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OPEN FUNG INTRODUCTION:
In 2015 Hannah Nguyen conducted foundational research on fungal composite materials in aquatic environments while she was an undergraduate at UC Berkeley. At that time, Hannah was a student of the renowned mycologist Tom Bruns. She then joined the company MycoWorks to conduct capstone work to test fungal materials in the diverse fresh and marine waters of California’s Bay Area. Hannah grew a “myco-buoy” with the same form factor as a standard Styrofoam buoy used in commercial applications, sealed them with different organic coatings, and placed them in different conditions to see how they fared.The following is Hannah’s honor's research project for her major, Conservation and Resource Studies, through the College of Natural Resources and the Plant and Microbial Biology Departments at UC Berkeley. It has not been peer-reviewed or published previously. We are sharing it so that this work on fungal buoys can help others working with fungi and water.
Maritime Testing and Degradation of Mycelium Composite Materials: The Ganoderma lucidum Buoy
by Hannah J. Nguyen
University of California Berkeley
Originally Published: May 2016
Re-Published by Open Fung: March 2025
ABSTRACT
Mycelium, the filamentous vegetative structure of a fungus, possesses dynamic capabilities that inspire biotechnologies encompassing the goal of sustainability by means of material efficiency. The demand for replacing excessively wasteful, energy-intensive building materials is gaining urgency, and mycelium composites present great potential for supplanting current material regimes. However, present information on how the material withstands weathering is limited. This experiment and subsequent analysis was conducted in the hopes of furthering application possibilities for mycelium objects and to better understand the degradation process of these composites. A set of buoys were grown out of mycelium from the species G. lucidum and set in the the San Francisco Bay. This method exposes the subjects to an extreme form of natural weathering. Two biodegradable sealants, shellac and natural latex, were coated on the buoys, and compared to a control group lacking any sealants. Water absorbency and buoyancy were then calculated and compared over the time of water and weathering treatment. A scale assessing changes in appearances was created using erosion characteristics defined in the standard ASTM C488-05. These optical assessments were recorded by taking photographs and notes of each buoy for every visit to the site. Finally, mechanical testing for hardness was taken for each type of buoy using a durometer in accordance with the standardized testing method ASTM D2240. The outcome of this experiment shows a positive potential for mycelium composite materials for both outdoor objects and maritime applications.
INTRODUCTION
As materials scientists and engineers explore alternatives to toxic and energy-intensive building materials, natural composite materials are gradually gaining attention. Wood fiber composites and foams often require polymers derived from petrochemicals, while treated wood requires an array of preservatives such as arsenic [13]. Many conventional materials such as these rely on resource extraction and processing, while the product’s chemical compounds are often harmful to humans. After usage, most petrochemically derived and treated materials are destined to slowly decay in landfills. In response, the natural material movement aims to create innovative, biomimetic, closed-loop systems for the design of products with extraction, manufacturing, use, and disposal in mind. Fungi perform an indispensable diversity of functions in the natural environment; and the mycelium of particular species can play an instrumental role in replacing many highly processed materials. Mycelium are the subterranean ‘roots’ and structures of fungi that reproduce via fruiting bodies. These fruiting bodies are the ‘dispersal phase’ of fungi and are recognized as mushrooms.
The 8,000 identified saprophytic macrofungi are particularly appealing for alternative materials, as they decompose decaying organic material by recycling carbon, nitrogen, phosphorous, and other essential elements [7]. This feature enables the mycelium to take the shape of a chamber containing a feedstock. The feedstock can be any organic matter. This is advantageous in that it implies saprophytic fungi can be grown on the mass amount of biowaste disposed of every year to create usable, compostable objects.
Mycelium materials express traits that facilitate an abundance of possibilities for uses and products. The applications for this material are versatile because the density, consistency, and elasticity are determinant on the the variations of growth processes, species, and substrates. Developing research for mycelium material applications include thermal insulation, sandwich composites for furniture components and building structures, styrofoam substitutes, and biopolymer foams. Though versatile in characteristics, the mycelium material is consistently buoyant. This trait allows for exploration into maritime applications such as flotation devices or oyster restoration beds.
Little research has been conceived on the subject of outdoor degradation for the mycelium composites. Similar to wood, eventual decay in an outdoor environment without preservatives and treatment is inevitable. However, with the use of natural sealants, the mycelium material may withstand weathering and water decay without compromising its compostability. This experiment seeks to better understand the degradation process of the material while furthering possibilities for outdoor applications by comparing natural sealants. This was achieved by growing mycelium in the shape of buoys, painting them with natural coatings, and setting them in the San Francisco Bay for 40 days for investigation and analysis.
This methodology for weathering was chosen in order to contrive data and observations from a natural environment where mycelium composites could likely be applicable. This experiment investigates how the material physically degrades, how long it stays afloat in water, which sealant most effectively inhibits water infiltration, and what its physical property of hardness is. Ultimately, this research exposes further possibilities for functions of natural composites made of mycelium and biowaste.
