Development and testing of mycelium-based composite materials for shoe sole applications

Abstract

This research aims to solve problems of solid waste, resource depletion, and material toxicity in the footwear industry. Mycelium, the root structure of mushrooms, acts as a natural glue and binds together substrate materials as it grows outward, offering opportunities for natural composite development. By utilizing mycelium alongside agricultural waste and other natural materials, a fully biodegradable composite with potential shoe sole applications was created. The 4x2 experimental design tested four mushroom species-- reishi, oyster, king oyster, and yellow oyster --and two fabric levels-- with or without a natural fabric mat for reinforcement. Density and compressive strength were measured, and two-way repeated measures ANOVA tests evaluated the relationships between the independent and dependent variables. For density, there was no significant interaction between fabric and species (p=0.117), but the main effects of both species and fabric were significant (p<0.01 for both variables). The fabric contributed to a lower density overall. A post hoc test on species found that the species can be grouped as (king oyster = oyster) > yellow oyster > reishi. For compressive strength, there was no significant interaction between fabric and species (p=0.938) and no significant effect of fabric (p=0.162), but the main effect of species was significant (p<0.01). A post hoc test found that the species can be grouped as: king oyster > oyster > (reishi = yellow oyster). Density was also found to have a positive and significant linear relationship with compressive strength (p=.000), with higher density leading to higher compressive strength. SEM images helped confirm mycelium growth within the composite and around the substrate materials. A comparison of this material to other materials used in footwear indicated that the mycocomposite requires moderate embodied energy in production and scores fairly well on compressive strength. While it has a lower compressive strength than many existing composites or synthetic materials, its sustainable attributes help balance out its performance limitations. This mycocomposite overall showed good compressive strength and provides opportunities for renewable and biodegradable footwear inputs.