Effects of Humidity on Mycelium-Based Leather

Leather is a product that has been used for millennia.
While it
is a natural material, its production raises serious environmental
and ethical concerns. To mitigate those, the engineering of sustainable
biobased leather substitutes has become a trend over the past few
years. Among the biobased materials, mycelium, the fungal “root”
of a mushroom, is one of the promising alternatives to animal leather,
as a material with tunable physicomechanical properties. Understanding
the effect of humidity on mycelium-based leather material properties
is essential to the production of durable, competitive, and sustainable
leather products. To this end, we measured the water sorption isotherms
on several samples of mycelium-based leather materials and investigated
the effects of water sorption on their elastic properties. The ultrasonic
pulse transmission method was used to measure the wave speed through
the materials while measuring their sorption isotherms at different
humidity levels. Additionally, the material’s properties were
mechanically tested by performing uniaxial tensile tests under ambient
and immersed conditions. An overall reduction in elastic moduli was
observed during both absorption and immersion. The changes in the
measured longitudinal modulus during water sorption reveal changes
in the elasticity of the test materials. The observed irreversible
variation of the longitudinal modulus during the initial water sorption
can be related to the material production process and the presence
of various additives that affect the mechanical properties of the
leather materials. Our results presented here should be of interest
to material science experts developing a new generation of sustainable
leather products.