Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
Lignin is an aromatic macromolecule present in wood and also a by-product in the process of making paper. For a long time, this by-product has been of no interest except for combustion in the recovery boilers for production of energy. Nowadays, however, there is a great interest of finding an alternative use of lignin, not the least the type obtained from the paper industry black liquor with the process called LignoBoost. Although there is some interesting research concerning the salvaging of lignin, for example as a source for new materials, the chemical constitution and properties are still not fully investigated.
The purpose of this work was therefore to develop a method for a better determination of the molecular mass distribution (MMD) of both hardwood and softwood kraft lignins from the biorefinery. The method of choice is a combination of size-exclusion-chromatography (SEC), where the lignin is fractionated, followed by an analysis of the fractions on a matrix-assisted laser desorption ionization time-of-flight mass spectroscopy instrument (MALDI-TOF-MS). Furthermore, the chemical composition of high and low molecular fractions of LignoBoost lignin was determined with pyrolysis gas chromatography mass spectrometry (Py-GC/MS).
It was shown that the MMD determination method of lignin used until now is sometimes insufficient. Therefore, two separate calibration methods were developed for softwood and hardwood kraft lignins. Included in the method development was also an investigation of the necessity of acetylation when analyzing lignin on SEC using tetrahydrofuran (THF) as the mobile phase. It was found that for softwood lignin from the LignoBoost process, this procedure is necessary while the corresponding hardwood lignin does not require an acetylation.
The chemical composition, determined with Py-GC/MS, of hardwood and softwood lignin did not present any significant differences between the structures of high and low molecular lignin. However, differences were found concerning extractives content in lignin preparations from softwood.
This thesis was performed at Innventia AB.
2010. , 41 p.