigated through the use of thermogravimetric Fourier transform infrared (TGFTIR) and pyrolysis-gas chromatography combined with mass spectrometry (Py-GC/MS). The results showed that both MALs had pyrolytic advantages, largely because of their unique chemical structures. However, although the species of volatiles from Alkali MAL were similar to those from Alcell MAL, the releasing temperature range for Alcell MAL was relatively narrow and the volatiles from it were concentrated. Among the fast pyrolytic products, phenols were the most abundant. The yield of 2,6-dimethoxy-4-(2-propenyl)phenol, which was the dominant product, was 25.66% for Alcell MAL and 20.77% for Alkali MAL, respectively. Overall, pyrolytic products from Alcell MAL were more enriched. [ABSTRACT FROM AUTHOR]

In the present work, three different kinds of lignin fractions (L1, L2, and L3) were isolated from the alkali black liquor of Cunninghamia lanceolata by selective precipitation at the pH values of 8 (fraction L1), 5 (fraction L2), and 2 (fraction L3). Elemental analysis, gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT-IR), 31P nuclear magnetic resonance (31P-NMR), thermal gravimetric analysis (TG), and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) were used to characterize the chemical structure and thermochemical properties of the three lignin fractions. The results showed that L1 presented higher heating value (HHV) and molecular weight compared with L2 and L3. The structures and functional group types were similar for the three lignin grades. However, there was more hydroxyl group in L1 than that in L2 and L3, and the L3 contained a higher amount of carboxylic hydroxyl. L1 exhibited the lowest weight loss value (47.8%) at 200 to 600 oC and the highest amount of charred residue (45.1%), which was exactly the opposite for L3. Phenols, the dominant pyrolysis products, constituted 92.17% of all the pyrolysis products for L1, 93.93% for L2, and 88.09% for L3. [ABSTRACT FROM AUTHOR]