Deciphering the nonlinear variation of subunits during the delignification of bamboo

Abstract

In-depth analysis of the structural evolution of lignin during fractionation is imperative to understand its physicochemical properties, which are essential for its efficient valorization. The organosolv pretreatment of lignocellulosic biomass can realize lignin regeneration and extract higher purity lignin. However, the detailed structural evolution mechanism of lignin separation during the organosolv pretreatment is currently lacking. In this work, bamboo lignin was extracted as a function of time under alkaline organosolv pretreatment to uncover its structural evolution mechanism. In this pretreatment system, the extracted lignin had a lower molecular weight, which was beneficial for downstream applications. The results showed that the content of resinol (β-β), phenylcoumaran (β-5) and α,β-diaryl ether linkages varied nonlinearly. This was attributed to the simultaneous occurrence of fractionation, depolymerization and condensation under multi-rate control. In the validation experiments, when there was no solvent-promoted depolymerization and repolymerization in lignin, or no new lignin fragments were introduced in the reaction, the subunit content of lignin was controlled by a single rate, i.e., the subunit content changed monotonically. Overall, this study provides a theoretical basis for the efficient utilization of lignin and high-value conversion of bamboo.