Wood stores CO2, which makes it a valuable material for reducing climate change. In essence, CO2 can be sequestered to a greater extent when more wood is used. Wood used for exterior structures like windmills and bridges needs to be resistant to insects and fungi. However, many local species are classified as not durable. They would already decay within a few years. One way to get this durability is by wood modification. While there are various approaches possible, all are usually non-biocidal and change the structure of the wood at the cell wall to lower the moisture content. Certain wood species—sapwood, in particular—absorb chemicals more easily than others. Since of this, veneers are especially appealing for wood modification since, in comparison to thicker solid wood, their thinness allows an easy and more uniform uptake of chemicals.
In this study, we manufactured laminated veneer lumber (LVL), and exposed it in-ground contact at a test field in Stamsmåla, Sweden for a number of years in accordance with the EN 252 (2015) standard. Pre-treatment was applied to the veneers using a variety of phenol resins with varying molecular sizes. Thereby was the molecule size critical, since it is known that the resins needs to penetrate the cell wall, to achieve a long-term improvement in durability. So-called low-molecular size resins, able to penetrate the cell-wall, were used. They were applied at a range of 0 to 60% for the weight percent gain (WPG) and 2 to 6 N/mm² for the pressure at which the LVL was manufactured. On the same test field, we also exposed acetylated LVL (WPG of around 24%). The veneers were acetylated on an industrial scale at a test side of Accsys Technologies and bonded to LVL at the laboratory at the Georg-August University Goettingen.
The results indicated that untreated references decayed within four years of in-ground contact. In contrast, resin-treated samples showed significant improvement in decay resistance, even after nine years of exposure, although the effectiveness depended on the resin loading. The applied pressure seemed to have a minor impact on the decay resistance. The acetylated LVL showed no signs of decay, consistent with known improvements of acetylated wood. However, the acetylated specimens have only been exposed since 2022.
In the upcoming years, the test field specimens will be further evaluated.
Keywords: Acetylation, laminated veneer lumber (LVL), durability
Authors
Maik Slabohm
Wood Biology and Wood Products Department, University of Goettingen, Germany
Holger Militz
Wood Biology and Wood Products Department, University of Goettingen, Germany
Login to download the PDF