Exploring the potential of filamentous fungi as coatings for aerospace aluminum alloys
M.C. Ablonczy (TU Delft - Aerospace Engineering)
S.J. Garcia – Mentor (TU Delft - Novel Aerospace Materials)
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Abstract
Filamentous fungi grow large networks of biomass with minimal energy input. This
biomass consists of polysaccharide-based filamentous networks and adherent extracellular polymeric substances (EPS). Recent reports show that this biomass can be formed into plastic-like thin film materials. Further, non-filamentous fungi have been applied as living coatings on wood. Even so, filamentous fungi remain unexplored for coating applications. This work fills that gap by studying how a selected filamentous fungus (Schizophyllum commune) and its lab-produced biomass interact with aerospace aluminum alloys, and to explore their potential as a sustainable resource to create coatings.
Two complementary routes were explored in this work. In the first one, S. commune was allowed to grow—under controlled conditions—on the surface of bare aluminum alloys of different compositions and surface treatments. The growth extent, filament density, and structure were investigated as a function of the underlying metal composition, surface treatment, and nutrient availability. In the second route, thin-film coatings were produced from processed biomass extracted from liquid cultures of S. commune. The quality of the consolidated films and their scratch resistance and adhesion as a function of a range of processing parameters and aluminum surface treatments was investigated.
S. commune grew further and more densely on AA6082 than on AA2024 and AA7075.
Differences decreased after grinding, which suggests that the alloy-dependent near-surface deformed layer and alloy composition heavily influence fungal growth. The in-situ-grown fungi led to intense local surface corrosion and weakly adhered biomass. Alternatively, films produced from processed liquid culture biomass led to semi-transparent coatings with microstructure dependent on the processing conditions and fungal extract used. Although processing steps led to improvements in scratch resistance and porosity, coating macroporosity remained high and insufficient for barrier requirements. Surface treatments led to clear improvements, but even then, film adhesion remained well below that of more broadly studied and developed biopolymer coatings (>10x better adhesion). This research showed the potential of fungi to create films on aluminum alloys with ample room for improvement toward fungi-based coatings. Future research should focus on more extensive species screening, adhesion optimization, decreasing porosity, and better understanding fungi-metal local interactions.