Fractionation and Characterization of Glycol Lignins by Stepwise-pH Precipitation of Japanese Cedar/Poly(ethylene glycol) Solvolysis Liquor

Abstract

Recently, we have demonstrated the initial process design of acid-catalyzed poly(ethylene glycol) (PEG) solvolysis of softwood Japanese cedar (JC) in a large-scale batch reactor (50 kg wood meal per batch) to produce PEG-modified glycol lignins (GLs) as a potential feedstock for high-value-added applications. Typically, GLs were produced by acidification (pH 2) of the alkaline JC/PEG solvolysis liquor (pH 11) obtained after the solvolysis reaction using three kinds of JC wood meal sizes (average meal size, JC-L (1.6 mm) > JC-M (0.8 mm) > JC-S (0.4 mm)) and PEG solvent molecular masses (PEG200 < PEG400 < PEG600). In this study, stepwise-pH precipitation (pH 11–8–6.5–4.5–2) was conducted using a JC/PEG solvolysis liquor to further understand the characteristics of bulk GLs. Notably, the molecular weight-dependent fractionation of four GL fractions was obtained with different fractional yields. Consequently, the contents of intermonomeric linkages and functional groups slightly varied according to the fractionation pH while exhibiting a similar chemical structure and thermal behavior to the corresponding bulk GLs. The overall thermal analysis data suggested that bulk GLs prepared from PEG400 solvolysis processes are suitable for the fabrication of melt-processed materials, such as fiber-reinforced plastics (FRPs), automobile parts, and speaker cones.