Structural conversion and characterization of Camellia oleifera shell lignin based on mechanochemical-assisted pretreatment

Abstract

Camellia oleifera shells (COS), are the by-product of Camellia oleifera seed oil processing, and possess a high lignin content (38.6%). However, information on the fundamental chemistry of this lignin is limited. Herein, mechanochemical strategies combining ball-milling with mild acetosolv or alkaline treatment are presented to compare the structural evolution of COS lignins. The mechanochemical processes significantly improve the lignin yield, releasing lignins with high molecular weights (Mw ≈ 7000 mol/g). The COS lignins are GS-type lignins, and G units account for 71.9% of MWL. The synergistic combination of ball-milling and acetosolv treatment led to the cleavage of β-O-4 linkages. In contrast, the alkaline lignin fractions retained a large number of β-O-4 linkages (50.67/100 Ar) and a low phenolic OH content (1.56 mmol/g), indicating that the ball-milling process had little effect on the alkaline lignin structures (typical substructures). In summary, understanding the structural conversion and characteristics of lignins during the combined pretreatments of COS would facilitate the optimization of the pretreatment process and the deconstruction of COS.