METHODOLOGY
Species
Ganoderma lucidum, also known as the Reishi or Lingzhi mushroom, was chosen for this experiment for its resilience, rapid growth, and appetite for carbon-containing organic matter. Ganoderma is a genus of polypore mushrooms known for breaking down lignin and cellulose [9]. Recognized as a medicinal mushroom for over 2,000 years, G. lucidum contains roughly 400 bioactive compounds including triterpenoids and polysaccharides[7]. The mushroom is sold commercially in the form of tea and food supplements for its many health benefits [12]. This genus is currently being researched for its potential use in bioremediation as it is able to break down contaminants[7].Mycelium Material Explained through Microscopy
First, microscopic pictures were taken of a mycelium composite sample in order to analyze the structures of hyphae and feedstock. Figure 1 shows fungal cells consuming a substrate (wood particle) by means of extracellular digestion. Mycelium is considered to be an ‘opened-cell’ foam because the hyphal structures are distributed as a large web, rather than a collection of walls (as a soap film) [1]. In ‘opened-cell’ materials, water and gas are able to flow more easily through the structure than ‘closed-cell’ foams [9]. Wood is deemed as a ‘closed-cell’ foam, because its cellular structure takes the form of small plates that form the sides and faces of the cell [1]. The mycelium is isotropic , growing in all directions, while the structural properties of wood are regarded as orthotropic (having three planes or axes of symmetry) and anisotropic (directionally dependent) [1]. The mycelium intermixed with substrate can be characterized as a composite material of a ‘fungal foam matrix with a wood reinforcement’ [9].Figure 1. The above images were taken with an Scanning Electron Microscope (SEM) imaging system using a small sample of the material before water treatment. The capillaceous hyphal structures are intermingled and permeating through a wood fiber particle. Image a is 4x more magnified than the image b. The left-hand side of both images show the wood particle’s anisotropic structure in contrast to the mycelium’s isotropic arrangement seen on the right sides of the photographs.
Figure 2. This SEM image displays the magnified mycelium as individual growing hyphae strands that form the vegetative structure of the fungi. Together these hyphae constitute networks called mycelium that relay chemical signals, dictate the growth, movement, nutrient uptake, and all other functions of the fungi.
Since the ratio of mycelium to substrate is dependent on both the duration of growth time and aeration, layers of differing densities form in the growth process of thick molds and can be halted and analyzed, as shown in Figure 3c below. The ratio of mycelium to small, reinforcing wood and substrate pieces can better be conceptualized with the imagery. Image (c) displays the layers of differing densities and growth stages of the mycelium on the substrate. The smooth section at the bottom of the sample in image ( c) is the ‘skin’ portion, which corresponds to the the most mature growth stage. At this point, the mycelium has digested all of the substrate. In the absence of heat sterilization, fruiting bodies will eventually materialize from this portion.
Figure 3. The above images a,b,c,and d are magnified images of the same cross-section sample of mycelium material in different magnifications and angles. The white portions of the photos are the mycelium, and the darker portions undigested agricultural and wood by-product particles.
The mycelia is capable of self-recognition, meaning as it grows multi-directionally and digests its substrate, hyphae strands identify each other and bond to one another forming ‘clamp connections’ [7]. These bonds reinforce the structure and are the basis of the structure’s growth.
This unique growth technique offers an interesting advantage in working with the material.
Before the drying and heating phase of material manufacturing, if pieces of the object break, are uneven, have holes, or are cracked, one can simply place more substrate in the broken area or press pieces of the material together, allowing hyphae to clamp to one another, mending the broken pieces of the mycelium object.
Growth Parameters, Molds, and Methods
The growth determinants are primarily dictated by the typology and amount of substrate, nutrients in the feedstock, temperature, light, pH, water activity, and aeration [8].The initial growth of the mycelium for this experiment occurred in growth bags containing the inoculated spores of the species Ganoderma lucidum on a substrate composed of agricultural and wood by-products. These growth bags are sealed; however the membrane contains a small patch that acts as a filter to both enable the essential exchange of oxygen and carbon dioxide for the organism’s respiration, and to inhibit the introduction of competitive fungi and bacteria [7]. As the mycelium digests the substrate, a thick ‘skin’ layer forms around the perimeter of the inside of the growth bag. This tough mycelium ‘skin’ is made primarily of chitin, and helps to prevent nutrient and water loss [9]. The presence of the skin indicates that the substrate is colonized and preparing to produce their reproductive structures--mushrooms.In order to create objects out of the mycelium, the colonized material is cast into a specific mold in order to obtain a desired shape. The process of placing the mycelium and substrate material from the growth bag into a mold requires a clean environment, as it is susceptible to infection. Handling the material requires gloves sprayed with alcohol and disinfected surfaces. For further disinfection, a spray consisting of lemon, water, and antibacterial essential oils was generously sprayed directly on the material and on objects in contact with it. Throughout the process of growth and exposure to the atmosphere, this disinfecting procedure is repeated. The intermittent spraying of this mixture provides a desired equilibrium of moisture content for growth.
