Title: Mycology Matrix Composites Proceedings of the American Society for
Composites—Twenty-Eighth Technical Conference
Authors:
S. Travaglini
J. Noble
Professor PG Ross
Professor CKH Dharan*
ABSTRACT
Natural composites of biological matter such as mycological fungi offer several
advantages, including freedom from oil feed-stocks, low cost production, carbon
capture and storage. These benefits make mycology materials carbon-neutral or
even carbon-negative. Composite materials remain the material of choice for a wide
variety of applications, but the high cost of raw materials and complex processing is
opening a new avenue for sustainable composites. The vegetative part of fungi,
called mycelium, provide a fast growing, safe and inert material as the matrix for a
new generation of natural composites, which can serve as replacements for
traditional polymeric materials for applications including insulation, packaging, and
sandwich panels. As seen in nature, natural foams can provide acceptable
mechanical properties, with the benefits of being lightweight, sustainable and inert.
In this investigation mechanical testing was conducted to determine the mechanical
behavior of a mycelium material, including its elastic and strength properties in
tension and compression. As in synthetic polymeric foams the mycelium material
exhibited a compressive strength almost three times the tensile strength. Its high
specific compressive strength made it a sustainable option as the core of sandwich
panels. The strength of the material was found to decrease with increasing moisture
content of the material, suggesting that coatings to inhibit moisture diffusion would
ensure consistency and performance.
2
BACKGROUND
Fungi occupy an unusual position in our world as having characteristics of both a
plant and animal and thus their own kingdom. Composed of vegetative matter the
structural part of fungi which forms its vegetative growth and mass is mycelium, a
eukaryotic cell encapsulated by a rigid cell wall. Mycelium is a network of carbonbased matter which grows as struts, forming the cellular structure of mycelium. The
mycelium network is made of individual hyphae, which grow from the inoculation
of a mycelium fungal strain spore into a cellular material, and consume carbon and
nitrogen containing feed-stocks to build a network of mycelium hyphae [1].
Unusually they are nonphotosynthetic organisms which absorb all their required
nutrients from their host feed-stock. Typically found buried within degrading and
rotting bio-matter including wood, leaf matter, flesh, or any other carbon-containing
matter, the mycelium structure of fungi is often hidden within the host matter and
only becomes visible when the fruiting stage is reached and fruiting bodies appear
on the surface to disperse spores. In this investigation only pre-fruiting stage
mycelium were used to prevent exposure to spores for safety.
Mycelium has a fast growth rate and will continue to grow without
limitation with sufficient nutrients - the largest known mycelium growth is in
eastern Oregon, covering over 2,400 acres and estimated at over 2,200 years old
[2]. The mycelium hyphae network is used to grow to move location and seek new
feed-stocks, uptake and transport nutrients, and to relay chemical signaling
mechanisms which govern the mycelium architecture, growth and all other
functions [3]. Growth and nutrient harvesting are achieved by the secretion of
digestive enzymes, dismantling macro-molecules into components then absorbed
using a diffusion gradient or by transport mechanisms. Unlike plant based matter
based on cellulose and contain rigid liglin, rigidity in fungi is achieved with chitin
composed of polysaccharides, which forms the skeletal structural of the fungi and
defines the mycelium cellular structure.
Mycelium are an important part of our ecosystem, and play a vital
role in the recycling of minerals and carbon and in the nitrogen-fixing cycle. Edible
mycelium fungi are farmed for human consumption, and are used in a broad range
of applications including environmental control with fungal biological control
agents [4], capture and safe removal of heavy metal contaminants [5], and even
medical uses fighting cancer [6]. As a biological material, mycelium presents an
attractive sustainable option replace synthetic packaging and as structural materials
with the addition of reinforcements. Current crude oil based polymeric materials are
not sustainable have damaging environmental impacts including non-renewable
resource consumption, toxic byproducts, and the resulting solid waste which is
largely disposed of in landfill, storing up problems for future generations [7].For
example the natural degradation of polystyrene foam is very low (less than one
percent per year) and results in chlorinated hydrocarbon and other toxic byproducts
to animals and aquatic life. Due to their high growth rates, non toxicity and
sustainability mycelium based materials are being explored for use in structural and
architectural applications, including using mycelium based building blocks for
avant-garde structures termed Mycotechure [8], shown in Figure 1, and has also
been proposed as a living architecture material for a prototype sustainable building
for recreation in Kunming, Southern China [9].
