In this thesis we explore several strategies for the valorization of forestry residues, which account for 30% of lignocellulosic biomass from forestry operations and are currently incinerated, due to the lack of feasible methods of fractionation of the complex feedstock. To address this challenge, chemical conversion methods capable of processing different components have been developed.

In the first chapter, valorization of spruce wood from tops and branches (T&B) was investigated. A fast fractionation method was applied to obtain three main fractions from spruce T&B: solid residue, organic, and aqueous fractions. The solid residue, comprised mainly cellulose, lignin, and small amounts of hemicellulose was converted to textile fibers. The organic fraction, rich in lignin, was converted into hydrocarbons. The environmental sustainability of the process was studied by life-cycle assessment (LCA) and demonstrated better scores in four out of five footprint categories benchmarked to cotton production. 

In the second chapter, conversion of spruce bark into different high-value compounds, such as starch, lipophilic extractives, lignin, tannins, and cellulosic pulp is presented. Pulping under alkaline conditions was chosen as a methodology to delignify bark and obtain cellulosic pulp. To enhance the efficiency of extractions and soda pulping process, a flow-through system was used. The flow-through system demonstrated tunability in the pulping step to achieve either high yields of lignin or pulp depending on the applied temperature. The process also allowed for the mechanical separation of condensed tannins from the cellulosic pulp. LCA showed that conversion of bark into valuable products is more climate-beneficial than combustion.

In the third chapter, the possibility of fractionating a mixture consisting of birch bark and wood, that represents T&B was demonstrated. Two different catalytic approaches allowed us to sequentially isolate monophenols, suberin and yield a cellulose-rich pulp, showing that valorization of complex mixtures could offer a more resource-efficient alternative to incineration. 

Overall, chemical conversion approaches for efficient fractionation of barks and T&B to a variety of compounds that can substitute fossil-based products on the market, was investigated in this thesis.