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Division of Forest and Forest Resources

Increased valorisation of domestic timber by a novel wood modification system

Finished Last updated: 31.12.2022
End: dec 2022
Start: jan 2020

Sustainable forestry providing timber, solves societal challenges with green chemistry, giving economical growth through durable wood products

Status Concluded
Start - end date 21.01.2020 - 31.12.2022
Project manager Andreas Treu
Division Division of Forest and Forest Resources
Department Wood Technology
Funding source The Norwegian Research Council

Wood modification provides dimensional stability and extends the service life of wood by minimising threats from biological attack. Modified wood has gained market share in Europe across a range of Use Classes. A novel wood modification system using a combination of sorbitol and citric acid in wood has shown enhanced properties such as increased dimensional stability, increased durability against decay fungi and less susceptibility to blue-stain fungi. Many domestic timber species are not used for wood modification because of their refractory behaviour, inhomogeneity or small and variable dimensions. However, fast growing spruce and underutilized birch, as well as Scots pine are all candidates for wood modification. In addition, reducing the wood dimensions, for example cutting veneer, would make it easier to treat and modify the material. Utilizing glueing and self-laminating properties of such modified veneer for engineered wood products would broaden the application portfolio.

The main objective of ValorWood is to further develop a novel wood modification system from bench scale to pilot scale and to provide new use areas for Norwegian wood species. Treatment and process will be optimized, material properties will be evaluated, the environmental impact and the economic feasibility will be analysed.

Publications in the project


There is a need for new solutions in wood protection against marine wood borers and termites in Europe. A new solution could be the esterification of wood with sorbitol and citric acid (SCA) since these are inexpensive and readily available feedstock chemicals and have shown protective properties against fungal wood degradation in earlier studies and prevented macrobiological degradation, as shown in this study. Protection of wood products in the marine environment lacks available wood preservatives that are approved for marine applications. Termite infestation is opposed mainly by biocide treatments of wood. Several wood modification systems show high resistance against both marine borers and subterranean termites. However, the existing commercialized wood modification products are costly. Both macrobiological forms of degradation represent a great threat for most European wood species, which are rapidly and severely degraded if not properly treated. This study investigated esterified wood in standard field trials against marine wood borers, and against subterranean termites in laboratory trials in a no-choice and choice test. The treatment showed good resistance against wood borers in the marine environment after one season and against subterranean termites in the laboratory after eight weeks. The low termite survival rate (SR) in the no-choice test during the first week of testing indicates a mode of action that is incomparable to other wood modification treatments.

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The aim of this research is to determine if the polyesterification of sorbitol and citric acid in wood has a future potential as a wood modification process. Pine wood was impregnated with an aqueous solution containing citric acid and sorbitol and was thereafter cured at 103 or 140°C for 18 hours. The dimensional stability and leaching resistance were studied for both modification temperatures. The leachates from the modified wood samples were analysed by HPLC and the susceptibility to decay and staining fungi were studied. Impregnated samples cured at 140°C showed a permanent (leach-resistant) increased dimensional change, but samples treated at 103°C were not stable to leaching. Treated samples cured at 103 and 140°C showed significant resistance to white-rot (Trametes versicolor) and brown-rot decay (Postia placenta) after a leaching procedure. Furthermore, samples cured at 103 and 140°C (leached and unleached) were significantly less susceptible to blue-stain fungi than the untreated controls.