Chemical Elucidation of Structurally Diverse Willow Lignins

Abstract

A new fast-growing wood raw material, willow (Salix matsudana cv. Zhuliu), was subjected to pulping to identify the structure of its lignin. Thus, the black liquor lignin (AL) and enzymatic mild acidolysis lignin (EMAL) were prepared, and their molecular structure and molecular weight of the isolated lignin polymers were comprehensively investigated by Fourier transform infrared spectroscopy (FT-IR), two-dimensional nuclear magnetic resonance (2D-NMR HSQC), 13 C nuclear magnetic resonance ( 13 C-NMR), and gel permeation chromatography (GPC). The NMR results showed that syringyl (S) unit was the predominant structural monomeric unit in willow lignin, as opposed to guaiacyl (G) and phydroxyphenyl (H) units. The S/G ratio for the EMAL was found to be 2.02, whereas that for the AL was 0.94. The lignin in the black liquor (AL) fraction was modified during pulping, as shown by its reduced molecular weight. The two isolated lignin polymers, EMAL and AL showed low weight-average molecular weight: 4127 g/mol and 3522.5 g/mol, and in addition they exhibited low polydispersity index (Mw/Mn < 2.0).

Deep Eutectic Solvents (DESs) for the Isolation of Willow Lignin (Salix matsudana cv. Zhuliu)

“…Zhuliu ) is a new willow variety in the Salicaceae Salix spps., with high planting density, fast growth, strong resistance, and high survival rate, that has been widely applied in wind prevention and sand fixation. Moreover, willow has a good potential for the pulp and paper industry because it is fast-growing, particularly in China [ 4 , 5 ].…”

Willow Lignin Recovered from Hot‐Water Extraction for the Production of Hydrogels and Thermoplastic Blends

“…OÀ H stretch [59,60] 3000-2800 CÀ H stretch in alkanes and alkenes [59,60] 1760-1735 C=O stretch from ester formed by acylation reactions (~1760 -phenolic;~1740 -aliphatic) [61,62] 1710-1690 C=O stretch in ketones, carbonyls, and esters (may originate from carbohydrates). C=O stretch in carboxylic acids and aldehydes.…”

“…C=O stretch in carboxylic acids and aldehydes. [59,60] 1605-1590 aromatic skeletal vibrations plus C=O stretch [59,60] 1515-1505 aromatic skeletal vibrations [59,60] 1330-1320 ring of S-units and condensed G-units [59,60] 1270-1260 ring of G-unit plus C=O stretch [59,60] 1130-1110 aromatic CÀ H in-plane deformation of S-units plus secondary alcohol and C=O stretch [59,60] 1035-1025 aromatic CÀ H in plane deformation, G-> S-units; CÀ O deform in primary alcohols; C=O stretch [59,60] 860-850 CÀ H out-of-plane in position 2, 5, and 6 of G-units [59] the content of free aliphatic and phenolic hydroxyl groups was reduced compared to that of WL. Interestingly, 31 P NMR analysis showed a reduction in the content of aliphatic hydroxyl groups even though the FTIR spectra ( Figure 4) did not show the presence of aliphatic ester linkages at~1740 cm À 1 .…”

Analytical Pyrolysis Characteristics of Enzymatic/Mild Acidolysis Lignin (EMAL)

“…Therefore, in many lignocellulosic biomass transformation technologies, lignin must be removed by pretreatment for the easier and more efficient use of the carbohydrates (Zoia et al 2008;Zheng and Rehmann 2014;Graglia et al 2015;Guo et al 2016).…”

“…Moreover, its macromolecular structure is more intact than industrial and biorefinery lignins and closest to the structure of protolignin. Therefore, EMAL is more representative in the study of the pyrolysis mechanism and product distribution of lignin (Guo et al 2016). Pyrolysis of EMAL isolated from non-wood plants such as bamboo, rice straw, sugarcane bagasse, and corn stalk etc.…”