Study of new chemical derivatization techniques for lignin analysis by size exclusion chromatography

Lignin is the second most abundant biopolymer on earth and it consists of highly-branched, three dimensional aromatic structures with variety of functional groups, mainly phenolic and alcoholic functions. This research work was focused on derivatization methods to quantify hydroxyl groups in lignins and to determine lignin molar mass distribution by size-exclusion chromatography coupled to multi-detectors. Five different technical lignins were studied: Protobind 1000, Organosolv (CIMV), Pine Kraft, Eucalyptus Kraft and Indulin. Lignin samples were washed and derivatized by classical acetylation, which was compared to fluoro-derivatization using the new methods developed in this work, such as fluorobenzylation and fluorobenzoylation. Hydroxyl groups present in the lignin samples were quantified by potentiometric and conductometric titrations, GC-aminolysis, IR and differential UV spectroscopies and NMR spectroscopy (1H, 13C, 19F and 31P). Molar mass distributions of derivatized lignins were calculated using different columns and solvents (DMAc and THF). Conventional calibration, using different standard polymers as calibrants, was compared to the so-called “universal calibration method”, which uses viscometric and refractometric detectors. Fluoro-derivatization enhanced lignin solubility in THF and improved chromatographic results. Universal calibration led to about three times higher molar mass values than by conventional calibration.