A biomimicking approach for hemicellulose processing

University dissertation from Stockholm : KTH Royal Institute of Technology

Abstract: Lignocellulose can become the best opportunity for the society to reduce its dependency on the harmful petroleum based products as well as to produce clean energy. In each part of the production cycle, biomass based products have a better environmental profiles than their petroleum based counterparts. Woody biomass has a vast availability, but it suffers from recalcitrance that is mostly caused by lignin that is functioning as a matrix, surrounding and binding the carbohydrates that are currently the most valuable of the wood components.Lignin-carbohydrate (LC) bonds are believed to be a key element in this recalcitrance and research has shown that these types of bonds are common in wood. These bonds are important in an economical point of view as well, as e.g. residual lignin structures in pulp (lignins bonded to the cellulose and hemicelluloses) require expensive bleaching sequences for their removal.The LC-structures can also be exploited technically as we now have demonstrated. We developed a method that utilizes phenolic end groups that are bonded to different hemicelluloses for cross-linking. The enzyme laccase was used for the cross-linking to create a cost-efficient processing scheme to both isolate and increase the molecular weight of the hemicelluloses. Membrane filtration was used as the key separation technique, which enables the establishment of industrial scale production. The final product had improved mechanical and thermal properties and could be used e.g. as barrier film component in renewable packaging. Nanocomposite formation with nanofibrillated cellulose was also studied. This improved the film properties further. The complexes are also possible to use as model compounds for lignin-carbohydrate complexes in wood.This technique can also be seen to mimick the lignification and lignin-carbohydrate network formation phenomena in plants enabling the formation of entire networks of wood components. Our results suggests that the side chains of hemicellulose might play an important role in network formation and that hemicellulose molecules can carry more than one lignin phenolic end group to fulfill this capability.