3
Figure 1. Mycotectural Alpha by Professor PG Ross
exhibited at Kunsthalle Düsseldorf as part of the Eat Art Exhibit 2009 [8]
Modelling Mycelium as an Open-Cell Foam
Out of the several thousand strains of naturally occurring mycelia, Ganoderma
lucidum, a commonly known edible strain, was selected to be grown for testing. In
this investigation this grown strain is henceforth referred to as the mycelium
material. The mycelium material discussed in this paper can be conceptualized as a
composite material composed of a mycelium foam matrix, with reinforcing short
wood fibers. Wood itself is a highly anisotropic closed-cell foam, thus the
composite‘s hierarchical nature. Based on previous micrographs of mycelium, G.
lucidum was expected to be an open-cell foam [10]. Previous studies of the
mechanical behavior of open-cell foams can be used to inform predictions of the
behavior of mycelium.
A foam is a three dimensional (3D) array of cells forming a cellular
solid, such as cork, polyurethane foam, or even bread. Open-cell specifies that the
cells have no cell walls, only beams forming cell edges. Liquids and gases can pass
more freely through an open-cell foam than a closed-cell, as is required for gas
exchange within biological organisms [11]. Foams behave differently in tension and
compression, and the stress-strain curve also varies depending on the solid material.
Figure 3 shows typical curves for compression and tension for three cellular
material types: elastomeric, elastic-plastic, and brittle. The compression curves all
show three distinct regions: linear elastic, plateau, and densification. The linearelastic region reflects elastic bending of the cell edges and stretching of cell walls
(if present). The plateau occurs as the cells begin to collapse, via either elastic
buckling (for elastomers), plastic yielding (for elastic-plastic materials), or crushing
4
(for brittle materials). Finally, once the cells have fully collapsed, the solid material
is compressed and the stiffness increases to fracture during the densification region
[11]. Tensile stress-strain behavior also begins with a linear-elastic region. For
elastomeric and elastic-plastic materials, the stiffness increases as the cell walls
become aligned. For elastic-plastic materials, the cell walls must yield first,
reflected in a brief plateau. In brittle foams, fracture occurs before the cell walls can
align. Some foams demonstrate brittle behavior in tension, but elastic-plastic
behavior in compression [11]. Deformation of the cubic strut structure occurs under
load as modeled in Figure 2.
While the mycelium material is considered open-celled for gaseous
exchange, it is biological in nature and may have non-uniform areas of closed-cell
architecture, suggesting local geometry of the cell walls may affect the mechanical
performance. However, previous research has shown that most open or closed cell
foams act as if open-celled, due to the negligible contribution to the overall stiffness
and strength from the thin cell wall faces [12]. Ashby, widely published in
describing the mechanical behavior of bending dominated cellular structures,
together with Gibson proposed Equation (1) to describe the properties of air filled
foams based on the elastic modulus at a specified density [13], where is modulus
of the mycelium foam material,
is the modulus of the mycelium hyphea, is the
density of the mycelium foam material and
is the density of the mycelium
hyphea.
2
(1)
Figure 2. Unit cell [11]: (a) for an open-cell foam of cubic symmetry, (b) for a closed-cell foam of
cubic symmetry, (c) shown after linear-elastic deflection (open-cell) [14]
5
Figure 3. Typical stress-strain behavior in foams [11]
Khazabi et al. found that wood fibers in a polyurethane spray foam were mostly
incorporated into the cell walls, due to compatibility between the wood and the
polymer. Wood fibers decreased overall shrinkage by increasing cell stiffness. Cells
became larger and more irregular with increasing fiber concentration, and the foam
became less homogeneous. Shorter fibers led to a higher number of cells with
decreased cell wall thickness. Increasing the proportion of wood fiber in the
polyurethane foam increased the compressive strength and decreased the tensile
strength. They attribute these results to both the stiffening of the cell walls, as fibers
are incorporated, as well as the mutilation of cell shape due to fiber interference.
These studies considered fibers up to 1.0 mm (slightly larger than the cell size) [15].