The molding containers used to grow the mycelium buoys into a cylindrical shape were ½ gallon buckets lined with large zip-lock bags. Before filling the lined containers, the mycelium, woody matter, and skin layer from the growth bag were broken apart by gloved hands and a blending apparatus. The mixture was then densely packed into the lined ½ gallon bucket.
The lining bag is then partially zipped, allowing for gas exchange, and kept in a semi-sterile room at 73o F. The room hosts a monitoring air filter device, and any objects or humans passing through are carefully cleaned. It is important to keep competitive fungi and bacteria away from the exposed, blended material as a precautionary measure as it may be susceptible to infection. The most common infection for this species at this state is Penicillium digitatum, commonly known as ‘green mold’.
The mycelium buoys were left in this controlled room for roughly 30 days, being sprayed and rotated weekly. After the first week, the bucket mold and plastic interlining were separated. The bags were cinched away from the cylindrical growing mycelium to enable the sides of the structure to more rapidly grow by exposure to the atmosphere. One week after being packed into the mold, all the mycelium buoys had a recorded average moisture content of 40% and each weighed on average 63.77 oz. The second week, the infantile buoys were taken out of the bags and placed in a larger container box with a lid slightly ajar for aeration.
During the third week, they were cored by forcing a 1” in diameter, toothed PVC pipe through the center with a mallet. Once hollowed through the center, they were left for one more week of growth before drying. The remaining material is a mixture of both mycelium and undigested wood flour substrate. Just as the mycelium formed a layer of skin around the perimeter of the inside of the growth bag, a layer had formed around the outer faces of the buoys. This results in a difference in density and mycelium-substrate ratio from the center of the object, in comparison to the exterior faces.
Figure 1. Ganoderma lucidum and its substrate in cylindrical molds in a controlled environment. Packing the material into the mold at a high, homogenous density gives the product a consistent structural integrity.
Figure 2. One week of growth in the molding container. The material is taken out of the mold container and the bags are cinched away from the sides to allow for aeration to expedite growth.
Figure 3. Each mold was taken out of the individual bags and put in a large container left slightly ajar, allowing for continuous atmospheric contact. Thick mycelium ‘skin’ layer formed around the exterior of each piece. The ‘skin’ at this growth stage is easily compressible and takes on a spongy consistency. Though the mycelium holds a more apparently dominating presence, it is still susceptible to green mold infections, and therefore is kept in a clean environment and sprayed with the lemon, water, and antibacterial essential oil mix. This photo was taken after one week of being moved into the larger container; accounting for three weeks of total growth.
Figure 4. Fourth week of growth. Buoys were rotated out of the holding container and into shelving, as there is less of a chance of infection at this stage. Pieces showing signs of green mold were isolated in a separate bag.
Figure 5. Each buoy was hollowed using a cylindrical 1” toothed pipe and a mallet.
Drying
For optimum drying, the samples were taken out of the growing room and placed on drying racks (at room temperature) in preparation for heating. To effectively halt the growth of mycelium, all mycelium buoys were heated in a conventional oven to reach an internal temperature of 150o F. Heat sterilization at this temperature, before the fruiting phase of growth, denatures their spatial arrangements and ruptures protein subunits [8]. It is important to stop the growth of mycelium before the hymenium layer forms to prevent the production of spores. Avoiding spore production inhibits the possibility of infecting and digesting lumber or other carbon-containing material that it may come in contact with [8]. It is additionally a safety precaution in that fungal spores may affect human’s respiratory health [8].After heat treatment, all the buoys had an average of 13% moisture content as read from a hydrometer. From such a loss of moisture, they had lost 10% of their volume. Each weighed an average of 21.56 oz., retaining 35% of their initial weight (ave. 61.64 oz). This 35% weight retention does not include the weight of the hollowed central pieces, as the initial weight was recorded before the coring of the material.
Figure 6. The growth and heating process is complete, and the above images illustrate the buoys on drying racks.
The mycelium buoys are prepared for sealant coatings and water immersion.
