Isolation and Characterization of Polyethylene Glycol (PEG)-Modified Glycol Lignin via PEG Solvolysis of Softwood Biomass in a Large-Scale Batch Reactor

We have developed an environmentally benign large-scale (50 kg wood meal per batch) lignin production plant, operating based on acid-catalyzed polyethylene glycol (PEG) solvolysis of softwood biomass. The motivation for the proposed process was to promote technological innovation in biomass utilization systems in Japanese rural areas based on widely abundant Japanese cedar (sugi) biomass. In this study, the process was evaluated by investigating the effects of the source sugi wood meal size and the solvent PEG molecular mass on the yield, chemical structure, molecular mass, and thermal properties of the resultant PEG-modified lignin derivatives, glycol lignins (GLs). Reducing the source wood meal size and PEG solvent molecular mass not only promoted lignin PEGylation but also the subsequent acid-induced chemical rearrangements of the GLs as demonstrated by chemical analyses, 2D NMR, and size exclusion chromatography (SEC). Reducing the source wood meal size and/or increasing the solvent PEG molecular mass enhanced the thermal properties of GLs as determined by thermomechanical analysis (TMA) and thermogravimetric analysis (TGA). We considered that the proposed process can efficiently produce lignin derivatives with substantial control over the chemical structure and thermal properties to meet commercial and industrial needs for lignin-based advanced material production.