Public defence, Bioproduct Technology, MSc (Tech) Saija Rantanen

Title of the thesis: Cellulose reactivity: Assessment and applications

Thesis defender: Saija Rantanen 
Opponent: Prof. Monica Ek, KTH Royal Institute of Technology, Sweden.
Custos: Prof. Tapani Vuorinen, Aalto University School of Chemical Engineering

More products are being manufactured today than ever before. At the same time, the amount of waste generated and the impacts of using the limited global fossil resources raise concern. There is a clear need for resource-efficient processes that rely on sustainable feedstocks and minimize waste generation. Cellulose offers a renewable, recyclable, biocompatible, non-toxic and abundant alternative to fossil-based raw materials. However, manufacturing value-added products of cellulose usually requires its chemical or enzymatic modification or dissolution. Hence, its efficient use requires improved understanding of cellulose accessibility and reactivity, and due to its recalcitrant nature, a pretreatment is often needed to increase the accessibility and reactivity.

This thesis investigates how cellulose structure and pretreatments affect its accessibility, reactivity, and dissolution. First, a method based on dynamic vapour sorption (DVS) with deuterium exchange was developed to assess cellulose accessibility quantitatively. Cellulose accessibility was found to correlate with cellulose crystallinity and pulp porosity, hemicellulose content, and processing history.

Second, this thesis investigates cellulose dissolution in the aqueous NaOH/ZnO solvent system. Dissolution was found to markedly increase cellulose reactivity, indicating molecular-level accessibility of reactive sites. In addition, it was demonstrated that cellulose dissolved in aqueous NaOH/ZnO no longer exhibits crystalline order, although the cellulose chains remain structurally confined. Based on these findings, formation of a metastable cellulose–zinc complex was proposed, providing new insight into the role of ZnO in cellulose dissolution.

Third, the effect of hydrothermal pretreatments on pulp reactivity and dissolution in aqueous NaOH/ZnO is examined. Medium-consistency treatments (10% dry matter) improved dissolution, while high-consistency treatments (50% dry matter) with more severe conditions led to fibre hornification and poorer dissolution. The intrinsic viscosity had a strong influence on pulp dissolution. The fibres began to dissolve when the degree of polymerisation fell below approximately 550, suggesting that cellulose chains must be sufficiently short to disentangle from the fibril structure to be able to dissolve.

Overall, the findings of this thesis provide new insights to how cellulose structure and pretreatments affect cellulose accessibility, reactivity, and dissolution, supporting more efficient use of cellulose as a sustainable raw material.

Keywords: Accessibility, cellulose, pulp dissolution, pulp pretreatment, reactivity

Thesis available for public display 7 days prior to the defence at Aalto University's public display page.

Contact information: 
saija.rantanen@aalto.fi 
https://www.linkedin.com/in/saija-rantanen-34998196/