Water behavior, equilibrium, and migration of a biomaterial made of pure mycelium

Mycelium materials are an emerging class of natural, inexpensive, and environmentally sustainable materials. They are promising alternatives to petroleum-based polymeric ones, and they can also be used as substitutes for animal-based leather. This work investigates the water relation properties (equilibrium and transfer) of pure mycelium materials produced using Ganoderma lucidum fungal species in liquid-state fermentation. The dynamic gravimetric method was used to determine sorption isotherms at four temperatures (20 °C, 30 °C, 40 °C, and 50 °C) over a water activity ( a w ) range of 0 to 0.9. This material is highly hygroscopic and depicts a huge condensation phase at high water activity, with an equilibrium moisture content of 53% at 20 °C and 90% RH. Among the eight sorption models tested, the GAB model gives good results and was further used to analyze data. Thermodynamic properties (net isosteric heat of sorption, sorption entropy change, and the isokinetic temperature) were determined from the sorption isotherms to represent better the energy related to the sorption processes. Finally, the transient stages of sorption measurement were analyzed to extract mass transfer properties. Consistently with the morphology of this material, a dual-scale effect is evidenced, which turns into a representation by two independent parameters: the macroscopic and microscopic mass diffusivity values.