Lignin modification and degradation for advanced composites and chemicals

Abstract

Over centuries, our society mostly relies on fossil fuels for majority of commodity materials, chemicals, plastics as well as energy sources derived from petroleum, coal and natural gas. The overutilization of fossil fuels to fulfill the inflation will cause the inevitable issues including dwindling of available resources and global environmental problems. With the awareness of the severe consequences of the society’s over-dependence on fossil fuels, identifying sustainable and renewable alternatives has attracted significant and increasing attentions. Lignocellulosic biomass is one of the most accessible renewable forms of carbon and has been regarded as one the most logical feedstock to replace traditional fossil resources. It is suggested recently that coupling of “biomass-conversion technologies” with “land-use” could meet the nation’s increasing need for fuel without affecting food, feed and fiber production. However, most of the current biorefinery products are from the first-generation cellulosic projects, where most lignin is burnt for heating directly similar as the traditional pulp and paper industrial. Consequently, the advent of biorefineries that convert cellulose into liquid fuels generate more lignin than necessary substantially, which is a major waste of natural resources. Therefore, lignin valorization into value-added products is worthy to bio-refinery concept in particular and in general to the society. With this purpose, my doctoral thesis focuses on modification and degradation of lignin for advanced chemicals and composites. In the first part of my research, a study on synthesis of lignin-based surfactant via chemical modification is explored. The modified lignin shows great potential as a surfactant which decreases the interfacial tension between styrene and water dramatically. Besides, this lignin-based surfactant is further demonstrated to be effective to prepared stable water-in-oil emulsions. In the second part, an effective route to prepare lignin/polystyrene composites foam through high internal phase emulsion (HIPE) polymerization is disclosed. Lignin is demonstrated to be good fillers and substitution of traditional polymer through the investigation of its effects on the properties of the composites. The third part describes a new catalytic system which can degrade lignin into aromatic compounds under very mild conditions. Furthermore, in the fourth part, this catalyst system was used in biomass pretreatment, where wood chips were pretreated directly without grinding. It is demonstrated that the addition of NaNO3 into FeCl3 and O2 serves as a bridge between oxygen (gaseous phase) and iron salts (liquid phase) to improve the re-oxidation rate of Fe2+ and thus promote the overall degradation rate. In summary, the lignin valorization through modification and degradation into composites and chemicals is explored in my research.