3.1.2. Structural Integrity

The structural integrity of the composite material largely relies on the structure of the substrate material and how well mycelium can grow throughout the substrate. The Sample FNL (fine newsprint) did not hold together once dried, cracked, and crumbled, as seen in Figure 6a. A possible explanation for the deterioration is the structure of the fine newsprint. When pulverized, the newsprint became very fine dust, while the pulverized paper and cardboard maintained more of their structure. After shaping the materials using industrial tools, the materials' structural integrity was affected, as the fungal skin is a large component holding the material together. The Sample SPH (shredded paper), once cut with a saw, could not yield accurate results in the impedance tube because of its structural integrity, as seen in Figure 6b. Therefore, no further tests were conducted with the FNL, FNH, SPL, and SPH Samples.

Once all the samples were cut open, the inner growth of the samples was analyzed. The samples were observed to have higher mycelial growth on the outer surface and less mycelial growth internally. This could be related to the absence of light and air and the heat produced by mycelium during growth [15]. While the shaping of the samples was necessary for the impedance tube tests, it is worth noting that for the purpose of acoustic panels, shaping/cutting the samples negatively affects their durability and structural integrity.

It is possible that a combination of different substrate materials would lead to more mycelium growth and stronger material. Further research can be conducted to assess the mechanical and physical characteristics of mycelium-based composites grown on different combinations of paper-based waste substrates.
