Investigation of Mycelium-Miscanthus composites as building insulation 1 material

– Good insulation materials have low thermal conductivity which is mainly related with 8 the density of the material. Bio-composite insulation materials contribute to reduce the 9 environmental footprint of buildings. The main goal of this study is to study the effectiveness of a 10 self-growing, bio-composite building insulation material made of Miscanthus x giganteus and the 11 mushroom Mycelium. Different mix proportions of Miscanthus and Mycelium were considered to 12 identify the most suitable mixture to produce a porous composite which has a lower density. 13 Scanning electron microscopy images were used to evaluate the microstructural geometry of the 14 composite material. Thermal conductivity test was conducted on eight composite plates, and the 15 results showed that the thermal conductivity of this new material is between 0.0882 and 0.104 16 Wm -1 K -1 . Moreover, other experiments were carried out to characterize the density, compressive 17 strength and water absorption. In addition, fire resistant tests on composite plates with and without 18 render were conducted, and it was found that the composite plates belong to the category EI15 19 according to the EN13501-2:2003. The initial results were found to be satisfactory to make a 20 sustainable insulation material out of Miscanthus and Mycelium.


INTRODUCTION
Depletion of natural resources, such as sand and gravel, is occurring at an alarming rate because 27 the current pace of consumption in the construction industry is not sustainable [1]. Besides, the 28 extraction, processing, manufacturing and transportation of building materials have the highest 29 contributions in carbon emissions related to the construction industry. In order to protect the As mentioned above, Mycelium is the vegetative part of mushroom. In this study, Mycelium was 119 obtained from Ganoderma resinaceum mushroom. The Mycelium from the Ganoderma family 120 develops better than other mushrooms. Only the grains of the Mycelium were used to envelop the 121 Miscanthus ( Figure 2). The Mycelium penetrates its nutrients by physical pressure and not 122 enzymic secretion to break the host's polymers in order to transform them into more easily 123 transportable nutrients such as sugars. In this study, the selected nutrient substrates are pure 124 cellulose biopolymers and cellulose-potato dextrose both are composed of potato Infusion solids 125 and Dextrose (sugar). This choice was made because of the abundance and availability of this 126 natural polymer for cellulose and for the latter, it is because this medium is the most common used 127 for the development of mushrooms thanks to its composition based on sugar easily digestible by 128 the Mycelium. Because of their similar chemical form as well as by their surface homogeneity it 129 is expected that these two nutritive bases allow a hydrolysis without gene with the Mycelium to 130 guarantee a growth which will not depend on the nutritive base to provide a homogeneity of the 131 material [18]. It does not need additional energy input to propagate. It only needs the usual fungus 132 propagation conditions to grow (high humidity, the sample should stay in a dark place and stay 133 under room temperature). Sterilization is important for the growing process of mycelium, because 134 other spores could affect it or worse kill it. Thus, the development environment should be sealed 135 to protect it from contamination [18]. In addition to these two main materials, as mentioned above, potato starch extracted from potatoes 140 ( Figure 3) were used as substratum of Mycelium, which is the base material used by the mycelium 141 to grow. Here starch was used for the Mycelium to grow as a web. The potato starch itself contains 142 large oval spherical granules, which size is between 5 and 100 μm.    x 40 mm x 160 mm and covered with a sterilized plastic wrap, as shown in Figure 5(a).

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Since a dark environment is helpful to the growth of the mushroom, the samples were kept in a  Miscanthus. In this phase, Mycelium grows the most due to higher amount of starch available.

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Thus, it can be assumed that the samples will have firm shape after the first growing phase.

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The dimensions and weights of the demoulded test samples were measured, and the samples were 182 then put separately in sterilized bags and sealed in order to begin the second growing phase.

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Although the samples had a stable shape at the end of the first growing phase, it was observed that 184 the part of the sample which was against the mould was not enveloped by the Mycelium ligaments.

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Thus, the second growth phase is aimed to reinforce the structure of Mycelium which leads to 186 stiffer and stronger final product. Therefore, the samples were put in the same cabinet again as in  After first phase After second phase After drying phase Figure 6. Average density of all the mixtures after each phase 224 As the mixtures G0.3_M1_P0.1 and G0.7_M1_P0.1 present a low-density, for these mixtures an 225 excellent thermal insulation capacity could be expected. However, since for mixture 226 G0.3_M1_P0.1 sample less Mushroom, that is 45g, is used, it was identified as well-balanced mix 227 proportion for being applied in a lightweight Mycelium-Miscanthus thermal insulation board.   The morphology of the Mycelium-Miscanthus composite is shown in Figure 9(a). It shows that 257 there is Mycelium growth between and around the Miscanthus fibers, successfully embedding the 258 Miscanthus into the composite. Figure 9  recorded. The compression test was continued until the specimen reaches 10% relative 276 displacement, and the compressive strength was defined according to [24] as the stress at 10%  Since the composites are hydrophilic, the durability of the material could be affected when the 288 studied Mycelium-Miscanthus composites is used as insulation material. Therefore, the water where M1 is the initial dry mass and M2 is the water-soaked mass.

