In Situ Calcium Carbonate Mineralization of Mycelium Composites: Processing Challenges and Physical-Mechanical Property Implications

The potential for calcium carbonate (CaCO₃) mineralization of mycelium composites (MCs) using a procedure commonly applied to natural wood is explored. The effects of this mineralization on the structural, thermal, and compressive properties of the materials are explored, revealing unexpected outcomes that challenge prior observations reported for mineralized wood. CaCO₃ was deposited into MCs via an in situ, vacuum-assisted mineralization process using calcium acetate and sodium bicarbonate, with treatment durations of 5 and 24 h, resulting in mineral contents of ∼1 and 10 wt %, respectively. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and selective area electron diffraction (SAED) confirmed the formation of CaCO₃ crystals, identifying the predominant polymorphs; namely vaterite and calcite. Notably, mineralization led to a reduction in the thermal stability of the composites, suggesting a potential catalytic effect of CaCO₃ on the thermal degradation of the MC. Compressive testing of the MCs further indicated a decline in their mechanical strength following mineralization, likely attributable to structural alterations induced during the process. In addition, Water Contact Analysis (WCA) showed a substantial decrease in surface hydrophobicity following mineralization, with contact angles reduced by more than 50% relative to untreated MCs. This study underscores the need for careful evaluation of mineralization strategies, as they may lead to deterioration rather than enhancement of MC performance. This is found to be contrary to many other previous reports on the mineralization of biomass materials.