Sealants
The two sealants used for the experiment were amber flake shellac and liquid natural latex. These sealants were chosen based on their hydrophobic qualities, accessibility, innocuousness, and ability to break down in a non-polluting manner. Both of these coatings are compostable, thus making the entire buoy a compostable item. Shellac comes from the insect Kerria lacca, a species of scale insect that feeds on tree sap. It is a combination of the insect’s shell and the resinous ‘lac’ that it excretes. It comes in a flake form and is mixed with ethanol in order to easily be painted on. It is popularly used as a colorant, for wood finishes, and food glazes [2].Natural latex is different from synthetic latex in that it is derived from the rubber tree instead of petrochemicals. ‘Latex’ will hereafter refer to natural latex, and not synthetic latex. The latex coating consists of ⅔ part water, ⅓ pure latex extracted from the Hevea brasiliensis rubber tree, and 1.6% ammonia for preservation and pH control. The ammonia is evaporated upon exposure to the atmosphere.
Latex in its raw form is a milky sap substance that over 20,000 species of plants from over 40 families (both monocotyledons and dicotyledons, and some members of the fungal kingdom) contain. This complex emulsion coagulates upon exposure to air, and is used as a defense mechanism against herbivorous insects and animals [5]. Though many species produce latex, around 12,000 species produce latex containing rubber, and of those, only some are specifically chosen for commercial use. The degradation rate of latex is known to be affected by light intensity and the polymer’s thickness [5]. Research conducted on latex in a simulated environment to test degradation processes by singular mechanisms such as photodegradation, biodegradation using microbial cultures, and thermal degradation compartmentalizes our understanding of the decomposition of latex [5]. There is little comprehension as to how these processes affect the material all at once at a micro-level, as it would in real environmental conditions.
Two coats of the amber shellac were carefully, and as evenly as possible, hand-painted on half of the buoys, including the inner-cored walls. The latter half of the buoys were painted with two coats of liquid natural latex. Both sealants dried in nearly 30 minutes.
Figure 7. Mycelium buoys with two coats of shellac.
Figure 8. Shellac-covered individuals are propped up to evenly dry while romantically taking in the evening sky and cityscape.
Figure 9. Mycelium buoy in the process of being covered with liquid natural latex.
Figure 10. Drying process of liquid latex. The latex in liquid form is milky white but dries clear. The three pieces pictured were covered one after the other; the far right piece showing the most recently coated.
Deployment Apparatus Design Method and Site
Five shellac-covered, five latex-covered, and two control buoys with no sealants were fastened to the side of a boat in Sausalito, CA . Here they were able to experience tidal shifts and weathering in the extreme form of idly bobbing in the San Francisco Bay. They were strung together with rope, and a 10” hose was inserted like a collet with a knot at either end to limit the amount of friction between the rope and inner core. The average salinity level at the site is 25.8 psu (practical salinity units), and the average temperature of the water is 58o F [6]. The buoys were left there for a total of 40 days. They were briefly removed after the first ten days and the 40th day for individual buoyancy tests, weight recordings, and optical assessments of degradation. Figure 11. Mycelium buoys in Sausalito, CA.
Figure 12. Apparatus design of latex, shellac, and controls. Photograph was taken after 10 days of water treatment.
DEGRADATION & MECHANICAL TESTING METHODOLOGY
Buoyancy and Water Absorbency
Buoyancy testing was conducted on the specimens intermittently throughout the 40-day period of immersion. Each buoy was tested before water immersion, 10 days after immersion, and 39h days into immersion, at which point they were removed from the water. The Buoyant Force, or the weight of displaced water, was calculated by first measuring the volume of displaced water in a bucket. The ½ gallon bucket was filled to 64 oz, and the risen level of water when each buoy was immersed was recorded. The volume of the displaced water is the difference in the measurement of the immersed buoy and the initial measurement of water. Next, the weight of the displaced water was calculated by using the formula Density= Mass/Volume, in order to obtain the mass. The density of the water as a function of salinity was found using the average water salinity in Marin (25.8 psu) and average surface temperature (58o F) to give a density of 1.0189 g/cm3 [5,9]. Once the density was known, the volume of displaced water for each buoy was plugged into the density equation to find the mass of displaced water. Once mass was calculated, the equation Weight= Mass x Gravity (g=9.8N/kg) was used to find the weight of the water displaced. The Buoyant Force was then recorded in Newtons (N). The buoyant force increases as mass, in relation to water absorbency, increases. This is an important factor in indicating how long the buoys are functional and afloat.Comparative analysis of the volume of water displacement to water absorbency as a function of mass can help to find an ideal equilibrium for floatation. Water absorbency in relation to the water resistance of each sample type is representative of the material’s ability to withstand water inflation and an indicator of water resistance over time. The buoyant force calculation is proportional to the mass of the object, and can be used for further water applications such as oyster restoration beds, floatation devices, and large-scale maritime products. Water absorbency was analyzed by comparing individual weights before, intermittently, and after water treatment and were recorded on site at the same time intervals as the buoyancy tests in order to accurately compare results. Though the weight could be determined by the water displacement test, it was also determined using a scale for accuracy.
