Analysis of Structural Units and Their Influence on Thermal Degradation of Alkali Lignins

Abstract

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%.

Physicochemical Characterisation of Technical Lignins for Their Potential Valorisation

“…Also, at this point, the higher cross-linking capacity of alkali lignin at 600°C can be observed, displaying the higher H structures content comparing to the LignoBoost sample. For the sake of application purposes, these results show the potential of both lignins valorisation towards producing bio-oil [29] or biomaterials [30], for example, and biological conversion due to application at mild conditions. In contrast, they do not provide good candidates for phenolformaldehyde resin synthesis, as the maximum rate loss within the nonmodified resins appears at 345°C [22] or other adhesives [31].…”

An alkaline deep eutectic solvent based on potassium carbonate and glycerol as pretreatment for the isolation of cellulose nanocrystals from empty fruit bunch

“…The degradation of lignin happened concurrently with other degradation processes and may have remained as a residue at the end of degradation, ranging from room temperature to 700 °C, as shown in region C (Sabaruddin and Paridah 2018). This was due to the complex structure of lignin that made up of the aromatic rings with numerous branches (Hua et al 2016). At the temperature range between 400 ℃ to 600 ℃, a shoulder peak was observed for all cellulose samples.…”

Characterization of Thermo-Chemical Degradation and Pyrolysis Properties for Three Kinds of Biomass Residues

“…The intensities of WSS and PSS were stronger than SSS. One possible explanation is that the absorption intensity (C=O in unconjugated carbonyls stretching) of wood lignin is more observable than that of non-wood lignin, and the chemical structure of WSS and PSS is similar to that of coniferous wood (Hua et al 2016). The infrared bands of WSS and PSS at 1512 cm −1 (assigned to the aromatic skeletal in lignin) were stronger than SSS.…”

“…This was probably due to their basic structures, which were mainly composed of guaiacyl propane. Furthermore, the common types of interunit linkage in lignin are α-O-4, β-O-4, and 4-O-5 bonds, which could easily produce guaiacol in the lignin degradation process (Hua et al 2016). Moreover, nitrogen compounds (pyrrole 1.67%, acetamide 1.19%) were identified in the bio-oil from PSS.…”