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.
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 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.