Optical Assessments
The ASTM C488-05 (2010) Standard Test Method for Conducting Exterior Exposure Tests of Finishes for Thermal Insulation was applied in optically assessing the degradation of the subjects over time. Applying this standard as a method for optical assessment is appropriate as the material has previously been studied for its thermal insulation properties, and because the degradation of the finishes is a key factor in the degradation of the material itself.Photographs of each side of each buoy were taken prior to water immersion, and photographs and notes on degradation levels were taken during each visit to the site. Observations were contrived by comparing these photographs and notes. The issue with optically assessing the material is that the methods are vulnerable to subjectivity and difficult to quantify. However, in an effort to qualitatively assess the degradation process of the material, it is imperative to describe the visual changes in appearance of the subjects. Terminology relating to the material and finishes under evaluation are as follows:
- Discoloration-- color fade or change
- Cracking-- a line on the surface of something along which it has split without breaking into smaller parts
- Crazing-- network of fine cracks on surface
- Flaking--to fall away from a surface in thin pieces
- Chalking--‘powdering’, may give appearance to color fading
- Blistering--form swelling filled with air or fluid on surface
- Holes--opening or depression
- Delamination--sealant separating from buoy [14]
The standard for assessing degradation was suitably modified in order to formulate a scale of degradation appropriate for the unique mycelium material. A scale signifying ‘low’, ‘medium’, ‘high’, and ‘extreme’ levels of degradation were decided upon based on the degree of the above terms, and are defined as follows:
| Characteristics | Low (1) | Medium (2) | High (3) | Extreme (4) |
| Discoloration | little to none | mild change in color in a few places | more than half covered in blotches of color | Entire buoy discolored |
| Cracking | 0-1; 1” long and under | 2-3, up to 3” long | 3-4, 5” and under | 4+, severe cracking |
| Crazing | little to none | one crazing branch | up to 4 crazing points | 5+ points of crazing |
| Flaking | little to none | sealant mildly flaking | sealant mostly gone | sealant decimated |
| Holes | Little to none | 1-2, 1" diameter and under | Up to 4, 1"+/- diameter | 4+, 1"+ diameter |
| Delamination | no delamination to 1cm | up to 5" of delamination | 5"-10" total delamination | over 10" delamination |
| Blistering | little to none | 1-2 blisters causing leak | 2-4 blisters + leak/exposure | 4+ blisters or large leak/exposure |
Figure 13. The above chart describes the scale used to measure degradation based on the definitions of erosive characteristics listed in ASTM C488-05. Specimens were rated for each characteristic on levels 1-4 on the 10th and 40th day of water treatment.
Mechanical Testing for Hardness
Measurements of hardness of the material is an important quality to consider for its possible applications, and in characterizing the mycelium in comparison to other materials. Mycelium buoys were only measured before water treatment, meaning at their maximum hardness. Hardness was tested using a durometer type C in accordance with the standard testing methodology ASTM D2240 before water treatment on each type of mycelium buoy. The durometer readings are based on the amount of force it takes to penetrate the material with an indenting tool [11]. Since there is no standard for the mycelium material specifically, the ASTM D2240 Standard Test Method for Rubber Property was followed as it was best fitting for the material’s consistency and cellular composition. The durometer type C is used for medium-hard rubber, thermoplastic elastomers, paper products, and fibrous materials. There are possible inaccuracies in conducting a hardness test on the material. The first has to do with the different consistencies between the outer skin area, which is pure mycelium (mostly chitin [7]), and the inner composite area, which contains both mycelium and undigested substrate. The hardness test was only conducted on the outermost layer of pure mycelium, and did not consider the hardness of the interior. The second possibility for inaccuracy is that the durometer reading varies when placed on different parts of the object. The outermost layer, though made of pure mycelium, is not entirely homogeneous in thickness. This variation in density and thickness of mycelium on the surfaces is partially due to the way in which it was grown. During growth periods, the material was rotated, taken out of molds, and handled in ways that restricted exposure to air on some sides and enabled exposure on other sides. Exposure to air encourages more growth, thus growth and thickness may be manipulated in this manner. The growth method, described above, for the intention of this experiment did not attempt to calculate or note the timing in which one side was exposed vs. another, or the amount of exposure. Another possible reason for varying densities of mycelium skin is the density and quality of the substrate. Quantifying growth parameters such as these is an area of research yet to be seriously undertaken. Average readings of the whole for each subject were taken by testing the hardness on three locations: the side of the cylinder and on both ends.
