Aleksi Zitting: Investigating moisture behavior of wood nanostructure using experimental and simulated scattering

Content of the thesis: 

Wood is a common material used in various practical applications and as a raw material for many bio-based materials. Despite the complex and hierarchical structure of wood, the bulk of its structure consists of thick cell walls. These cell walls, in turn, are mainly made of cellulose, hemicellulose, and lignin which are nanometer-scale biomolecules. As wood is former living tissue, water interactions are important for the material properties of wood. Investigating the fundamental cause of the moisture-related behavior of wood, which arises inside the cell walls, is difficult while keeping the cells intact and in ambient conditions.

In this thesis, the nanoscale moisture behavior of the wood cell wall is investigated by combining experimental X-ray and neutron scattering with atomistic simulations of the cell wall biomolecules. Scattering experiments allow us to investigate how the wood nanostructure changes at various moisture conditions while molecular dynamics simulations aid in understanding how the cell wall constituents interact with each other and water.

In this work, we show that the moisture content-related drying behavior is linked to the deswelling of cellulose microfibrils in the cell wall. Both the experimental and modeling results indicated that microfibril aggregation is a significant contributor to nanostructural changes at lower moisture contents. The moisture-related behavior of delignified wood was similar to untreated wood, indicating that lignin is a closer to a passive, rather than an active participant in wood-moisture interactions. Simulation results suggest that hemicellulose may appear as an apparent increase in microfibril size seen with scattering.

The results of this thesis advance the fundamental understanding of wood nanostructure which should aid both in the practical use of wood and in the production of advanced bio-based materials in the future

Opponent: Doctor Nayomi Plaza, USDA Forest Products Laboratory, USA

Supervisor: Professor Lauri Rautkari, Aalto University School of Chemical Engineering 

Link to electronic thesis: LINK

Link to the remote defence: LINK