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.

If valorization of tops and branches would be realized, there is potential to increase the overall yield from forestry by 50%, which would impact land use change and climate change considerably. Currently, these residues are either incinerated or left to decay in the forests. The main challenge of valorization of tops and branches is their composition: comprising both wood and bark that are mechanically inseparable. Herein, we propose a chemical approach to valorize all components of both wood and bark of tops and branches without prior mechanical separation. By applying a sequential fractionation sequence involving two different catalytic steps, all different parts of the tops and branches have been valorized into well-defined streams and an intact cellulose-rich pulp. It was found that the sequence of processes was important for the overall outcome. We hope that this first report of the valorization of tops and branches will inspire further studies to unlock the full potential of this challenging yet abundant feedstock.

In this study, cellulose-based films were developed by using microfibrillated cellulose (MFC) and lignin-containing microfibrillated cellulose (Lig-MFC) derived from sequentially extracted spruce bark. The films were coated with the hydrophilic extractives from the fractionation, resulting in additional MFC-coated and Lig-MFC-coated cellulose films. A combination of morphological (AFM), surface (water contact angle (WCA), roughness), optical (UV–vis), and mechanical properties was analyzed to assess structure–property relationships. Coated films exhibited significantly enhanced hydrophobicity and UV-shielding, with WCA increasing from 47° to 76° for MFC and from 66° to 71° for Lig-MFC. Notably, MFC-coated films displayed superior mechanical performance, with a tensile strength of 119 MPa and elongation of 11%, surpassing most lignocellulosic-based films in the literature derived from bark. In addition, this tensile strength falls within or above the range of commonly used materials, such as kraft liner, PET, and LDPE, suggesting realistic opportunities for substitution in short-lived packaging applications. AFM analysis revealed a reduction in surface roughness after coating, correlating with an enhanced WCA. Compared with similar biobased films in the literature, the extractive-coated MFC films show superior performance in terms of strength, flexibility, and UV-shielding properties. This valorization route offers both economic and environmental sustainability advantages compared with incineration for energy recovery. A comparative life cycle assessment (LCA) study showed that valorization of the pulp and hydrophilic extractives from the bark biorefinery into different qualities of MFCs gave substantial climate change benefits stemming from the possibility of substituting packaging materials with high inherent environmental impact.

Bark represents 10 % dry weight of spruce trees and is a major side stream from pulp production. Currently, pulp mills burn bark to produce energy with a low economic value, directly emitting biogenic carbon dioxide to the atmosphere. Biorefining bark using a continuous flow-through fractionation process generates high added-value compounds (tall oil, starch, phenol, and pulp) that allow for extended carbon storage durations. This study assesses the potential future environmental impacts of valorising bark instead of burning it. We conduct a LCA study combining a prospective consequential modelling perspective with an input-related functional unit and account for the effects of storing biogenic carbon in the bark-based products. Our findings show that biorefining bark maintains lower environmental impacts than combustion, reducing time-differentiated climate impacts by up to 30 %, but only when the carbon dioxide used for pulping is recirculated and the fractionation processes are integrated with a co-located pulp mill supplying surplus waste energy, considered to have no associated environmental impacts. Storing biogenic carbon for a longer period of time has a positive effect on mitigating short-term climate impacts. However, our analysis reveals that while time-dependent climate impacts decrease, there is an increase in human toxicity and ecotoxicity impacts, with combustion performing better in these categories. This highlights the importance of expanding the scope of LCA studies to include impacts beyond climate change. Overall, this work demonstrates that combining a prospective consequential modelling perspective with an input-related functional unit is a relevant approach to study potential future impacts of emerging biorefineries and thus supports the development of a sustainable circular bioeconomy.

This study presents a sequential fractionation of spruce bark employing a flow-through system that enables continuous extraction without the need to change the chamber during the process. Various bark components such as lipophilic extractives, noncellulosic sugars, and lignin were extracted under mild conditions and within short timeframes compared to the batch process. The utilization of the flow-through system enabled efficient extraction without degradation of products that were observed during the batch process. By recirculating the solvents containing extracted components, the solvent/biomass ratio could be reduced considerably, without degradation of the products. The results demonstrate an energy efficient approach to obtaining valuable components from spruce bark, paving the way for a future biorefinery.

To make biorefining more environmentally sustainable, preferably residues from forestry should be used and more than one fraction should be upgraded. A third of raw materials from forestry & horbar;tops and branches (T & B)― are either left in the forests or collected and incinerated to a low value. Herein, we apply a fast fractionation to valorize two of the fractions of this forestry residue. The cellulose is converted to textile fibers and all the lignin to hydrocarbons. The environmental sustainability of the novel value chain was studied by life cycle assessment (LCA), and benefits were found in four out of five impact categories. These are important steps to increase fiber production without affecting environmental impact, making biorefining competitive.

If valorization of tops and branches would be realized, there is a potential to increase the overall yield from forestry by 50%, which would impact land use change and climate change considerably. Currently, these residues are either incinerated or left to decay in the forests. The main challenge of valorization of tops and branches is the composition: comprising both wood and bark that are mechanically inseparable. Herein, we propose a chemical approach to valorize all components of both wood and bark of tops and branches without prior mechanical separation. By applying a sequential fractionation sequence involving two different catalytic steps, all different parts of the tops and branches have been valorized into well-defined streams and an intact cellulose-rich pulp. It was found that the sequence of proceses was important for the overall outcome. We hope that this first report of the valorization of tops and branches will inspire further studies to unlock the full potential of this challenging yet abundant feedstock.