Session: K7-01: THERMOPHYSICAL PROPERTIES I

Paper Number: 131982

131982 - Measuring Thermal Conductivity of Mycelium-Based Thermal Insulation Materials Produced With Locally Available Organic Waste Products As Substrate 

Abstract: 

According to the US department of energy, a majority of residential and commercial energy use can be attributed to the heating and cooling of buildings. Insulation is important in preventing energy losses from the buildings being heated and cooled. Most insulation materials are petrochemical-derivative and pose a risk to human and environmental health during installation, occupancy, and demolition of old buildings. Fungal mycelium materials, commonly referred to as “mycomaterials” are a class of sustainable biomaterials with unique material properties, created by growing mycelium on an organic substrate. The desirable material properties of mycomaterials are their foam-like structure, strength under compressive load, low thermal conductivity, superior fire retardant characteristics, hydrophobic surface, and acoustic performance. Additionally, mycomaterials are completely biodegradable without commercial composting facilities, and pose no risk to human or environmental health. Mycomaterials are sustainable because they can be grown with agricultural waste, and do not require high temperatures during manufacturing.

A 27 in³ cube of reishi-based hemp-herd mycomaterial sample could increase density by 50% under 22.5psi of pressure before fracture. Several studies have measured the thermal conductivity of mycomaterials to be between 0.06W/mK and 0.03W/mK on average, and as low as 0.02W/mK, outperforming the commonly used extruded polystyrene (XPS) or polyurethane foam. Mycomaterials have been shown to remain stable at temperatures up to 300°C before thermal degradation. Other studies have shown that although mycomaterials ignite at similar speeds to XPS foam, they emit significantly less carbon dioxide, carbon monoxide, and smoke density due to higher rates of char formation. Mycomaterials feature low water uptake, and panels made from this material could be washed in a typical household sink without damage. Rudimentary loss transmission tests performed on 1” thick, square foot acoustic panel samples made from reishi mycelium grown on various different substrates suggest an 80dB decrease in sound transmitted compared to the control. This is comparable to typical commercially available acoustic panels made of plastic foam. For mycelium-based thermal insulation to be integrated into buildings, the thermal conductivity of each sample made from different fungal species and different substrates must be determined. Rapid testing of samples is integral to quickly determine the combination of fungal species and locally available organic waste substrate that would result in the lowest thermal conductivity and other desirable material properties.

Determining the thermal conductivity of low-k materials is commonly done with transient methods that can provide a fast and accurate evaluation of thermal conductivities of hyper-specific locations through a sample material. However, to better estimate the real-world performance of a building insulation material, testing for the average thermal conductivity through a material using steady-state techniques can be preferable. Additionally, many transient techniques rely upon a thin film of water for even distributions of heat to be applied on the tested materials surface, which is ineffective for mycomaterials which have hydrophobic surfaces. Current steady-state methods have long test-times and are often not suitable for low-k materials due to heat applied through the sample material being lost to the surrounding environment instead of traveling through the sample. The present work seeks to demonstrate measurement of the thermal conductivity of mycomaterial samples accurate within 10% using steady-state methods different from but inspired by the “guarded hot-plate” approach. It is anticipated that such a steady-state approach that utilizes one-dimensional heat conduction and Fourier’s Law can achieve accurate measurement of k by using samples with surface areas on the order of 0.05m2, low energy input (qin), an isothermal boundary layer and vacuum-insulation to isolate the system and minimize error with  heat lost to the surroundings.

Presenting Author: Brandon Bunt The Cooper Union

Presenting Author Biography: Brandon Bunt is a graduate student in mechanical engineering at the Cooper Union studying the thermal conductivities of mycelium-based thermal insulation.

Authors:

Brandon Bunt The Cooper Union
Kamau Wright The Cooper Union
Benjamin Davis The Cooper Union