Exploring the use of X-ray micro CT as a tool for the monitoring of moisture production and mass loss during lab-based fungal degradation testing

IRG/WP 19-20654

L De Ligne, J Van den Bulcke, A De Muynck, J M Baetens, B De Baets, L Van Hoorebeke, J Van Acker

Bio-based building materials, such as wood and wood-engineered products, are susceptible to degradation by decay fungi. In-depth knowledge on the intricate material-fungus relationship as well as performance data for many bio-based building materials are still lacking, and especially knowledge on how a material’s structure and moisture properties affect the degradation process is missing. Although durability data is available for solid wood, the standard tests, mainly measuring the mass loss caused by decay fungi after sixteen weeks, do not offer much information on what is going on inside the wood during degradation. Notwithstanding that standard tests are excellent for testing the durability of a certain wood species or the efficacy of a preservation product, we need to gain more insight, and there, X-ray CT comes into play. As this non-invasive technique allows to assess the density of wood in three dimensions, it enables us to obtain localized info inside wood during degradation, without disrupting it. In this paper, we will describe the challenges associated with X-ray CT scanning for monitoring of fungal degradation during lab testing. First, dose tests were performed to assess the recovery potential of brown-rot fungus Coniophora puteana after exposure to X-radiation. Then, a set-up was designed allowing for a stack of Petri dishes to be scanned automatically one after the other, avoiding unnecessary exposure of the fungal cultures not in the field of view. A first substantial test was performed on mini-blocks of Scots pine sapwood under degradation by C. puteana, scanned at weekly intervals with X-ray micro CT. The resulting data show the weekly variation in density for each wood block but are not straightforward to interpret. Several factors affect the results: we assessed that moisture uptake from the agar medium and moisture production by the fungus increase the average density profile, while water evaporation and mass loss due to degradation decrease it. The main challenge seems to be to untangle these factors. We therefore additionally analysed the density of mini-blocks subjected to the same set-up but without fungus, to quantify the impact of moisture uptake from the agar and water evaporation on the density over time. Density variations over time (0.02-0.08 g/cm³) were observed for the mini-blocks under degradation. We hypothesize that density increases are caused by fungal moisture production as a result of increased metabolic activity. Additionally, we establish a link between the occurring density pattern and the degradation of the different nutrient sources in Scots pine wood by C. puteana described in literature. In the future, more experiments will be performed to further investigate these hypotheses, and the technique will be applied to other bio-based materials as well.

Keywords: adation process, moisture production, X-ray CT, Coniophora puteana

Conference: 19-05-12/16 Quebec City, Canada

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