Structural and Morphological Transformations of Lignin Macromolecules during Bio-Based Deep Eutectic Solvent (DES) Pretreatment

2020 
Elucidating the structural characteristics and changes of lignin during biorefinery is considerably important for lignin valorization. To examine the structural transformations of lignin under deep eutectic solvent (DES) pretreatments, the double enzymatic lignin (DEL) isolated from Eucalyptus was pretreated with DES (ChCl/lactic acid, 1:10) under the conditions of 60–140 °C for 6 hours. The structural transformations of lignin during the DES pretreatment have been investigated by quantitative 13C-NMR, 2D-HSQC NMR, 31P-NMR, GPC, and SEM techniques and the lignin degradation products recovered after DES pretreatment have been analyzed by GC-MS technique. NMR results demonstrated that the dissociation of aryl ether linkage (i.e., β–O–4) is dominant during the DES pretreatment, which is in line with the increased content of phenolic hydroxyl in these lignins. In addition, the decreased aliphatic hydroxyl groups suggested that acylation or dehydration of aliphatic hydroxyl groups occurred as the pretreatment ...
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