Material characterization of pressed and unpressed wood–mycelium composites derived from two Trametes species

Mycelium composites have received increasing interest lately as biodegradable materials with promising properties making them potential substitutes for different fossil-based plastics, especially expanded polystyrene (EPS). However, only a small fraction of the various combinations of fungi and lignocellulosic waste have been described so far, mainly focusing on agricultural substrates and a handful of fungi. It is thus important to investigate and compare the properties of different mycelium composites and influences of post-processing options. In this study, composites were produced utilizing two related white rot fungi, namely Trametes versicolor and Trametes pubescens, and beech wood sawdust, where part of the composites were hot pressed. Mechanical properties of the composite materials were comparable or even superior to those of EPS. T. pubescens covered the substrate with a thicker, but more foam-like mycelium than T. versicolor, exhibiting a higher tensile strength and fracture strain, but also higher flammability. Water uptake of mycelium composites at elevated relative humidity could be reduced by hot pressing. Studying the dependency of material properties after hot pressing revealed clear differences, such as decreased hydrophobicity in terms of water contact angle and merging of aerial hyphae for T. versicolor but not T. pubescens visualized with scanning electron microscopy. Additionally, the work of fracture increased for specimens of T. versicolor but decreased for those of T. pubescens after hot pressing. This study indicates that fungal species selection can be an important factor when hot pressing of mycelium composites is considered.