The mycelium composite studied here is expected to show a larger fiber to cell size
ratio. Previous studies of fiber-reinforced foams mention the importance of
adhesion between the fiber and the foam material. Considering that the fibers used
here double as a feedstock for mycelium, adhesion is expected to be strong and
consistent. In Holts‘s study of mycelium grown on cotton plant material, no clear
relationship was established between feedstock particle size and resulting
mechanical properties.
6
Current Mycelium Composites Applications
Mycology materials have only recently begun to be explored as an engineering
material, and thus far research into their mechanical properties has been very
limited. Mycelium is currently being commercially developed for packaging
materials, insulation, structural insulating panels, and acoustical tiles [10]. It is also
being explored for use in composite materials with carbon fiber or fiberglass. Some
of these applications avoid using adhesives, since mycelium naturally bonds to its
feedstock. Agricultural byproducts are used for the primary feedstock, and the
resulting material is compostable. The mycelium grows without light, water, or
petrochemicals [10]. Holt et al, one of the few major contributors to the field so far,
further describe material processing and properties, using a feedstock composed
primarily of cotton carpel (a waste part of cotton plants), along with smaller
proportions of cotton seed hulls, starch, and gypsum. Their study compares twelve
different growth methods, using six different ranges of particle size for the carpel,
from 0.1-51.0 mm, and two methods for inoculation via a liquid or a solid substrate.
They found the liquid substrate was easier to implement and also resulted in more
uniform delivery [16]. The feedstock blend is heated for sterilization, inoculated
with a G. lucidum fungus, packed into a mold, and sealed to create a uniform
environment. Mycelium growth occurs over five days at room temperature, after
which the material is held at a higher temperature to stop growth [16]. The study
measured shrinkage, density, flexural strength, elastic modulus, compressive
strength, aging degradation, water absorption, R-value (a measure of a materials
thermal resistance often used in the building and construction industry), thermal
conductivity, and fire behavior (via cone calorimeter testing), using primarily
American Society of Testing and Materials (ASTM) published testing standards.
Their results are summarized in Table I. Despite the mechanical properties showing
a very wide range, Holt et al. concluded that mycelium presents a practicable
alternative to polystyrene packaging foams [16].
METHODOLOGY
Testing were completed according to ASTM D3574 - 11 Standard Test Methods for
Flexible Cellular Materials—Slab, Bonded, and Molded Urethane Foams, normally
used for polyurethane foam. This standard provides the most applicable testing
methodologies for a natural material with a foam-like structure, as no testing
standards currently exist specifically for natural composite foams. The composition
of the material is a mix of the mycelium and the remaining feedstock of undigested
wood chips. The material, shown below in Figure 4, is formed as mycelium
decomposes organic matter. The network of hyphae penetrates the feedstock‘s
cells, using secretions of acids and enzymes, and converts the nutrients to
mycelium, growing the network of hyphae. Areas of pure mycelium growth (white)
can be seen within the material, and the surrounding external surface is composed
of a continuous layer of mycelium.
7
TABLE I. MATERIAL PROPERTIES OF MYCELIUM
GROWN FROM COTTON CARPEL FEEDSTOCK [adapted from [16]]
Density
(kg/m3)
Flexural
Strength*
(kPa)
66.5-224
7-26
*normalized to polystyrene density 32kg/m3
Elastic
Modulus*
(kPa)
123-675
Compressive
Strength*
(kPa)
1-72
Figure 4. Photograph of mycelium block as grown
Figure 5. Summarized production process of mycelium material
Currently there is no established method to determine the ratio of fibrous mycelium
matter to wood chip feedstock matter in mycological composites. Several methods
to estimate the relative composition fraction of wood and mycelium were
considered, including estimation by analysis of SEM image or visual inspection, but
neither method was developed further or tested for accuracy. Analogous to the fiber
volume fraction of fiber reinforced polymeric composites the average density of the
mycelium material was calculated. If considered as a composite material, with the
8
remaining wood chip as clusters of fiber reinforcements and the grown mycelium as
the matrix, an estimation of the composite density could be made using the rule of
mixtures. Since the mass fractions of fiber and matrix cannot be found from the raw
materials (due to the conversion of the carbon-containing cellulose into carboncontaining cellular structures), the composite density could only be calculated by
estimating the wood fiber and mycelium matrix volume fractions.
