The relationship between water and wood is at the heart of wood materials research. The topic has fascinated scientists for centuries. However, there are still issues related to these two elements crucial to mankind that remain to be discovered.
Wood has evolved to operate in an environment where it's immersed in water because trees are immersed in water and the whole purpose of wood is is is a structural support for the canopy of the tree and it's to transport water and nutrients up to the canopy and the products of photosynthesis down from the canopy into the roots. So, it's it's it's designed, if you like, if you want to use that word, to operate in a very water-rich environment. The water in wood is linked to all its properties.
A better understanding of this will enable researchers to manage the features and contribute to extending the lifespan of wooden products. The worst enemy for wood is always water. So, that's why our group is concentrating on wood and water interactions.
We need to study how water molecules are entering in wood, in which locations they are entering in the wood. Is it in in late wood, early wood, or cell wall level? What we know is that wood keeps exchanging water with its surroundings.
So, we need to understand quite at the fundamental level how wood and water are interacting. We can also have situations, for instance, where wood will be in contact with concrete or wood will be under load. And how how then these wood and water are interacting and what can we do then to to bring a solution?
In an Academy of Finland funded research project, Waterwood, Professor Lauri Rautkari and his team are studying the water vapor sorption behavior of wood under load. It's important that we start to understand that the when there's a high tension or high compression in wood, something like in in high-rise buildings, there's always some some tension and compression in different places. So, I we did some pretests and we found out that there are certain differences in moisture, maybe 2-3% of moisture, and that can lead some micro cracks in in wood.
So, if you stretch wood or if you press wood, it will interact in a different way with water and this is what we want to be able to show and then to understand and to bring a solution. Preliminary results indicate a clear difference. Stretching wood creates a tension, which inhibits water molecule uptake, while compressing wood creates more area for water absorption.
The group is developing new methods to analyze moisture content, which can be applied to any hydroscopic material that absorbs humidity from the air. Tainesi Loring Song is using an M cell device to control the humidity in infrared spectroscopy. We have combined this humid generator and we have a chamber where we put wood in there and we can set specific relative humidities and then we can see, for instance, how wood was interacting with water under a load and we can understand how the the the chemical structure of wood is looking like.
A very central concept in wood material science is equilibrium moisture content, which means that wood always interacts with the surrounding moisture to create balance. When the water is absorbed into the wood, it creates an internal pressure, which makes the wood expand. And this, if we maintain the relative humidity of the atmosphere at a certain level, we will get a moisture content that stabilizes and that's called an equilibrium moisture content.
I think the view that what's causing that is the internal pressure that the water molecules are applying to the cell and then there's a restraint on that. Part of it is to do with the structure, the kind of winding of the cellulose microfibrils in the cell and and what's outside that in what's called the middle lamella, but also the lignin acts as a restraint on that expansion. So, there's this kind of fight going on, if you like, between tension that's being created in the the bonds of the lignin molecule and the lignin molecules and the hemicelluloses, not so much the cellulose, and the pressure this water is applying.
And that, we think, controls this moisture content. There are several methods used by the researchers to study wood-water interactions and follow changes on the cellular level. The most prominent method that we're using is dynamic vapor sorption.
This is the kind of go-to method where we start, where it's basically very sensitive balance, but depending on the research question, there's a lot of different methods that we're applying. If we, for instance, want to know where you want to locate the water, where is it in the wood, we can use different chemical imaging methods. If you want to know not just the amount, the mass of water in the wood, but also how is it associated with absorption sites, where does it bind to, we can we can have a method called atomic exchange.
Although many of these methods have existed quite a while, combining them and adding computational methods to the equation is providing researchers with new kinds of information, even on a cellular level. It can be quite beneficial to apply different chemical imaging techniques, combining large field of view, low resolution, like the NIR hyperspectral camera, with a technique of high spatial resolution, but small field of view. So, we're combining both methods and we're using both benefits, having a nice overview over the microscopic distribution of chemical variation, but also having the detailed information on a cellular level.
By deepening our understanding of the properties of wood, we develop new wood treatments, improve the overall sustainability of wooden products, and reduce our dependence on fossil-based raw materials.
