Thermal Degradation and Fire Properties of Fungal Mycelium and Mycelium - Biomass Composite Materials

Abstract

Mycelium and mycelium-biomass composites are emerging as new sustainable materials with useful flame-retardant potentials. Here we report a detailed characterisation of the thermal degradation and fire properties of fungal mycelium and mycelium-biomass composites. Measurements and analyses are carried out on key parameters such as decomposition temperatures, residual char, and gases evolved during pyrolysis. Pyrolysis flow combustion calorimetry (PCFC) evaluations reveal that the corresponding combustion propensity of mycelium is significantly lower compared to poly(methyl methacrylate) (PMMA) and polylactic acid (PLA), indicating that they are noticeably less prone to ignition and flaming combustion, and therefore safer to use. The hyphal diameters of mycelium decrease following pyrolysis. Cone calorimetry testing results show that the presence of mycelium has a positive influence on the fire reaction properties of wheat grains. This improvement is attributable to the relatively higher charring tendency of mycelium compared to wheat grain, which reduces the heat release rate (HRR) by acting as a thermal insulator and by limiting the supply of combustible gases to the flame front. The mycelium growth time has been found to yield no significant improvements in the fire properties of mycelium-wheat grain composites.

Waste‐derived low‐cost mycelium composite construction materials with improved fire safety

“…Mycelium exhibited no flame‐retardant properties and functioned purely as a binding matrix phase in the composite. Thermogravimetric analysis of mycelium grown on different substrates showed that the mycelium began to decompose at approximately 250°C (Figure ) with decomposition occurring through a series of reactions that broke the organic constituents down into low molecular weight volatiles . Stable char consisting of primarily amorphous carbon started to form at 500°C (~25 wt%) with a negligible drop in mass at higher temperatures.…”

“…20 wt%) and embedded silica (approx. 20 wt%) during combustion . Char is derived from organic rice hull constituents, especially lignin which is an aromatic compound containing cyclic rings of very stable bonds which do not easily break apart or react with other constituents .…”

“…The formation of char is known to increase flame retardancy by acting as a thermal insulation barrier because of its low thermal conductivity and to reduce smoke because of the ability of char to impede the release of ultrasmall fragments of fibre into the smoke plume . In the presence of oxygen (on air‐exposed surfaces), char will oxidise leaving inert silica behind as the main constituent of the surface residue . Progressive accumulation of these silica layers results in the formation of a silica‐ash layer which acts as a thermal barrier, preventing oxygen flow to the composite core.…”

“…20 wt%) during combustion. 36,42 Char is derived from organic rice hull constituents, especially lignin which is an aromatic compound containing cyclic rings of very stable bonds which do not easily break apart or react with other constituents. 43 These rings decompose into aromatic fragments which are the principal constituents from which char is formed.…”

“…44,45 In the presence of oxygen (on air-exposed surfaces), char will oxidise leaving inert silica behind as the main constituent of the surface residue. 36 Progressive accumulation of these silica layers results in the formation of a silica-ash layer which acts as a thermal barrier, preventing oxygen flow to the composite core. This lack of oxygen flow prevents further oxidation which insulates the virgin materials in a shielding effect similar to fire retardancy improvements noted in organic polymers because of combustion of silicones.…”