Quantitative Analysis of the Etherification Degree of Phenolic Hydroxyl Groups in Oxyethylated Lignins: Correlation of Selective Aminolysis with FTIR Spectroscopy

Abstract

PEGylated or oxyethylated lignins (OEL) have recently become a hot topic as precursors for novel lignin-based and sustainable materials or active substances such as hydrogels, aerogels, carbogels, dispersants, and surfactants. Since functional properties of OEL and the resulting materials are strongly affected by the degree of oxyethylation (DOE) of phenolic hydroxyl groups (OHphen), analytical techniques for its determination are crucial. OELs with different levels of modification were obtained by reacting lignins from different pulping procedures with varying amounts of poly(ethylene) glycol-α,ω-diglycidyl ether (PEGDGE). Parent lignins and OELs were characterized by means of selective aminolysis that is subsequent preacetylation and selective deacetylation of aromatic acetates of preacetylated lignin/OEL with pyrrolidine. The reaction product 1-acetyl pyrrolidine was quantified using GC/FID. The DOE of OEL, obtained by subtraction of OHphen content before and after lignin oxyethylation, was found to be...