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Dissertation: Chemical and enzymatic oxidation using molecular oxygen as a means to valorize technical lignins for material


Large quantities of lignin are available from chemical pulping and emerging biorefineries. Although using lignin as a fuel will save fossil oil, there is great potential to create higher value for lignin by utilizing it as a source for bio-based chemicals and materials. The main technical lignins, kraft and soda lignins are especially rich in phenolic hydroxyl groups. Molecular oxygen (O2), an environmentally friendly and low-cost oxidizing agent, is active towards phenolic lignin, and is thus a potential choice for lignin valorization. O2 oxidation of lignin can be aided using alkaline conditions or an enzyme as a catalyst.

In Anna Kalliola’s work, a simple alkali-O2 oxidation method was developed to convert wheat straw soda lignin into a polyelectrolyte with increased water solubility. Lignin characteristics could be controlled by the oxidation parameters, especially pH. The oxidized soda lignin solutions were applied as ready-to-use plasticizer product to enhance the workability of fresh concrete. They showed superior plasticizing performance to the commercial lignosulfonate and were comparable to the synthetic superplasticizer when using higher dosing. To enhance the utilization of kraft lignin in composite applications, both laccase- and alkali-catalyzed O2 oxidation were used to polymerize lignin-derived low-molecular phenolics for the reduction of volatile odorous compounds (VOCs). Indeed, the treatment was found to reduce the undesirable odor and the formation of VOCs under elevated temperatures. However, the odor threshold values of the main VOC compounds are extremely low, which poses a challenge to VOC reduction. Kraft lignin functionalization with a hydrophilic phenolic compound was tried in order to lower the glass transition temperature of lignin. Unfortunately, homogeneous polymerization of this compound was favored over coupling to lignin.

The results indicate that alkali-O2 oxidation provides wide possibilities to modify lignin molecular mass and charge properties, which would increase the further application potential of technical lignins.

Public examination 14.8.

The public examination of the doctoral dissertation of DI Anna Kalliola will be held on Friday, 14 August 2015 at noon at Aalto University School of Chemical Technology (Puu2 hall, Tekniikantie 3, Espoo).

Opponent is Assistant Professor Claudia Crestini, Università di Roma Tor Vergata (University of Rome Tor Vergata), Italy. Supervising Professor is Professor Tapani Vuorinen, Aalto University School of Chemical Technology, Department of Forest Products Technology.