Wood-Decaying Fungi: From Timber Degradation to Sustainable Insulating Biomaterials Production

Abstract

Addressing the impacts of climate change and global warming has become an urgent priority for the planet's well-being. In recent decades the great potential of fungal-based products with characteristics equal to, or even outperforming, classic petroleum-derived products has been acknowledged. These new materials present the added advantage of having a reduced carbon footprint, less environmental impact and contributing to the shift away from a fossil-based economy. This study focused on the production of insulation panels using fungal mycelium and lignocellulosic materials as substrates. The process was optimized, starting with the selection of Trametes versicolor, Pleurotus ostreatus, P. eryngii, Ganoderma carnosum and Fomitopsis pinicola isolates, followed by the evaluation of three grain spawn substrates (millet, wheat and a 1:1 mix of millet and wheat grains) for mycelium propagation, and finishing with the production of various mycelium-based composites using five wood by-products and waste materials (pine sawdust, oak shavings, tree of heaven wood chips, wheat straw and shredded beech wood). The obtained biomaterials were characterized for internal structure by X-ray micro-CT, thermal transmittance using a thermoflowmeter and moisture absorption. The results showed that using a wheat and millet 1:1 (w/w) mix is the best option for spawn production regardless of the fungal isolate. In addition, the performance of the final composites was influenced both by the fungal isolate and the substrate used, with the latter having a stronger effect on the measured properties. The study shows that the most promising sustainable insulating biomaterial was created using T. versicolor grown on wheat straw.

Keywords: Fomitopsis pinicola; Ganoderma carnosum; Pleurotus eryngii; Pleurotus ostreatus; Trametes versicolor; biomaterials; fungal mycelium; lignocellulosic feedstock; material bio-fabrication; mycelium-based composites; sustainable insulation; wood by-product valorization.

Figure 1

Two-way ANOVA Tukey’s range test for mycelium growth speed at different (a) temperatures and (b) culture media with a 95% confidence interval.

Figure 2

G. carnosum, T. versicolor, P. ostreatus, F. pinicola and P. eryngii growth on different media after 7 days of incubation at 25 °C.

Figure 3

Radial mycelial growth on PDA petri dishes at 25 °C for G. carnosum (GC), T. versicolor (TV), P. ostreatus (PO), F. pinicola (FP) and P. eryngii (PE). Data points represent the mean and the shaded area represents two standard deviations from the mean.

Figure 4

Two-way ANOVA Tukey’s range test for mycelium growth speed in different grain spawn media with a 95% confidence interval. The red dotted line means the 0.00 point.

Figure 5

Mycelial growth trend at 25 °C on a 50% w/w millet and 50% w/w wheat grain mix for G. carnosum (GC), T. versicolor (TV) and P. ostreatus (PO) over time. Data points represent the mean and the shaded area represents two standard deviations from the mean.

Figure 6

Substrates evaluated for biomaterials production: (a) shredded beech wood, (b) oak shavings, (c) tree of heaven chips, (d) wheat straw and (e) pine sawdust.

Figure 7

Radiographies of T. versicolor composites using different substrates.

Figure 8

Example of 3D reconstruction of specimens imaged by X-ray micro-CT of the three different substrates inoculated with Trametes versicolor. AT = Tree of heaven wood chips, WT = Wheat straw, ST = Pine sawdust. For each of the three specimens, at the top left is the solid phase, at the top right is a map of the pores classified by size with a color scale and both are shown at the bottom.

Figure 9

Some global structural parameters of biomaterial specimens (total porosity, mean pore size, specimen specific surface and solid-phase mean thickness). GC = Ganoderma carnosum, PO = Pleurotus ostreatus, TV = Trametes versicolor. AT = tree of heaven wood chips, WT = wheat straw, ST = pine sawdust.

Figure 10

Specimen internal size distributions (left) of the solid phase thickness and (right) of the porosity of tree of heaven wood chips, wheat straw and pine sawdust substrates.

Figure 11

Density and thermal conductivity of mycelium composites produced using various substrates and fungal isolates. The legend regarding the used symbols is on the right of the figure.