Naturally grown mycelium-composite as sustainable building insulation materials
Introduction
In light of its important role in addressing environmental issues and achieving economic benefits, energy saving has received increasing attention in the recent years. The heating and cooling energy used for building operations account for almost one third of the total energy consumption in the world (Sutcu, 2015; Kim et al., 2017; Balaras et al., 2000). Thermal insulation materials are utilized in the building envelope to improve the energy efficiency, by reducing the thermal loads both in the hot and cold climate zones (Gauvin and Vette, 2020). The insulation layer provides a border between the indoor and outside environment, ensuring the thermal comfort of the inhabitants and reduces energy usage in operating the building (Schiavoni et al., 2016).
Synthetic or petroleum-derived materials with good thermal performance, such as glass wool (Tatematsu et al., 2014), expanded polystyrene (EPS) (Lakatos and Kalmár, 2013), and polyurethane (PU) foam (Kuhn et al., 1992) etc., are widely used as building insulation materials. However, their manufacturing processes incur carbon footprints. In addition, some of the synthetic or petroleum-derived materials may contain harmful substances, limiting their application for building construction due to possible health concerns. Furthermore, most common types of synthetic foams are not biodegradable and lead to generation of large amount of waste at the end of their service life (Elsacker et al., 2021). In other word, synthetic insulation materials have negative impacts regarding their manufacturing, application, and recycling, causing damage to the environment and to human health. Therefore, the need for sustainable buildings calls for the development of eco-friendly insulation materials. Fungal mycelium is an attractive option to generate a bio-composite, because it features excellent thermal performance and biodegradability (Zhang et al., 2021a). Fungal mycelium is a network of interlaced hyphae emerging from the fungal colonization of feedstocks. A variety of feedstocks (i.e., sawdust (Appels et al., 2019), rice hull (Jones et al., 2018a), white grains (Jones et al., 2018b), and wheat straw (Ghazvinian et al., 2019)) could all be utilized to produce mycelium composites. The grown mycelium-composite materials, which are sustainable lightweight materials, have been studied as alternatives to the synthetic and petroleum-derived foams for thermal insulations (Jones et al., 2018a, 2018b, 2020; Girometta et al., 2019). The mycelium-composite material has a low density of around 0.05 g/cm3 (Islam et al., 2017), which is in the range of the density of 0.015–0.075 g/cm3 for EPS foams (Schiavoni et al., 2016). Low thermal conductivity (0.05 W/(m·K)) and high specific heat capacity (10.2 kJ/(kg·K)) have also been reported on mycelium-composites, which are comparable to conventional insulation materials (Schiavoni et al., 2016; Amstislavski et al., 2020; Xing et al., 2018). The mycelium-composite bricks and panels are often categorized as insulation foams because of their high porosity and slight rigidity (Girometta et al., 2019). Aside from brick and panel foam, the mycelium-composite can be built as sandwich composite, which is a popular form of applications for building insulation (Ziegler et al., 2016; Silverman, 2018; Jiang et al., 2016). Jiang et al. (2016) investigated a novel manufacturing system that grows using a core of mycelium-composite foam sandwiched between two laminate layers of fabric or mycelium mat. Additional innovations include a robotically manufactured system that grows large-scale mycelium composites, and the discovery of self-healing in these composites during the fabrication process (Elsacker et al., 2021). Manufacturing with 3D printing has likewise been studied, where fungi were allowed to grow inside the printed samples (Bhardwaj et al., 2020) to facilitate customized application of mycelium-composite material in buildings.
Previous studies have noted the moisture behavior and the mechanical properties of mycelium composites, but not the relationship between them. The impact of moisture on the mechanical properties of mycelium composites are the focus of my study. The growth behaviors of mycelium in the composites are dependent on its particular strain and feedstocks, as well as the density of colonized feedstocks used for incubation. The mycelium developed around feedstocks are hydrophobic (Zhang et al., 2021b), which affects the composites’ overall water absorption. Both the densities and water contents of the mycelium composites are key factors on their measured properties. Water absorption has been observed to cause cracks in the composites which compromises their mechanical properties and durability (Bui et al., 2020). The influence of density on the mechanical properties of mycelium composite has been studied, including the modulus and ultimate failure strain, and were summarized in (Jones et al., 2020). Compression tests were conducted on the mycelium composites under ambient conditions, and the results show that composites with a dense fungal biomass had a higher compression stiffness (Elsacker et al., 2019). A previous study also found that the water absorption and mechanical properties of mycelium composites were influenced by different fabrication methods, types of feedstocks, and fungal species (Appels et al., 2019). However, no studies have analyzed the moisture-dependent mechanical properties of mycelium composites. Besides, although the thermal properties of mycelium-composite material have been investigated, their performance when applied as insulation materials in the building envelope have not been sufficiently evaluated.