RESULTS
Comparing Buoyant Force Results Over Time
According to the Archimedes principle, an object will float as long as the buoyant force balances the object's weight, and as long as the force of gravity does not exceed the buoyant force. The longer the buoys were left in the water, the more water they had absorbed; and thus grew heavier over time (which was the expected outcome). A heavier object requires a greater buoyant force in order to float. Figure 14 & 15 show an increase in buoyant force over time. The yellow bars signify the averages of the initial measurements recorded on 2/11/16, and are all relatively the same for each type. The green bars are average buoyant force measurements from the 10th day of water treatment on 2/21/16, and the blue bars are average measurements taken on the 40th day, 3/21/16. The 3/21/16 data shows a significantly greater buoyant force in all buoy types. The controls, however, exhibited the greatest increase in buoyant force for both subsequent testings. The control group average has a 2,657% buoyant force increase after the full 40-day water treatment. The natural latex group sealed water out most effectively and exhibited the slightest increase of buoyant force over time. The latex average has an 896.8% increase; while the shellac buoys have a 1,673% average increase.
Figure 14. The above chart and graph show the relationship between time and buoyant force based on buoy sealant type (displayed on the vertical axis: control=no sealant, latex, and shellac). Buoyant force (on the horizontal axis) is presented in newtons with standard deviations of uncertainty displayed as error bars. The buoyant force figures are the mean of the data samples, and are also displayed in the data table in newtons.
Comparison of Buoyant Force Over Time (Newtons)
| Buoy Type | 2/11/2016 | 2/21/2016 | 3/21/2016 |
| 1c | 6.50 | 17.13 | 167.85 |
| 2c | 6.20 | 18.60 | 182.32 |
| 1l | 6.20 | 7.09 | 69.45 |
| 2l | 7.09 | 6.79 | 66.56 |
| 3l | 7.38 | 7.38 | 72.35 |
| 4l | 7.09 | 7.09 | 69.45 |
| 5l | 6.79 | 6.79 | 66.56 |
| 1s | 6.50 | 7.68 | 75.24 |
| 2s | 5.91 | 12.70 | 124.44 |
| 3s | 6.79 | 8.86 | 86.82 |
| 4s | 7.09 | 15.95 | 156.27 |
| 5s | 6.50 | 14.17 | 138.91 |
Figure 15. The above chart displays the raw data of buoyant force in newtons, before averaging, whereas c=control, l=latex, and s=shellac.
Comparison of Water Absorbency
Buoyant force is equal to the weight of the liquid that the object displaces. Figure 16 & 17 show the water absorbency over time, which directly correlates with the buoyant force. The average weights are shown in Figure 16, and the raw data is displayed in Figure 17. Over the 40-day water treatment, the average water absorbed for the controls, latex, and shellac is 61.53 oz, 25.12 oz, and 44.35 oz respectively. This means the average % increases of weight gain for control is 285.2%, latex is 108.7%, and shellac is 197.7%. Two of the latex-covered buoys, 1l and 4l, were deteriorating quicker than the other latex buoys (Fig.17). This may be because they were not as evenly coated as the other latex-sealed subjects. However, the latex on average showed the least amount of water absorption, while the control group absorbed the most significant amount of water. 
Figure 16. The graph and chart above compares the control, latex, and shellac buoys’ change in weight from water absorbency over time. The differences in weights before water treatment compared to the 40th day of water treatment are significant.
Water Absorbency Comparison by Weight (oz)
| Buoys | 2/11/2016 | 2/21/2016 | 3/21/2016 |
| 1c | 22.4 | 55.7 | 85.0 |
| 2c | 20.8 | 62.2 | 81.2 |
| 1l | 20.7 | 24.1 | 76.0 |
| 2l | 23.4 | 23.6 | 23.4 |
| 3l | 24.7 | 25.0 | 26.2 |
| 4l | 23.5 | 23.8 | 70.4 |
| 5l | 23.3 | 23.8 | 45.1 |
| 1s | 21.9 | 26.3 | 59.0 |
| 2s | 20.8 | 42.2 | 70.7 |
| 3s | 22.9 | 30.9 | 68.0 |
| 4s | 24.5 | 51.6 | 66.5 |
| 5s | 22.1 | 46.6 | 69.7 |
Figure 17. Water absorbency is represented above by the the weights taken of the individual buoys before water treatment, 10 days after, and on the 40th day. The weights above were taken on a scale, and are in ounces. The amount of water absorbed can be calculated by taking the differences of 3/21/16 weights from the 2/11/16 weights.
Optical Assessments Results
The differences in appearances of the individual buoys over time are represented in Figure 18 & 19 in accordance with the scale articulated in Figure 13. The terminology is defined in the ‘Optical Assessment’ portion of the methodology section. The nature of degradation is dependent on the sealant type, or lack of sealant. Since the control group does not have a hydrophobic sealant or adhesive, the assessment characteristics: cracking, crazing, flaking, delamination, and blistering do not apply, and are labeled as ‘N/A’ (not applicable). The control group, however, did express an extreme amount of discoloration just after the tenth day of water and weathering. The discoloration was different from the shellac and latex buoys in that its chalky white color had dissipated and become transparent. After the 40th day, the control group had darkened overall and had become opaque with blotches of white and brown, with many greenish-black portions.The darkening of color occurred most severely near the inner core area, and was more rusty in color. This may be due to the lack of tribological coatings, leading to more friction between the mushroom material and the insert collet. Having no protective sealants, the control group experienced a greater erosion rate and fretting wear, with both the insert collet and water creating fatigue wear and flow cavitation. The controls displayed a high amount of holes after the 40th day. Additionally, they were found to have the most algae and aquatic organisms (such as crabs, silverfish, and eggs) on them. However, the scope of this experiment did not extend to thorough identification of these aquatic organisms and their interactions with the mycelium buoys.
