Evaluation of Physical Properties of Mycelium-Based Bio Composites for Use As Facade Insulation Material


 Background: To evaluate the usability of mycelium-based materials for construction, first tests were carried out to determine their suitability for thermal insulation. Different substrate compositions were tested for various physical properties. The compositions and experimental setups used are described in the “Methods” section. Results: Materials based on fungal mycelium were found to have promising properties for use in the construction sector. Their thermal conductivities are comparable to those of commercially available ecological insulation materials. As material properties turned out to be dependent on the substrate used for the production of mycelium materials, further optimisation is required. Conclusion: For first preliminary tests [1] to study the performance of mycelium-based materials, different additives (beech wood, rice husks, coffee silver skin, perlite rock) were added to a base substrate to determine their influence on physical properties. Compared to the characteristics of conventional thermal insulation materials, the test results obtained are rather promising and confirm suitability of mycelium-based materials for building. However, further systematic studies are needed to investigate options to improve major properties and to ensure reproducibility of mycelium materials with largely homogeneous properties.

Background: To evaluate the usability of mycelium-based materials for construction, first tests 31 were carried out to determine their suitability for thermal insulation. Different substrate 32 compositions were tested for various physical properties. The compositions and experimental 33 setups used are described in the "Methods" section.

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Results: Materials based on fungal mycelium were found to have promising properties for use 35 in the construction sector. Their thermal conductivities are comparable to those of 36 commercially available ecological insulation materials. As material properties turned out to be 37 dependent on the substrate used for the production of mycelium materials, further 38 optimisation is required.

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Conclusion: For first preliminary tests [1] to study the performance of mycelium-based 40 materials, different additives (beech wood, rice husks, coffee silver skin, perlite rock) were 41 added to a base substrate to determine their influence on physical properties. Compared to 42 the characteristics of conventional thermal insulation materials, the test results obtained are 43 rather promising and confirm suitability of mycelium-based materials for building. However, 44 further systematic studies are needed to investigate options to improve major properties and 45 to ensure reproducibility of mycelium materials with largely homogeneous properties. In the past years, the USA and the Netherlands in particular started to study ecological 56 alternatives to polystyrene-based plastics. These resource-efficient materials are made of 57 organic substrates that are interconnected by the root network of conventional fungi, the so-58 called mycelium. Having killed the fungal organism by drying, solid material results, whose 59 properties are similar to those of polystyrene products. Such material has already been 60 commercialised as an alternative to polystyrene-based packaging material [5]. First studies 61 revealed that it also has a big potential for façade insulation of buildings. However, systematic 62 fundamental investigations confirming suitability still remain to be carried out. 63 It is the authors' central concern to identify fundamental properties of mycelium-based 64 materials and to present possibilities to specifically control major properties. The authors will 65 focus not only on the thermal behaviour, but also on other physical characteristics. The

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To produce the material specimens, a commercially available substrate was used, which 72 mainly consists of crushed hemp straw on which oyster mushroom (Pleurotus ostreatus) was 73 grown. Various organic and inorganic additives were added to this pre-cultivated material in 74 order to study their influence on major physical properties. Among these additives were beech 75 wood shavings, rice husks, coffee silver skins, and perlite rock. Pressed (compacted) and non-76 compacted specimens were studied. The most important physical property of insulation materials in the building sector is their 84 thermal conductivity. The specimens covered by this paper were analysed for thermal 85 conductivity according to DIN EN 12664 [6] using the λ-Meter EP500e (see Figure 1 (right)). 86 The thermal conductivities measured at a specimen centre temperature of 10°C in both dry 87 (furnace drying) and wet specimens (equilibrium moisture at 23°C and 50% relative humidity) 88 are represented in Figure 1 (left).  "natural" surfaces covered by a mycelium layer (see Figure 3). The water absorption coefficient of mycelium-based material with a production-related 130 "natural" surface is below 1.0 kg/(m²·h 0.5 ). Specimens, whose surfaces were cut by a saw had 131 up to 50% higher water absorption coefficients. A problem encountered in the tests was 132 mould formation in the area of the capillary height after 24 hours already. In principle, production of mycelium-based materials is not complicated. However, production 136 of the specimens has shown that mycelium-based material is highly susceptible to mould 137 formation. Hence, highly sterile conditions are required when using mycelium-based 138 materials. 139 Investigation of capillary water absorption revealed that the material is of hydrophobic 140 character. Tests without the "natural" mycelium coating produced far higher water absorption 141 coefficients. For this reason, hydrophobicity is explained by this outer layer. The main 142 constituent of the outer mycelium layer is chitin, a water-soluble polysaccharide. In case of 143 longer water contact, the chitin may be assumed to dissolve and water absorption properties 144 of the surface will change. Specimens, whose surfaces were cut by a saw, exhibited first mould 145 formation after 24 hours already. Hence, cutting of the materials is not recommended. Due to 146 the simple and flexible production process, it is theoretically possible to produce custom-147 made elements of any shape, but local conditions may require unplanned adaptations, which 148 is why this must be considered a drawback. 149 Recently, the fire behaviour of insulation materials was subject of many discussions. Most  The studies reported here have shown that properties of mycelium-based materials 158 considerably depend on the composition of the substrate used. Addition of beech wood 159 shavings to the base substrate produced a stable structure, but specimens were more difficult 160 to cut with a saw. 161 The results obtained confirm that mycelium-based materials are suited in principle for use as Water vapor diffusion resistance µ of mycelium materials ranges from 40 to 50 and may be 168 compared with that of polystyrene products. Using an exemplary wall structure, components 169 were verified and compliance with the requirements outlined in DIN 4108 was confirmed [1]. 170 The water absorption coefficient depends on the surface properties of mycelium-based 171 materials. If materials have to be cut, measures should be taken to protect the cut areas 172 against moisture. 173 9 Kotan_Dehn_final_20210826.docx

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As little is known about the use of mycelium-based material for building, the tests reported 176 here were carried out in two stages. Various substrate compositions, production methods, 177 and testing methods were used in preliminary experiments. In the main experiments, the 178 methods were optimised based on the findings obtained from the preliminary tests and 179 important physical properties were determined. 180 The basis of all substrates was a pre-cultivated substrate made of crushed hemp straw on 181 which the oyster mushroom (Pleurotus ostreatus) was grown. This base substrate was mixed 182 with various additives in the form of organic waste or by-products. Finally, beech wood 183 shavings, rice husks, and coffee silver skin additives were used. One substrate was mixed with 184 bloated perlite rock. Moreover, wheat flour was added to all substrates in order to provide 185 the fungus with the carbon chains needed for growth. Figure 4 shows the substrate 186 compositions selected (left) and the specimens produced. Thermal conductivity was measured for dry and wet specimens at specimen centre 202 temperatures of 10°C and 23°C. 203 Water vapour diffusion resistances were determined according to DIN EN 12086 [8]. For this 204 purpose, cylindrical specimens were embedded in wax on one side and then fixed on a vessel 205 with calcium chloride desiccant in an air-tight manner. From the mass variations measured, 206 the water vapour diffusion coefficient was determined for subsequent calculation of the water 207 vapour diffusion resistance and the water vapour diffusion-equivalent air layer thickness. 208 To determine the capillary water absorption behaviour, area-related water absorption was 209 determined after short partial immersion and the water absorption coefficient was calculated 210 taking into account the root of the time according to DIN EN ISO 15148 [13]. The tests were 211 carried out using specimens with an undamaged outer mycelium layer and specimens with a 212 saw-cut surface having no "natural" mycelium layer.