Growth and fabrication of mycelium specimens
The isolated strain, G. lucidum, was inoculated into molds containing the feedstock
material including macerated Quercus kelloggii (Red Oak) wood, macerated into
5.0-15.0 mm chips, and a nutrient solution. Growth occurs under controlled
conditions. Pending IP prevents full disclosure of the nutrient solution and growth
conditions. Once the required degree of conversion of feed stocks to mycelium biomatter is reached, the growth process is halted by denaturing with heat treatment, at
220oC for 120 minutes. Post-processing includes the reduction of moisture content
from 60-65% to 10-20%, via convective heating using solar dryers or renewable
energy sources to minimize the energy content of the drying process, indicated by
life cycle cost analysis, not reported here, to be a small constituent of the material‘s
total life cycle energy input. The production process of the mycelium block is
summarized in Figure 5. The mycelium was grown into simple rectangular block
molds for fabrication into test specimens. Once the mycelium comes into contact
with non-porous, inorganic materials, a hard chitin skin is formed, to prevent
moisture and nutrient loss. Chitin is also found in nature as the armored exoskeleton
of beetles and other arthropoda. The blocks were denatured before the chitin skin
had formed, when the skin had not fully developed a rigid, chitin rich composition
(as seen in the scanning electron microcopy (SEM) images of the surface).
Samples were cut into test specimens using a General Electric
vertical bandsaw at 1725 rpm. This proved difficult due to the frangible structure of
the dried material, and considerable debris was produced during cutting. During test
specimen fabrication, it was noted the material was brittle and frangible, fracture
occurring at the boundaries between areas of mycelium growth and undigested
wood chips, implying a weak bond. Compressive and tensile specimens were
fabricated according to ASTM D3574, although some adaptations had to be made
due to the frangibility of the material. The tensile samples ‗dogbone‘ shoulder radii
was replaced with a chamfer to aid in fabrication, and the resin-glued metal tabs
with a 8mm diameter centered blind hole were extended beyond the sample, to
enable fitment into a pin-clamp as standard crush-jaw clamps would damage the
specimens.
Mechanical Testing
Tensile and compressive tests were conducted to determine the mechanical
behavior of the mycelium material under static tensile and compressive loads.
Tensile and compressive tests were carried out according to ASTM D3574, chosen
as the most appropriate standard for testing mycological composites.
9
TABLE II. TEST SPECIMEN MASS, DIMENSIONS AND MOISTURE CONTENT
Tensile
Compressive
Mass
(g)
40.9
40.7
Dimensions
Moisture Content
(mm)
(%)
25.2 x 25.7 x 141.1
5.7
55.1 x 55.4 x 41.9
5.8
Microscopy
Several images were taken using a scanning electron microscope (SEM) and an
optical microscope, to ascertain if there is a variation in cell structure or growth
direction, as seen in many other plant and animal cells. Optical microscopy was
carried out on samples from the longitudinal and transverse directions of the
mycelium block, at 3.9X and 7.8X magnification. Specimens of 25.4mm (1‖) cubes
were cold-mounted in resin and polished for optical microscopy. Sample imaging
was also completed using an SEM. These images allow us to examine differences in
the wood-mycelium composition throughout the sample and also to examine the
cellular structure of the mycelium and the wood separately. Five samples were
taken from different locations in a block, and multiple images at a range of
magnifications were captured for each. A Leo 430 SEM was used at a setting of 5.0
kV and 30.0pA. The samples were coated with a gold-palladium to prevent
charging.
RESULTS
Mechanical Testing Results
Mass, dimensions and moisture content were recorded for each specimen, and the
average determined for subsequent use in calculations, summarized in Table II. Due
to the mycology material being desiccated, the moisture content of the material is
~6%, which is less than 10% of the surrounding environmental humidity and thus
the material is mildly affected by the surrounding environments moisture content,
including air humidity. Thus the moisture content was recorded at the time of
testing using a digital resistivity moisture meter with an accuracy of 1%. Of the
three tensile and three compressive tests planned, all six tests were completed
successfully. Load deflection plots of the materials response to tensile and
compressive loads were recorded during each test, averaged, and the stress-strain
curves plotted.
