MycoAcoustics
Research on the sound absorption properties of mycelium-based composites.
Form:
Matter: Mycelium
Fabrication: Molding
Performance: Acoustics
Over the past decade, architecture has begun to show a new emphasis on bio-integrated systems of design and material production. The use of biomaterials as building components can 1) decrease the amount of construction and demolition waste generated, 2) eliminate the reliance on fossil fuels during material manufacturing, and 3) reduce the embodied carbon required for construction. This research intends to generate a more holistic understanding of mycelium-based composites, a biomaterial derived from fungus, and assess its viability for the use as noise control materials. Mycelium-based composites offer a new paradigm of material manufacturing, utilizing waste streams for the growth of the material, requiring little energy to manufacture, and decomposing at the end of its life cycle. This matter-generating process of biofabrication opposes traditional means of material production and extraction through a low impact approach.
This research first presents a material study that explores how substrate variants and fabrication methods affect the sound absorption properties of mycelium-based composites grown on paper-based waste substrate materials. Samples are grown using Pleurotus ostreatus on waste cardboard, paper, and newsprint substrates of varying processing techniques. Measurements of the normal-incidence sound absorption coefficient are presented and analyzed.
The next stage of this research explores the structural capabilities of mycelium-based composites for the purpose of developing acoustic panels. Samples are cultivated using the same growth methodology presented in the acoustic tests and then tested for their flexural strength. A comparison between substrate additives and the strength of the sample is analyzed.
The third stage of this research explores the use of computer simulations to understand how the design and configuration of mycelium-based acoustic panels affect rooms acoustics. Given that mycelium-based composites are novel materials and lack comprehensive acoustical data, we employ the results of impedance tube tests to gather the composites’ sound absorption coefficients. This material-specific data is then used as an input for simulations, using ray-tracing and image-source methods. The simulation results allow for an objective comparison between individual tile patterns, tile aggregation patterns, and the three-dimensional qualities of the panels.
The final stage of this research presents a material study that explores the growth and fabrication of full-scale acoustic panel prototypes made of mycelium-based composites.
Research Team: Natalie Walter and Benay Gürsoy
Publications:
A Study on the Sound Absorption Properties of Mycelium-Based Composites Cultivated on Waste Paper-Based Substrates
Mycelium-Based Composites as Acoustic Architectural Components
Year: 2022
Methodology
This research presents a new methodological workflow to develop advanced biomaterials, test their performance, and design and fabricate acoustic panels. In this workflow, material, form, and performance are in a constant dialogue. The workflow begins with the Cultivation stage, where mycelium-based composite samples are grown. This is followed by the Testing stage, in which the cultivated samples undergo systematic tests to understand the material’s properties and performance. The test results then inform the Design stage, where mycelium-based acoustic panels are designed and simulated for their acoustic performance. The final stage is the Prototyping Stage, in which full scale mycelium-based acoustic panels are fabricated. The results of each stage inform and adapt the methodology of the next stage, while also allowing for a cyclical approach in which the results of each experiment can inform multiple iterations of the same experiment. This methodological workflow allows designers to investigate the performance of both material and form, with a large degree of customization, allowing for modifications depending on the design intent. To that end, this methodology can help establish protocols for material use and implementation within acoustic systems.
Sound Absorption Experiments
Material Preparation
Testing Protocol
Material cultivation begins with substrate selection and preparation. The prepared substrates are then sterilized in an autoclave to mitigate contamination. Once sterilized, the materials are inoculated with P. ostreatus mycelium grown on cotton seed hulls and straw (spawn). These samples are left to grow in a controlled growth environment, first in autoclavable bags for 12 days and then in sterile formworks for 16 more days. Once grown, the samples are dried and heated in a 200 °F oven to kill the mycelium and stop the cultivation process. The samples are then shaped to fit into an impedance tube to test for sound absorption.
Six replicates for each of the samples (material thickness: 38 mm) are tested three times using an impedance tube, specifically the two-microphone transfer-function method, following the standard ASTM E1050-12. Brüel and Kjær’s Impedance Tube Kit (50 Hz–6.4 kHz) Type 4206 is used in this experiment.
Mechanical Tests
Material Preparation
Testing Protocol
Material cultivation begins with substrate selection and preparation. The prepared substrates are then sterilized in an autoclave to mitigate contamination. Once sterilized, the materials are inoculated with P. ostreatus mycelium grown on cotton seed hulls and straw (spawn). These samples are left to grow in a controlled growth environment, first in autoclavable bags for 12 days and then in sterile formworks for 16 more days. Once grown, the samples are dried and heated in a 200 °F oven to kill the mycelium and stop the cultivation process. The samples are then shaped to fit into an impedance tube to test for sound absorption.
The following testing method was developed by Penn State PhD candidate Katy Gerace to test the flexural strength of mycelium-based composites grown on knitted textiles as a part of the project titled “MycoKnit”, which was awarded the SOM Foundation 2021 Research Prize. The testing conditions provided in ASTM D7264, the Standard Test Method for Flexural Properties of Polymer Matrix Composite Materials, are followed.
The samples are tested using an MTS Criterion 50 kN load frame with a 1 kN load cell and 3 pt bend fixtures. The span is set at a constant 150 cm and load is applied with a crosshead displacement of 10 mm/min until failure. Failure is defined as the force necessary to initiate a crack through the thickness of the sample. All samples failed due to cracking near the midpoint. Force vs. deflection data was collected and stress vs. strain curves are obtained following the methodology described in ASTM D7264M. Five samples per test condition are tested to calculate the average.
-
Cardboard
100% fine cardboard substrate material.
-
Sawdust-Cardboard
50% sawdust + 50% fine cardboard substrate material; sawdust is 100% hardwood blend of red and white oak.
-
Switchgrass-Cardboard
50% switchgrass + 50% fine cardboard; switchgrass is obtained from Penn State’s Department of Agricultural and Biological Engineering.
-
Cardboard
100% fine cardboard substrate material.
-
Sawdust-Cardboard
50% sawdust + 50% fine cardboard substrate material; sawdust is 100% hardwood blend of red and white oak.
-
Switchgrass-Cardboard
50% switchgrass + 50% fine cardboard; switchgrass is obtained from Penn State’s Department of Agricultural and Biological Engineering.
Physical Prototypes
The fabrication of the panel prototypes was performed by first CNC-milling a positive wooden form, and then thermoforming the wooden form with PVC sheets to create a reusable plastic negative formwork. Thermoforming uses heat to make the plastic sheet pliable, then uses a vacuum to form the sheet around the positive mold. The benefit of this process is that multiple panels can be grown through the reuse of a single mold. Once the formworks are fabricated, the next step is to prepare the materials. The same growth protocol used for the mechanical tests is followed. The mycelium mixtures are left to grow in a controlled growth environment, first in autoclavable bags for 12 days and then in the thermoformed formworks for 16 more days. Once grown, the samples are dried and heated in an oven to kill the mycelium and stop the cultivation process.
