Structural Elucidation of Whole Lignin in Cell Walls of Triploid of Populus tomentosa Carr.

To protect adequately the structural features and characterize whole lignin structure of triploid of Populus tomentosa Carr., milled wood lignin (MWL), lignin–carbohydrate complex (LCC), cellulolytic enzyme lignin (CEL), and enzymatic hydrolysis residual enzyme lignin (EHREL) fractions were sequentially isolated from ball-milled wood with mild conditions. The total pure yield of the four lignin fractions could reach up to 92.6% based on Klason lignin content. The structures of the four lignin fractions were quantitatively analyzed. Results showed that the main substructures in the four lignin fractions were β- O -4′ aryl ether and resinol. The LCC fraction contained a high percentage of xylose (96.2%) and numerous β- O -4′ aryl ether linkages (84.4 per 100Ar). The relative high content of phenyl glycoside (PhGlc) linkages between lignin and xylan in the LCC fraction (4.39 per 100Ar) was clearly detected. In addition, some low-molecular-weight lignin fractions were found in the secondary wall. A panorama of whole lignin structure of poplar was proposed.