TENSILE RESPONSE STRESS-STRAIN RESPONSE
The stress-strain response in Figure 6 of the material under a tensile load was seen
to follow the expected pattern for an elastic-plastic material: a linear-elastic region
up to a 0.2% offset yield point of 176kPa, a negligible plateau region, and finally
plastic deformation until brittle fracture at 15kPa. The stiffness (Young‘s Modulus)
of the material in tension, calculated from the elastic extension portion of the graph
was found to be 1.3MPa. The relatively low Ultimate Tensile Strength (UTS) of
10
15kPa reflects the brittle and frangible nature of the material. While relatively low,
for current applications the material will not be subject to tensile loading. However,
additional reinforcements and consolidation may improve the tensile properties, if
necessary.
Figure 6. Tensile stress-strain response
Figure 7. Compressive stress-strain response
11
Figure 8. Yield point of compressive stress-strain response
COMPRESSIVE RESPONSE STRESS STRAIN RESPONSE
The compressive test curve Figure 7 includes the three regions of linear elasticity,
plateau and densification. At very low strains (~≤5%) the materials response is
linear elastic, where the gradient equates to the Young‘s Modulus of the mycelium
material. As expected for a foam matrix, deformation was followed by crushing of
the foam cells, in this case the struts of the mycelium hyphae architecture, with
densification seen as a sharp increase of stress to strain. As load increases, the struts
of the cell walls begin to collapse. The collapse of the cells, and thus material,
continues approximately constantly until the opposing cell walls meet, causing the
stress response to increase sharply, identified as densification [12], [17]. The
material stiffness in compression was calculated as 1.0MPa, using the elastic,
proportional region of the graph in Figure 8 prior to the compressive yield at
47.5kPa. The ultimate compressive strength of 490kPa proved considerably higher
than the UTS.
MECHANICAL STRENGTH TO RELATION TO MOISTURE CONTENT
The ultimate material strength for the tensile and compressive samples were plotted
against the level of moisture content. The results plotted in Figure 9 suggest a
negative correlation between material strength and moisture content. As the
moisture content of the material increase, the mechanical performance of the
material under both tensile and compressive loads decrease, signifying the
plasticizing effect of moisture, a common characteristic of plant materials due to the
polar water molecules adhering to polymer molecules and promoting dislocation.
12
Figure 9. Material strength in relation to moisture content
Optical Microscopy Results
The optical microscopy images, Figure 10, taken in the longitudinal (a), and
transverse (b) directions of the mycology blocks do not show any obvious growth
orientation of the mycelium material. This is consistent with the previously
identified cellular structure of mycelium as non-directional tetrahedrally-connected
struts [11]. The images show clusters of undigested wood feedstock, with clearly
identifiable longitudinal wood cells. An image (c) of an un-mounted specimen at
the same location as this better shows the white fibrous interior mycelial growth
around the wood feedstock. Similar studies have found wood fiber reinforcements
have an impact on elastic and mechanical properties of the resulting composite.
Elastic properties typically increase with hardwoods, such as Red Oak feedstock
used here, and also with defibration (the separation of fibers from one another),
when macerated into wood chips [18].
13
Figure 10. Resin-mounted optical microscopy images: (a) Unmounted transverse image at 4X
(b) Unmounted longitudinal image at 4X (c) Resin mounted transverse image 8X
(d) Resin mounted longitudinal image at 8X
Figure 11. Locations of material sampling from block for SEM images: (1) Interior mixed
(2) Top surface (3) Interior pure mycelium (4) Interior pure wood chip (5) Bottom surface
Scanning Electron Microscopy Results
Samples were cut from a single mycelium-wood block, from five different
locations: the center (sample 1), the top surface (sample 2), the bottom surface
(sample 5), a cluster of pure mycelium from just under the surface (sample 3), and
of an individual wood chip (sample 4), as shown in Figure 11. The images show
extreme heterogeneity at all scales, with a randomly oriented mix of mycelium and
woodchips. The image of the full block in Figure 4 shows a fully white myceliumcoated surface. The amount of mycelium decreases towards the center, which
appears to be purely wood. The section just under the surface was selected because
14
mycelial growth was thickest. The image in Figure 12 (b) shows a mass of tangled
hyphae, originally growing in biological fluid mostly comprised of water, and
shown in the image as suspended in air once the material has been desiccated,
forming a structure more similar to a fibrous mat than to easily delineated cells. Top
and bottom surfaces show the self-skinning property of mycelium, with a thinner
solid face grown between the individual hypha in Figure 13 (a).
