Using an Invasive Plant (Japanese Knotweed) for Mycelium-Based Thermal Insulation Composites

Mycelium-based composites (MBCs)-biomaterials made from fungal-inoculated substrates-are promising candidates to replace conventional rigid thermal insulation panels. However, many MBCs are made from hemp, a plant material that is quite difficult to source in many countries for regulation reasons, and mobilizes agricultural fields at the expense of food and feed crops. Meanwhile, many of our natural and urban ecosystems are subject to invasion by plants that are just burnt or even left in place, while they may be very good substrate for MBCs. This study investigated the comparative physical and thermal properties of MBCs derived from two distinct lignocellulosic feedstocks: hemp shives (a traditional material) and biomass from the highly invasive species Reynoutria japonica. Polyisocyanurate (PIR) was included as a synthetic benchmark. The MBCs produced from R. japonica demonstrated as low a thermal conductivity as the hemp MBCs in our internally developed method, but also as the PIR standard. However, they exhibited suboptimal physical characteristics: higher bulk density (166 vs. 128 kg/m³ for hemp) and significantly higher water absorption (7.5% vs. 3.5% volume uptake after 2 min). This suggest that they are a less viable alternative to hemp-based MBCs for heat insulation applications.