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

## TL;DR

This paper explores how adding calcium carbonate to mycelium composites affects their properties, finding unexpected negative impacts on thermal stability and mechanical strength.

## Contribution

The study reveals that mineralization of mycelium composites can lead to deterioration rather than enhancement of material performance.

## Key findings

- Calcium carbonate mineralization of mycelium composites resulted in the formation of vaterite and calcite polymorphs.
- Mineralization reduced thermal stability and mechanical strength of the composites.
- Surface hydrophobicity of the composites decreased significantly after mineralization.

## Abstract

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.