Figure 12. Pure mycelium (sample 3) SEM magnification of (a) 36X (b) 2000X
Figure 13. (a) Top surface (sample 2) SEM magnification of 3800X
(b) Bottom surface (sample 5) SEM magnification of 750X
Figure 14. Interior center (sample 1) SEM magnification of (a) 750X (b) 8000X
15
Figure 15. Pure wood chip (sample 4) SEM magnification of 750X
Figure 16. Hyphae density variation at different locations: (a) Bottom surface (sample 5) SEM
magnification of 3800X and (b) Interior (sample 1) SEM magnification of 8000X
SEM images from the center sample show mycelial growth not visible to the naked
eye, forming a network of hyphae in Figure 14. The image in Figure 15 shows the
wood-mycelium interface. However, the individual wood chip picked out from the
block does not show any obvious mycelium, and the longitudinal cellular structure
of the wood has remained undigested, causing the frangible natural of the material.
The diameter of the hyphae struts was calculated from the images, all showing
hyphae diameter within the range 0.5-1.0µm. The density of the hyphae, in Figure
16, showed extreme variation between surface and interior locations, with the
interior (d) showing less hyphal density than surface locations (a) and (c). Previous
work imaging mycelium has demonstrated a tetrahedral cell structure [2]. The
random mat structure observed in these SEM images of G. lucidum may transform
into a more regular, repeating tetrahedral cellular structure, as the proportion of
mycelium material to feedstock material increases with further growth.
16
TABLE III. COMPARATIVE MATERIAL PROPERTIES [adapted from [19], [20], [21], [22], [23]
Material
Modulus,
Density,
E/ρ
Yield
Ultimate
Syc / ρ
Sutc /
E
ρ
Strength,
Strength,
ρ
(MPa)
(kg/m3)
Syc
Sutc
(MPa)
(MPa)
Present
1.30
318
0.004
0.0475
0.49
0.0001 0.002
Investigation
G. lucidum
Starch based
183
260
0.704
1.18
1.09
0.005
0.004
foam (w/
fiber)
Polystyrene
5.70
41.2
0.138
0.179
0.004
foam
Polyvinyl3.00
50
0.06
45.0
0.900
chloride foam
Aluminum
347
255
1.40
1.69
0.0066
Foam
CONCLUSIONS
The mycelium material was seen to be a composite material of mycelium foam
matrix and wood reinforcement. No growth orientation was found, and SEM
images confirmed that the mycelium matrix formed around the wood chip regions,
forming a network of hyphae that shows increasing density towards the selfskinning exterior of the material. Static mechanical tests showed the frangible
nature of the material resulted in a low material ultimate tensile strength of 15kPa,
with a tensile modulus of 1.3MPa, indicating high stiffness. In compression the
material demonstrated a yield point of 47.5kPa and ultimate compressive strength
of 490kPa. The strength of the material was found to decrease with increasing
moisture content of the material, thus the moisture content reduction process is vital
to ensure consistency and performance.
The predicted modulus of the mycelium foam material was
calculated using Equation (1) [13], with the density of dried mycelium as 1400
kg/m3 and modulus of the mycelium theorized as 20MPa [24], predicting the
modulus of the mycelium foam material as 1.03MPa and the experimental
measured modulus was 1.3MPa. The difference between the predicted and
experimentally measured modulus implies the density and modulus of the
undigested wood chips present in the mycelium material should be accounted for. If
considered as a composite material, with the remaining wood chip as clusters of
fiber reinforcements and the grown mycelium as the matrix, an estimation of the
composite density could be made using the rule of mixtures. Since the mass
fractions of fiber and matrix cannot be found from the raw materials (due to the
conversion of the carbon-containing cellulose into carbon-containing cellular
structures), the composite density could only be calculated by estimating the wood
fiber and mycelium matrix volume fractions. Currently there is no established
method to determine the ratio of fibrous mycelium matter to wood chip feedstock
matter in natural composites, analogous to the fiber volume fraction of fiber
reinforced polymeric composites. Several methods to estimate the relative
17
composition fraction of wood and mycelium were considered, including estimation
by analysis of SEM image or visual inspection, but neither method was developed
further or tested for accuracy.
