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Abstract

In the forest industry, bark is the least utilized biomass resource, with a yearly availability of ~360 million cubic meters. Its low usage is due to its complex structure, chemical composition, and resistance to processing. However, under the right techno-economic conditions, bark has great potential as a source of value-added bioproducts (biochemicals, biofuels, and biomaterials). Thus, this thesis deals with isolating a key building block contained in (birch) bark, contributing to the development of green platforms for the bark-based bioeconomy. The main topics covered the structural characteristics of bark at the cellular scale, the lignocelluloses that form fibers as the scaffold of cell walls, and the extractives within these cells. This document further summarizes our research on the fundamental mechanisms of self-assembly of a birch bark extract, betulin, along with its interfacial behavior and the structure–property correlations that are expected to open new material designs fitting a number of applications. First, the influence of bark layers, pretreatments, and recrystallization times were systematically investigated regarding betulin extraction. This guides furthering betulin-centered material development. Second, the mechanisms involved in the self-assembly of betulin molecules were examined. They included the relationships with molecular packing, solvent-solvate interactions, and supraparticle growth, adding new insights relevant to betulin functionalities. Third, the effects of betulin as a coating component were studied considering the performance of fiber foams that were proposed as a replacement for polyurethane (PU) counterparts. The stability, the compatibility, the durability, and the insulation performance were explored in detail. A life cycle assessment was carried out to confirm the sustainability of the introduced betulin-coated foams. Lastly, to use all the components in bark, the solid residues left after the extraction were considered. A green solvent system was applied to treat the bark fibers and to produce a slurry to generate films tested for their electrical insulation properties in flexible printed circuits. This project revealed how the given treatment conditions affect the dielectric performance of the system and provided guidance for further implementations of biobased dielectrics. Overall, the strategies presented in this thesis demonstrate the potential of bark components to expand value-added chemicals and bioproducts.