The latex buoys, due to the consistency and elasticity of the sealant, did not exhibit cracking, crazing, or flaking, and are thus labeled as ‘N/A’. Slight discolorations of bluish browns occurred after the tenth day of treatment around small holes where the latex had deteriorated. There were a few air pockets where areas had been delaminated from blistering. Buoys that had shown small holes after the 10th day had deteriorated more extremely and quicker than the others. In these, the discolorations around the holes extended further, and the latex was more noticeably thinning by the 40th day.
The shellac-covered buoys exhibited all of the degradation characteristics. The bright copper color of the shellac faded lighter and much of it flaked off the buoy, causing quicker deterioration and water absorption. On the 40th day, the shellac was entirely lighter in color and almost as spongy to touch as the control group, because of the amount of water absorbance.
There were some white blotches, and some very dark and smokey-gray areas.
Optical Assessment of Degradation: 10th Day of Water and Weathering Treatment
| 2/21/2016 | |||||||||
| Buoy | Discoloration | Cracking | Crazing | Flaking | Holes | Delamination | Blistering | ||
| 1c | 4 | N/A | N/A | N/A | 1 | N/A | N/A | ||
| 2c | 4 | N/A | N/A | N/A | 1 | N/A | N/A | ||
| 1l | 2 | N/A | N/A | N/A | 2 | 2 | 2 | ||
| 2l | 1 | N/A | N/A | N/A | 1 | 1 | 1 | ||
| 3l | 2 | N/A | N/A | N/A | 1 | 1 | 1 | ||
| 4l | 1 | N/A | N/A | N/A | 1 | 2 | 2 | ||
| 5l | 2 | N/A | N/A | N/A | 2 | 1 | 1 | ||
| 1s | 4 | 2 | 1 | 2 | 2 | 1 | 1 | ||
| 2s | 4 | 2 | 2 | 3 | 3 | 2 | 2 | ||
| 3s | 4 | 2 | 1 | 2 | 2 | 1 | 2 | ||
| 4s | 4 | 2 | 1 | 2 | 2 | 2 | 1 | ||
| 5s | 4 | 2 | 1 | 2 | 2 | 1 | 2 |
Figure 18. The above chart rates the buoys individually on a scale of 1 to 4, whereas 1=low, 2=medium, 3=high, and 4=extreme degradation; and c=control, l=latex, and s=shellac.
Optical Assessment of Degradation: 40th Day of Water and Weathering Treatment
| 3/21/2016 | ||||||||||
| Buoy | Discoloration | Cracking | Crazing | Flaking | Holes | Delamination | Blistering | |||
| 1c | 4 | N/A | N/A | N/A | 3 | N/A | N/A | |||
| 2c | 4 | N/A | N/A | N/A | 3 | N/A | N/A | |||
| 1l | 3 | N/A | N/A | N/A | 3 | 3 | 4 | |||
| 2l | 1 | N/A | N/A | N/A | 1 | 1 | 1 | |||
| 3l | 1 | N/A | N/A | N/A | 1 | 1 | 1 | |||
| 4l | 3 | N/A | N/A | N/A | 3 | 2 | 3 | |||
| 5l | 1 | N/A | N/A | N/A | 1 | 2 | 1 | |||
| 1s | 4 | 3 | 2 | 3 | 3 | 3 | 4 | |||
| 2s | 4 | 3 | 3 | 4 | 4 | 3 | 4 | |||
| 3s | 4 | 3 | 2 | 2 | 3 | 3 | 4 | |||
| 4s | 4 | 3 | 2 | 2 | 3 | 3 | 4 | |||
| 5s | 4 | 3 | 2 | 3 | 4 | 3 | 4 |
Figure 19. The above chart rates the buoys individually on a scale of 1 to 4, whereas 1=low, 2=medium, 3=high, and 4=extreme degradation; and c=control, l=latex, and s=shellac.
