Abstract
Purity, morphology, and structural characterization of synthesized deep eutectic solvent (DES)-lignins (D6h, D9h, D12h, D18h, D24h) extracted from willow (Salix matsudana cv. Zhuliu) after treatment with a 1:10 molar ratio of choline chloride and lactic acid at 120 °C for 6, 9, 12, 18, and 24 h were carried out. The purity of DES-lignin was ~95.4%. The proportion of hydrogen (H) in DES-lignin samples increased from 4.22% to 6.90% with lignin extraction time. The DES-lignin samples had low number/weight average molecular weights (1348.1/1806.7 to 920.2/1042.5 g/mol, from D6h to D24h) and low particle sizes (702–400 nm). Atomic force microscopy (AFM) analysis demonstrated that DES-lignin nanoparticles had smooth surfaces and diameters of 200–420 nm. Syringyl (S) units were dominant, and total phenolic hydroxyl content and total hydroxyl content reached their highest values of 2.05 and 3.42 mmol·g−1 in D12h and D6h, respectively. β-Aryl ether (β-O-4) linkages were eliminated during DES treatment.
Highlights
As a substitute for fossil energy, biomass-based energy has received significant attention over the last decade [1,2]
0.21% of glucose and 0.15% of xylose were present in D12h, suggesting that less carbohydrate remained in the deep eutectic solvent (DES)-lignin at an extraction time of 12 h relative to 6 h, which may be the reason for the increased purity
High purity (90–95.4%) lignin can be obtained from willow
Summary
As a substitute for fossil energy, biomass-based energy has received significant attention over the last decade [1,2]. Zhuliu), among the various biomass resources of interest, is a new hybrid plant variety (Salicaceae Salix spp.) that displays strong resistance and high survival rate. It is widely planted in desert areas for wind prevention and sand fixation. Lignin is one of the three components (cellulose, hemicellulose, and lignin) that make up biomass, and the only fully aromatic polymer found in nature. It is a bio-based raw material attracting intense research in conversion and modification, despite its complex structure [4,5,6]. A variety of isolation technologies have been developed to effect its isolation such as alkaline, enzymatic, and dilute acid hydrolysis, organosolv, ionic liquids, and deep eutectic solvent extraction [7,8,9,10,11,12,13]
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