DFG project launch: HNEE researches the predictability of light-induced colour changes in wood

Studies have already shown that wood changes colour over time. Now, a research team at the Eberswalde University for Sustainable Development (HNEE) and the Thünen Institute of Wood Research in Hamburg-Bergedorf (TI-HF), in collaboration with the Institut für Holztechnologie Dresden gGmbH (IHD), is investigating for the first time whether there is also a connection between time-dependent colour changes and the radiation dose from the sun. The influence of sunlight on the surface could be used to calculate - and therefore predict - the degree of colour change. The three-year project is funded by the German Research Foundation (DFG).

Wood is used as a building material both indoors and outdoors. As a renewable raw material and as a CO2 store when used, its importance is constantly increasing. In addition, wood is subject to various scientific studies, in particular the colour changes of wood have already been extensively investigated. So far, colour changes have always been scientifically evaluated as a function of time. The researchers are interested in whether this is the right measure. "Previously published studies on the light-induced colour change of wood have only evaluated the parameter of time," observes Prof. Dr.-Ing. Alexander Pfriem, project manager and Professor of Chemistry and Physics of Wood and Chemical Process Engineering at HNEE. So far, however, there has been a lack of data on the evaluation as a function of the primary influencing parameter: radiation. "We therefore want to expose various untreated types of wood to natural and artificial sunlight indoors. The irradiation dose (summed surface power density) of the sun is to be measured using a pyranometer behind window glass," adds Claudia Lenz, academic assistant at the Faculty of Wood Engineering at HNEE.

The aim of the project is to develop a new type of analysis that is dependent on both radiation and time. The researchers are also investigating whether there is a calculable correlation between the natural irradiation in the laboratory and the artificial irradiation in the sunlight simulation device. The research team is also investigating the effect of irradiation under the surface of the wood. "The further away the radiation power is from the surface of the wood, the smaller the colour and chemical changes," adds PD Dr habil. Gerald Koch, Scientific Director at the Thünen Institute of Wood Research in Hamburg-Bergedorf. The extent to which the data from this basic research can be transferred to applied research cannot yet be estimated. However, if new findings emerge from the project analyses, these should urgently be taken into account in material tests that are to be developed and tailored to the material wood. The research team hopes that this will establish a new dimension in the evaluation methodology.

About the project

The research project "Predictability of colour changes in interior wood - evaluation as a function of radiation dose as a new approach" (DFG Farbänderungen) deals with the light-induced ageing of wood based on the parameter of radiation dose (summed surface power density) instead of time, as was previously the case. The optical properties of wood vary greatly and depend on the chromophoric functional groups and chromophoric systems present in the wood. In the course of the natural ageing of wood, colour changes occur, which are mainly caused by ultraviolet (UV) and visible (Vis) light radiation and the photo-oxidation induced by this. The aim of this project is to transfer key figures into data-based modelling in order to be able to evaluate the chemical and colour changes of wood based on the radiation dose. This includes analysing the changes via depth profiles.

Sponsor of the project: Deutsche Forschungsgemeinschaft e. V. (DFG)

Duration: 01.03.2021 until 29.02.2024

Funding volume: total: 370,410 euros (303,610 euros plus 66,800 euros programme allowance)

Project consortium:

• HNE Eberswalde, Faculty of Wood Engineering, Department of Chemistry and Physics of Wood with Prof. Dr Alexander Pfriem (Lead) and Claudia Lenz M. Sc
• Thünen Institute, Institute of Wood Research (TI-HF), Hamburg-Bergedorf with PD Dr habil. Gerald Koch as co-responsible
• Institute for Wood Technology Dresden gGmbH (IHD) with Prof. Dr habil. Mario Beyer as co-operation partner