Fabrication and Material Characterization of Mycelium Composites Derived from Different Wood-Fungi Combinations

Fungal mycelium is not only digesting biomaterials but can also help in fabricating them by acting as a natural adhesive. A nutrient-rich liquid or solid medium is inoculated with the mycelium to multiply fungal biomass which is then transferred to a grain spawn. Enzymatic digestion of lignocellulosic biomass starts and the mycelium expands in all directions, simultaneously binding the grains together. The same can be observed when the grain spawn has been transferred to the actual substrate after a few days. Using molds in the final growth stage allows to create any desired material shape and once colonization is sufficient, the fungus is killed with heat. As-grown composites do not rely on fossil resources, but lignocellulosic (waste) products and are biodegradable. Adapting and optimizing their properties is possible by using different combinations of substrates and fungi and through treatments such as (hot) pressing. With these three parameters there is already a wide range of materials of which only a few are described so far due to this relatively young approach. Nevertheless, industry is already producing sound insulation panels and packaging from mycelium composites. Material properties of such composites of different fungi on soft- and hardwood sawdust were investigated in this thesis to check the suitability and influence of educts. Further methods that were characterized include hot pressing and the addition of human hair fibers to the substrate. Findings suggest that beech wood chips pose a better substrate for the tested white rot fungi, namely Trametes versicolor, Trametes pubescens and Pleurotus pulmonarius, than spruce. With the mycelium of the brown rot fungus Fomitopsis pinicola too little adhesion for handling of the materials was achieved. The effect of hot pressing was clearly more profound than fungal species and addition of 7 wt.% hair in terms of density, moisture uptake, hydrophobicity and mechanical properties. For a possible application as insulator, the thermal conductivity and flammability of uncompressed composites were evaluated which indicate potential. Morphological observations in different scales revealed effects of heat and compression and imaged colonization.