A powerful combination to explain nanoscale wood-water interactions

Cellulosic materials from wood to novel nanomaterials are highly sensitive to moisture. The fundamental mechanisms underlying wood-water interactions remain poorly understood. The unique combination of experimental and computational research carried out in the SASAMIS project provides detailed information on the effects of moisture on the nanoscale building blocks of wood fiber walls.

See also in Nano Letters: https://pubs.acs.org/doi/10.1021/acs.nanolett.2c00822

Wood cell walls interact with moisture in a highly sophisticated way. These interactions are dominated by nanoscale phenomena, and they are thus inherent to most cellulosic materials. The softening of wet paper is a familiar example of the dramatic effect of moisture on wood-based materials. Despite their great importance for advanced applications of wood, the details of how water interacts with cellulose microfibrils has not been properly described.

Water is one of the major structural components of wood cell walls. Its distribution within the cell wall nanostructure determines many of the material properties, including the accessibility to chemical reagents. Changes in external moisture conditions lead to changes in the water distribution, which eventually affects the structure of cellulose microfibril bundles. How and why exactly water enters the interfibrillar spaces, and how this affects the structure of the fibril bundles are subjects of active research worldwide.

In the FinnCERES-funded project SASAMIS, we have built a realistic model of microfibril bundles in spruce wood. The model’s molecular architecture and behavior with moisture changes correspond well to experimental results. It can be used to explain the mechanisms behind wood-water interactions, to predict water mobility and structural changes with moisture, and to support the interpretation of experimental results.

The new information obtained in SASAMIS leads to a deeper understanding of the fundamental properties of wood-based materials. This can serve as a starting point for the development of new kinds of cellulosic materials that exploit the special interaction with water.

Unique combination of methods

SASAMIS uses a unique combination of methods to probe the molecular-level effects of water on the microfibril bundles. Studying the nanostructure of wood under varying external conditions, such as different moisture contents, is difficult. X-ray scattering offers a possibility for non-invasive characterization in the nanometer scale, but the interpretation of the results is often challenging. Molecular modeling allows us to see more clearly the relation between real structures and the scattering data, and additionally enables the prediction of structural changes.

The enabling role of FinnCERES

In SASAMIS, researchers at Aalto University combine their expertise in X-ray and neutron scattering with the molecular modeling expertise of VTT. The fruitful collaboration of the principal investigators Paavo Penttilä at Aalto University and Antti Paajanen at VTT was enabled by the FinnCERES Novel Openings funding.

New adaptable methods for modeling and characterization

The toolkit developed in SASAMIS is versatile and can be adapted to various other research topics. The powerful combination of modeling and scattering is foreseen to provide answers to research questions dealing with cellulose dissolution and drying behavior.

Read more about the work from the recent article Nanoscale Mechanism of Moisture-Induced Swelling in Wood Microfibril Bundles published in Nano Letters.

Additional information:

Paavo Penttilä

Academy Research Fellow

Aalto University

Antti Paajanen

Senior Scientist

VTT Technical Research Centre of Finland