Networks formed of natural nano-fibrils are an appealing approach to integrate the advantages of nano-scale fibers with sustainable raw materials. Whereas cellulose nanofibrils are already widely applied, nanofibrillated chitin has lagged behind this development. Commonly, chitin is derived from crustaceans, requiring harsh and prolonged chemical and mechanical processes for the isolation of nanofibrils. Opposed to that, fungal chitin fibrils, coming in a natural chitin-glucan (CG) complex with glucan combining the strength of chitin and the toughness of glucan, are easily accessible by mild extraction methods and natively nano-sized. Isolation of such fungal chitin nanofibrils (FChNF) does not require energy-intensive extraction methods as necessary for the extraction of cellulose nanofibrils or chitin nanofibrils of crustacean origin. FChNF can also be derived from mycelium, the vegetative part of fungi. Thus, fungal growth can be utilized as low-cost source for on-demand generation of natural nanofibrils that are subsequently utilized in the formation of nanostructured networks. Here, we extracted natural polymers from various species, e.g. white button mushrooms (Agaricus bisporus), tree-bracket fungi (Daedaleopsis confragosa), and mycelium grown on agricultural byproducts, i.e. sugarcane molasses, utilizing a mild alkaline extraction process. Isolated polymer fibrils were processed into nanopaper networks and polymers, fibrils as well as nanopapers characterized regarding their composition, surface characteristics and mechanical properties. Fungal extracts were readily disintegrated into nanofiber dimensions by low-energy mechanical blending, preserving the native quality of the CG complex. Mechanical properties of CG nanopapers were determined by the nanostructure of the network with glucan playing a crucial role. Furthermore, hydrophobic surface properties originated from the composition of the nanopapers. Biopolymers prepared from these resources are applicable in a wide range of applications from packaging over filtration membranes to composites.

Fungi and mycelium-based nanofibril networks

ACS Spring 2022

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