Mycelium as a Sustainable, Low-Carbon Material for Building Panels

Filamentous eukaryotic fungi are ubiquitous in soil habitats. Long filaments, called hyphae, of diameter 1–30 μm form a network called mycelium. The mycelium grows into and breaks down surrounding organisms to provide nutrition for the fungus. Techniques have been developed that introduce fungal spores into a cellulosic matrix, permit the mycelium to grow and bind together the particles of the matrix, resulting in a mycelium-based composite (MBC). The growth is stopped by effectively “killing” the fungus, usually by heating to 80 °C or above. Some of the key advantages of MBCs compared to conventional materials include their low-embodied carbon footprint, the potential to valorize waste agricultural and wood materials, the ability to manufacture these bio-composites locally, and the potential to bio-degrade the bio-composites at the end of life (i.e. they can be composted). Most mycelium composites to date have been used for insulation or packing material applications. More recently, an MBC that incorporates a cotton textile, hemp particles (hurd) and mycelium binder has been developed and is purported to have improved mechanical properties. This paper presents nine cylinder compression tests and one beam bending test. This mycelium composite has an average compressive strength of 0.7 MPa (based on a 0.2% off-set value) and average compressive secant modulus E = 37 MPa. On the other hand, it is relatively low density (average 285 kg/m³). The stress–strain response is highly non-linear, even at strains below a 0.2% off-set yield stress. It exhibits hysteretic behaviour, and repeated load cycles lead to permanent strain. The composite has a higher initial stiffness in bending (2.7 times greater), but a lower yield moment (58% less), than would be expected based on the compressive stress–strain response. This may be due to differences in the load sharing between the textile, hurd, and mycelium under different loading regimes.