In order to advance possible avenues in this field, this study investigated the mechanical and thermal properties of mycelium composite under a variety of environmental conditions. The energy saving performance of mycelium-composite insulation for buildings under different climate zones is evaluated using Energy Plus, an industry standard for building energy performance assessment. Mycelium-composite insulation was produced with an edible fungus (Pleurotus ostreatus) that was cultivated in rye berries feedstock. The microstructure and chemical elements mapping of grown mycelium composite were studied by Scanning Electron Microscope/Energy Dispersion Spectroscopy (SEM/EDS). The mechanical behaviors and failure modes of mycelium composites with different density were investigated after exposure to different levels of relative humidity. EnergyPlus was utilized to conduct the energy usage simulations based on the experimental measured results of the physical and thermal properties of mycelium composites. Comparative analysis was conducted on building models specifically between using mycelium-composite insulation, which is naturally derived, and traditional natural insulation materials, i.e., lightweight expanded clay aggregate (LECA) and expanded vermiculite (EV). In addition to comparing materials, this study uses these building models to illustrate the impact of different climate zones on energy consumption. The results of both simulations indicate that the mycelium composite performs better than traditional natural insulation materials under different climate conditions, with the exception of the very hot climate zone. Mycelium composite insulation is a new and innovative form of natural insulation whose energy performance compared favorably to the traditional insulation materials. It therefore presents a more environmental benign and sustainable building insulation option.
Section snippets
Sample preparations
The fungi spawn of Pleurotus ostreatus, which is free from injurious diseases and pests, was utilized in this study. The fungi spawn containing numerous hyphal vegetative tissue and spores was purchased from the Mushroom Spawn Laboratory at Pennsylvania State University. Composite samples were prepared by growing fungi spawn with rye berries. The procedure of samples preparation is demonstrated in Fig. 1. A filter patch bag with 454 g of rye berries was sterilized at 121 °C for 2.5 h by using
Model and methodology
The building energy assessment was simulated by EnergyPlus version 8.9.0, which is a flagship software developed by the Lawrence Berkeley National Lab of the US Department of Energy (Hu and Yu, 2020). The performance of EnergyPlus has been validated with the experimental results and other widely used energy simulation software (Witte et al., 2006). It includes three major components, i.e., a simulation manager, a heat and mass balance simulation module, and a building system simulation module (
Analysis of energy performance
The model of buildings with mycelium-composite insulation or with conventional insulations (LECA, EV) was established in the 8 U.S. climate zones. First, to illustrate the general observation, the daily temperature on the inner roof surface was evaluated in the building with mycelium-composite insulation or conventional insulations located in Albuquerque, NM during the heating or cooling seasons. Then, buildings with different insulators under various climate thermal conditions were modeled and
Conclusions
This study explored the potential of biologically growing mycelium composites as natural building insulation materials. The mycelium composite bricks were naturally grown with edible fungus, Pleurotus ostreatus, using rye berry grains as biodegradable substrates. Their moisture-related mechanical properties were investigated. Additionally, the energy performance of buildings with mycelium-composite insulation was analyzed with EnergyPlus and compared with traditional natural insulation
CRediT authorship contribution statement
Xijin Zhang: conduct experiments, data analysis, and Energy plus analyses, write the initial manuscript. Jianying Hu: provide training on Energy plus analyses. Xudong Fan: assist with experiments. Xiong Bill Yu: conceptualize the study and guide the implementation, proofread the manuscript.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
The authors would like to thank Jim Berilla for his assistance in thermal properties measurement. Shifa Zhong for assistance with the EDS analysis. The SEM and EDS data were obtained at the Characterization Facility of the Swagelok Center for Surface Analysis of Materials (SCSAM), Case Western Reserve University.
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