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The initial dry mass of the sample was 0.0555 kg. Figure 12 shows the observed results on the

Specimen 1 Specimen 2 Specimen 3
Specimen Average usually used in internally dry conditions, the weight increase occurred within first few seconds is 302 not a significant problem [26], as for other insulation materials too, a render will protect the 303 composite from environmental impacts. Once the absorption test was completed, the test sample was kept in the water for a certain period 307 to observe the possible changes and developments on the sample. Although the composite was 308 observed during 1 month, no development of Ganoderma was observed. After 1 month, a sample 309 was cut in half to inspect inside, and it was observed that Ganoderma had not developed inside the 310 composite as well, as shown in Figure 13. It is apparent that despite the water is partially raised in 311 the sample, the development of the mold stops at the outer space ( Figure 13). This, it can be 312 concluded that drying the mixture at 80 ˚C effectively kills the fungus.

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After having studied the mixture properties with prism samples, Mycelium-Miscanthus plates were 318 produced using the same procedure and the same ratios as for the prisms, described in Section 2.2.

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The only differences were related to the volumes and the formworks used. The plate dimensions 320 were 500 mm x 500 mm x 70 mm. G0.3_M1_P0.1 mixture was used to manufacture the bio-  In total, six plates were manufactured. Plates 1 to 4 were made produced without a render, while 326 Plates 5 and 6 were covered with a render. Two layers of render were applied on those two plates 327 according to ETAG-004 [27]. A 15 mm thick layer of Weber DUR 137 was used as a base coat 328 layer and 10 mm thick of Weber TOP 200 was put on the first render layer as a finishing coat.

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After the application of base layer, a 5mm x 5mm grid was placed on the top of the base layer as 330 reinforcement. Before application of Weber TOP 200, it was ensured that the first layer is 331 completely dry and dust free. Figure 15 shows the manufactured plates with two layers of render. al. [21] showed that Mycelium-based bio-composite has a thermal conductivity between 0.05 and  Plate number 6 5 They were first left for 76 days outdoor in order to study the impact of humidity and temperature 345 changes as well as and UV radiation on them. It was observed that the renders on the plates were 346 unaltered. There were neither cracks nor curvatures visible. However, after six weeks, a bump 347 appeared on the Plate 6. Figure 17 shows the variation of weight of the Plates 5 and 6 during the 348 experiment. In general, it was observed that the plates did not change a lot, which shows that the  In the next step, the insulation capabilities of composite plates were studied by measuring their 353 thermal conductivity. The device Taurus TLP800/900 was used to determine the thermal 354 conductivity of Mycelium-Miscanthus composite plates. Figure 18(a) shows the thermal 355 conductivity test carried out by the Taurus TLP800/900 device on the composite plate according 356 to ISO 8302/EN 1946-3. In total, three tests were carried out. For the first test, two composite 357 plates (Plates 2 and 4) were used at the same time, as illustrated in Figure 18(b), while the second 358 test was carried out for a single composite plate (Plate 1), as illustrated in Figure 18(c). The third 359 test was carried out using the two composite plates with render (i.e. Plates 5 and 6) after their 360 exposition to outside environmental conditions for 2 months. In Figure 18  shown in Figure 18(d). Moreover, the composite plates were insulated on the four sides so that Thermocouples attached on the test sample 379 The thermal conductivity of each plate was measured at three different mean temperatures because 380 of the temperature difference between the heating plate and the cooling plate. The λ-value is 381 calculated from the power which is put into the heating plate, the thickness of the sample and the temperature difference. It gives the thermal conductivity of a material in the unit of Wm -1 K -1 . The 383 obtained results are plotted in Figure 19. From these results, it can be seen that the λ-values for 384 plates 2&4, 1, and 5&6 are 0.0882, 0.104 and 0.121 Wm -1 K -1 , respectively. Thus, it is clear that softwoods and gypsum about 0.08 [32], 0.1 [33], 0.12 [34]and 0.17 [34] Wm -1 K -1 , respectively.   wool started to burn after 40 minutes. Figure 20 shows the plate before and after it was burned for 405 40 minutes.  Figure 21 shows the captured temperature progression by the thermal camera during the fire test.

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It can be seen that the heat from the flame took about 7 minutes to get to the top of the plate and 412 another 33 minutes to burn the cotton wool and create an opening on the top of the plate. Moreover, 413 Figure 22 depicts the variation of temperature at two points, one is on the cotton wool (P1) and 414 another is on top of the plate just close to the cotton wool (P2), during the fire test. It was observed 415 that the temperature at point P1 slightly decreased until 22 minutes. This is due to the high amount 416 of fume, which was created during the test. Then, the same procedure was conducted on a plate with render. The side which has no render was 428 placed over the flame, as shown in Figure 23(a). It was burned for 1 hour and 10 minutes. Since 429 the sample did not show any combustion over this period, the test was then stopped. It was 430 observed that the cotton wool did not burn like in the first test, as shown in Figure 23(b), because 431 the fire did not go through the plate. However, it can be seen that the bottom of the plate has 432 burned, as shown in Figure 23(c). the temperature of the non-exposed side of the element does not rise over 140 ˚C [35].