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Abstract Carbons form critical components in biogas purification and energy storage systems and are used to modify polymer matrices. The environmental impact of producing carbons has driven research interest in biomass‐derived carbons, although these have yield, processing, and resource competition limitations. Naturally formed fungal filaments are investigated, which are abundantly available as food‐ and biotechnology‐industry by‐products and wastes as cost‐effective and sustainable templates for carbon networks. Pyrolyzed Agaricus bisporus and Pleurotus eryngii filament networks are mesoporous and microscale with a size regime close to carbon fibers. Their BET surface areas of ≈282 m2 g−1 and ≈60 m2 g−1, respectively, greatly exceed values associated with carbon fibers and non‐activated pyrolyzed bacterial cellulose and approximately on par with values for carbon black and CNTs in addition to pyrolyzed pinewood, rice husk, corn stover or olive mill waste. They also exhibit greater specific capacitance than both non‐activated and activated pyrolyzed bacterial cellulose in addition to YP‐50F (coconut shell based) commercial carbons. The high surface area and specific capacitance of fungal carbon coupled with the potential to tune these properties through species‐ and growth‐environment‐associated differences in network and filament morphology and inclusion of inorganic material through biomineralization makes them potentially useful in creating supercapacitors.

Macroporous polymers and nanocomposites remain popular materials due to their low densities and unique interconnected pore structures. The determination of mechanical properties in relevant loading conditions, such as shear, remains largely underexplored due to the comparative complexity of such analysis compared to simple compression tests. We investigated the use of the Arcan test to induce uniform biaxial stress in such materials and provide insight into the effect of porosity and silica particle reinforcement on shear properties and fracture toughness of high/medium internal phase emulsion templated macroporous polymer nanocomposites, called polyHIPE/MIPEs. Increasing foam densities were associated with greatly improved tensile and shear properties. Improvements in shear strength and modulus were also noted in polyMIPEs reinforced with as little as 5 wt.% silica nanoparticles, although any increase in tensile properties was lacking. Fracture toughness was investigated using an assumed Poisson's ratio. Decreasing the porosity of macroporous polymers and increasing particle loading resulted in considerable improvements in fracture toughness. These results illustrated the potential of the Arcan test as a simple and effective method for investigating otherwise rarely reported loading conditions in macroporous polymers and nanocomposites.