Wood is an amazing material that breathes and interacts with the water around it. It absorbs water from the air and releases it back, depending on the temperature and humidity. This is both a blessing and a curse – while it helps regulate indoor climates, it can also lead to wood warping or becoming a playground for fungi and insects.
Water in wood comes in two main forms. There’s the free water, which sits in tiny spaces called lumens (about 10 to 50 micrometres wide). Then there’s the bound water, which sticks to the wood’s building blocks: cellulose (makes wood flexible), lignin (gives wood compressive strength), and hemicellulose (holds everything together). This bound water is crucial because it greatly influences the wood’s properties, like its tendency to swell or shrink and its resistance to fungi. The bound water behaves differently to the free water that we know. One major difference is that it cannot freeze.
We explored a technique to make wood better at handling water (e.g., in outdoor conditions) by treating it with a special resin, which is called phenol urea formaldehyde resin. This resin treatment makes the wood more resistant to fungi and improves its swelling and shrinking properties. Our goal was to find out if this improvement was because of a reduction in the bound water content.
To figure this out, we used a method called differential scanning calorimetry (DSC). We froze water-soaked wood samples at -30°C and then carefully thawed them, measuring how much water melted (free water) and how much melted not (bound water). We did this before and after treating the wood with resin, across different wood species.
Our experiments showed that the resin treatment reduced the bound water content in all wood species we tested. Interestingly, some species showed a much bigger reduction than others and we don´t know why yet.
I embarked on this research out of curiosity. In my PhD research, I noticed that different wood species behaved differently after the resin modification, and I wanted to find out why. I believe that if we understand what improves the wood during the modification, we can develop new and better technologies to produce long-lasting wood products. This not only benefits the construction industry but also helps in the sustainable use of natural resources.
Keywords: wood water interaction, DSC, wood modification, Phenol urea formaldehyde (PUF) resin
Authors
Carlo Kupfernagel
Institute of Wood Technology Dresden (IHD), Germany
Morwenna J Spear
BioComposites Centre, Bangor University, United Kingdom
Graham A Ormondroyd
BioComposites Centre, Bangor University, United Kingdom
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