When compared to commonly used polymer foam materials as
summarized in Table III, the mycelium material had an average density and
strength comparable to polymer foams, indicating properties closest to Polystyrene
expanded foam. While the mycelium material is not comparable to the mechanical
performance of a metal foam, the material has the advantages of being a naturally
occurring, sustainably produced and free from toxic manufacturing process
including toxic foaming agents. Mycelium materials can be grown in large volumes
from waste feed-stocks such as corn husks, wood chips or cotton carpels [16],
without the need for costly manufacturing processes and offering improved
environmental safety, indicates potential as a replacement for current polymeric
foams used in insulation, packaging, and sandwich panels.
While frangible overall the material demonstrated robustness, which
could be improved by control of the feed-stocks, mycelium strain and the inclusion
of natural additives to promote bond strength between the mycelium and feed-stock,
analogous of the sizing for fibers used in polymeric composites. The dynamic
properties of the mycelium material would prove a vital part of future efforts to
fully characterize its mechanical behavior, including for mechanical and acoustic
vibrations, as a variety of applications exist for sustainable materials that have
damping properties. Internal and panel reinforcements may provide a way to
increase stiffness and strength of the mycelium material, suggesting a multitude of
novel sustainable sandwich composites that remain to be explored. Prior to
denaturing, individual live blocks of mycelium can be combined to produce a single
continuous block. Complex 3D physical shapes can be created from combining
multiple blocks of mycelium in its growth stage, producing variable section
architectures and reinforcements without requiring any cutting processes or waste,
providing near net shape manufacturing. By placing blocks in close physical
contact, the skin is absorbed into the mycelium overall cellular structure, creating a
single block. With future work, a testing method could be developed to determine
the bonding strength and mechanical behavior of combined mycelium materials.
This has a multitude of applications as blocks can be combined to produce any
architecture required, including complex 3D shapes. Carbon-neutral sandwich
composites could be created using the sustainable mycelium material as a foam core
with fiber-reinforced panel skins (ideally likewise sustainably made of eco-resins
and natural fibers). Laminate panels can be adhered or permanently attached to the
mycelium blocks, creating a sandwich panel, similar to bamboo laminate panels
combined with a polymer foam core.
Currently mycelium materials inhibit decay in the end-use
environment by desiccation, preventing re-activation of mycelium growth by
maintaining less than 10% of environmental humidity. This may require external
coatings to maintain low moisture content, to mimic the impermeable chitin skin
formed in the later stages of mycelium growth which itself could be controlled to
produce a natural coating without the need for coating processes. Entirely
comprised of natural materials and thus edible, mycelium materials are susceptible
to consumption by vermin such as insects and rodents, and competing fungi species,
which non toxic natural compounds found in edible essential oils may provide
18
antibacterial and antifungal protection from [25], an improvement to currently used
toxic antibacterial and antifungal chemicals. During growth the elimination of
competing fungal species is vital to ensure the growth of the selected inoculated
fugal strain, requiring clean room preparation as the feed-stocks provide nutrition
for any fungi introduced, including competing species. This could also be exploited
to produce hybrid mycelium strains, exploiting the differing mechanical properties
of different strains to produce tailor-made material properties. Mycological
materials are entirely compostable, degrading into its natural constitutes producing
soil humus, while aiding the nitrogen-fixation process of soils. In comparison to
polymeric materials the fast decay time and natural decomposition of mycelium
materials provides reduced environmental impact.
In summary, mycological natural composites have great potential for
a scaled manufacturing process, with low feedstock and process costs, carbon
neutrality, and the ability to be easily combined with hierarchical structure
reinforcements and growth-controlling processes. While the material could be
improved to provide greater mechanical performance, the mycelium material boasts
novel sustainable qualities and properties that may make it competitive as a
structural engineering material in certain applications. The material exhibits
promising mechanical properties with a view to replacing similar oil-derived
materials, at a fraction of the cost and reduced impact on the environment. With
relatively small investment in additional internal architecture and fine control of the
biological processes in a clean room environment to ensure purity when scaling up
such a production process, a multitude of new combinations of materials are
possible, with applications ranging from furniture to aerospace composites.
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