Hardness Testing Results
Before water treatment, the hardness was measured for each type of buoy in accordance with ASTM D2240 Standard Test Method for Rubber Property. The control and shellac group have similar hardness, showing average values of 40 and 41 at a force of 16.3 and 17.78 N. This hardness rating is comparable to the hardness of a pencil eraser [11]. The latex group exhibited a lower indicated value on the durometer, meaning it takes less force for the indenter to penetrate the material, and is ‘less hard’. The latex buoys, showing an average of 26, meaning an 11.85 N of force to indent, is comparable to the hardness of natural rubber objects. The durometer hardness depends on the viscoelastic behavior and elastic modulus of the material itself [15]. Though there are many direct relationships between physical traits of a material and its hardness, these relationships are material specific; which should be considered in comparing differing material types.Hardness Results Before Water Treatment--Spring Force Calibration (Type C)
| Area Measured: | Control | Shellac | Latex | ||
| Top | 42 | 34 | 23 | ||
| Center | 34 | 46 | 18 | ||
| Bottom | 44 | 42 | 36 | ||
| Indicated Value Ave. | 40 | 41 | 26 | ||
| Force, (N) Ave. | 16.30 | 17.78 | 11.85 |
Figure 20. The chart above features the average indicated values read from the durometer Type C from the top, center, and bottom of each buoy category. The averages are displayed beneath, as well as the averages converted to spring force calibration force in Newtons.
ASTM D2240 Report data:
Date of Test: 3/17/2016
RH: 46%, ambient temp.:72oF
Handheld Durometer Type C, Model 409C, Serial No. 10405
Pacific Transducer Corp. 2301 Federal Ave, Los Angeles, CA 90064
Cert. No. 1896.01
CONCLUSIONS
The use of non-toxic, mycological composite materials for maritime and outdoor objects is an appealing option due to their buoyancy, cost-effectiveness, low-energy requirement for growth, lack of processed or extracted materials, and compostability. All mycelium buoys stayed intact and visibly above the water surface for the duration of this experiment, while experiencing weathering from sun, rain, and tidal shifts.Though the force of gravity eventually exceeded the buoyant force, and weight in all buoy types increased due to water absorbance, the buoys were all able to stay visibly above the water for at least 40 days. The control group experienced the most degradation, having a weight gain of 285.2% increase. However, the control group individuals did stay intact, and though they had immersed lower into the water by the 40th day of water and weathering treatment, they could still be considered functional depending on their purpose. The shellac-covered buoys absorbed less water than the controls, degrading at a slower rate with a 197.7% increase of weight over the 40 day period. The latex-covered buoys proved to hold water out most effectively at the lowest degradation rate, with a 108.7% weight increase in 40 days. Two of the latex buoys had portions on the surface that were not properly and evenly coated, and therefore degraded quicker, as these thinner portions became cavities where water was able to penetrate. The control group of buoys is projected to stay visibly above water for a maximum of about 60 days, 80 days for shellac, and at least 120 days for latex-covered buoys with even sealant coverage.
Finding non-toxic sealants that are both hydrophobic and biodegradable posed a challenge, and is an issue worth further attention and an opportunity for innovation. Furthermore, the water resistance and impermeability of the sealed buoys depends much on the thickness and amount of sealant applied. The exact amount of sealant used for each subject is difficult to quantify, and was described as ‘number of coats’ for the purpose of this experiment. For further experimentation, quantifying sealant thickness and amount per area covered would be advantageous.
The many variables that affect the projection of the material’s growth, structure, and degradation (such as the length of growth, substrate type, additives of growth, species, growing environment, sealant, degradation environment) implies a vast opportunity for future discoveries. Mechanical tests for hardness and compression before and after water and weathering treatment could be beneficial in the pursuit for new applications of this biotechnology. The mechanical properties of foam composites such as the Ganoderma lucidum mycelium buoy depend much on its relative density. There is no current method in specifying the mycelium to substrate ratio, thus it is difficult to precisely capture what the mechanical properties of the composite material are. Additional experiments with a larger sample size and a variety of species, substrate makeup, sealants, and conditions are necessary to understand exactly how this material can be more efficiently grown, withstand weathering, and be sustainably and substantially integrated into the production market.
ACKNOWLEDGEMENTS
I would like to acknowledge the support of my research supervisor Professor Thomas D. Bruns for his insight, expertise, and excitement for all things mushroom. Sincere gratitude is also extended to Sonia Travaglini for her encouragement, guidance, and contributions to my research. Philip Ross and Sophia Wang are genuinely appreciated for their support and innovative ideas, resources, biotechnology and information sharing.
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about Hannah Nguyen
Hannah Nguyen is a psychotherapist and former researcher with a diverse background in sustainable design, mycology, and environmental science. She holds a Master’s in Counseling Psychology from The Wright Institute and a B.S. from UC Berkeley’s College of Natural Resources, where she conducted research for this paper. A passionate mushroom hunter and surfer, Hannah developed a deep respect for nature, making this research a perfect intersection of her academic and personal interests. After a varied career path, Hannah transitioned to psychotherapy in Berkeley, CA, where she works with individuals, couples, and families. She believes that, like plants and mushrooms, humans are resilient, adaptive, and possess innate wisdom and the capacity for growth, especially when nurtured by the right conditions.