The new materials belong to a class known as mycelium biocomposites, in which the vegetative root-like networks of fungi are grown through organic substrates such as agricultural residues. The fungal hyphae bind the loose lignocellulosic particles into a solid, relatively lightweight structure that is biodegradable and recyclable. Historically an experimental biomaterial, mycelium composites have attracted growing attention because of their promising combination of low weight, thermal insulation capacity, and reasonable strength and durability. Their production also offers a route to valorizing by-products, storing atmospheric carbon dioxide, and reducing dependence on petrochemicals, all while embodying circular economy principles in which materials can be disassembled, reused, and ultimately returned to natural systems.

Producing these composites is a multi-phase biological process rather than an industrial extrusion. Mycelium is first grown on a substrate over one to two weeks under carefully controlled conditions, typically at temperatures between 24 and 30 degrees Celsius and humidity levels of 60 to 75 percent. The material then develops for two to four weeks as the fungal network colonizes the substrate into a uniformly dense structure. A final drying stage, lasting from a few days to a week, halts fungal growth and provides the strength and dimensional stability that make the material usable in construction. Each of these steps, along with the choice of substrate and fungal strain, shapes the physicochemical characteristics of the finished composite.

In the new study, a research team prepared four experimental series of mycelium biocomposites, each with a different composition, production flow, and specimen geometry. Series I combined wheat straw with Ganoderma lucidum, Series II paired flax straw with Pleurotus ostreatus, Series III used hemp shives with Pleurotus ostreatus, and Series IV tested wheat straw, hemp shives, and flax straw, each inoculated with Ganoderma lucidum. All samples were produced by mixing 7.5 grams of colonized grain spawn into 300 grams of sterilized straw, a spawn-to-substrate ratio of 2.5 percent, with the sterilized substrate held at approximately 60 percent preparative moisture. The mixtures were compressed by hand into cardboard molds shaped as cubes, cylinders, or rectangular prisms, then cultivated and dried under formulation-specific conditions before testing.

The team evaluated four parameters most relevant to insulation performance: thermal conductivity, density, flexural strength, and compressive strength. Density was measured with a precision laboratory balance and manual dimensional measurements, while thermal conductivity was assessed with a portable Isomet 2114 heat transfer analyzer under controlled laboratory conditions of 20 degrees Celsius and 50 percent relative humidity. Each specimen was measured twice on adjacent surfaces, with the median value used for analysis. The researchers also computed a thermal conductivity-to-weight ratio, an inverse indicator that favors formulations combining low heat conduction with low bulk density, to compare the overall thermal-mass balance of the tested materials.

The results revealed striking differences among the formulations. Thermal conductivity ranged from 0.0385 to 0.0719 watts per meter-kelvin depending on substrate and fungal strain, while densities spanned from 80 to 227 kilograms per cubic meter. The standout performer was the hemp shive composite inoculated with Pleurotus ostreatus, which achieved the lowest density range of 80 to 120 kilograms per cubic meter and the most efficient thermal conductivity, from 0.0385 to 0.057 watts per meter-kelvin. This formulation recorded the highest thermal conductivity-to-weight ratio of 0.209, approximately 35.7 percent higher than the next best formulation in the study. By contrast, the multi-material Series IV showed the widest variability in both density and conductivity, reflecting the challenges of consistency in mixed compositions.

Mechanical testing of the optimal hemp shive and Pleurotus ostreatus composite produced equally notable results. Two independently molded prism specimens, each 40 by 40 by 160 millimeters, were subjected to three-point bending on a standardized flexure testing device with a 100-millimeter support span. The composite achieved an average flexural strength of 8.85 megapascals, with individual specimens reaching 8.58 and 9.11 megapascals. Compressive testing on the uncracked halves of the broken prisms yielded an average compressive strength of 4.25 megapascals. Both values exceed or match similar mycelium-based composites described in the literature, where flexural strengths have typically ranged from 0.44 to 4.23 megapascals depending on substrate, and many lignocellulosic formulations have shown compressive strengths below 1 megapascal.

To contextualize these findings, the researchers benchmarked their data against seven published studies of mycelium composites made from comparable plant-derived substrates, plotting thermal conductivity jointly with density because porosity and density strongly influence thermal performance. The literature dataset spans roughly 0.035 to 0.096 watts per meter-kelvin across a wide density range. The hemp shive composite’s minimum conductivity of 0.0385 watts per meter-kelvin compares favorably with values reported for birch sawdust composites and mycelium-bound fibers from invasive plants, and its combination of approximately 100 kilograms per cubic meter density with low conductivity places it firmly in the favorable low-density, low-conductivity region of the performance map. The authors caution, however, that differences in specimen geometry, moisture state, processing conditions, and measurement procedures mean such comparisons serve as performance benchmarking rather than a strictly standardized ranking.

The researchers supplemented their measurements with scanning electron microscopy of the wheat straw and Ganoderma lucidum formulation, which revealed an interconnected filamentous network bridging the lignocellulosic structural elements and numerous micrometer-scale voids. These images provide qualitative evidence of the porous microstructure that underpins the materials’ insulating behavior, although porosity was not quantitatively determined. The team also conducted a rigorous uncertainty analysis, estimating measurement-related uncertainties of roughly 0.6 to 1.3 percent for density, 6.4 to 7.6 percent for thermal conductivity, 3.0 percent for flexural strength, and 2.0 percent for compressive strength, ensuring the reported values rest on a transparent methodological foundation.

The implications extend beyond the laboratory. The hemp shive and Pleurotus ostreatus composite appears suitable for non-load-bearing panels, partition walls, insulation boards, and lightweight structural components, applications where its combination of insulation efficiency, mechanical cohesion, and biodegradability offers genuine advantages over conventional materials. The authors emphasize that their mechanical values rest on limited replication and that future work must address scalability, fire behavior, moisture resistance, biological durability, ageing, dimensional stability, and industrial-scale manufacturability before building-scale deployment. Nevertheless, the study provides practical guidance for future research, industrial pilot projects, and policy-driven adoption of eco-composites. As the construction sector confronts its outsized carbon footprint, materials grown from fungal networks and farm waste are moving from curiosity toward credible contender, proving that the walls of future buildings might one day be cultivated in a matter of weeks.

Subject of Research: Thermal and mechanical performance of mycelium-agricultural waste biocomposites for building insulation

Article Title: Mycelium–Agriwaste Biocomposites for Cleaner Building Insulation: Thermal and Mechanical Performance

Article References: Babenko, M., Kononets, Y., Kunes, R., Makys, P., Spalek, F., Sramhauser, K., Hanzal, P., Majernik, J., Zoubek, T., & Bartos, P. (2026). Mycelium–Agriwaste Biocomposites for Cleaner Building Insulation: Thermal and Mechanical Performance. Cleaner Engineering and Technology, Article 101334. https://doi.org/10.1016/j.clet.2026.101334

Image Credits: AI Generated

DOI: 10.1016/j.clet.2026.101334

Keywords: mycelium biocomposites, building insulation, hemp shives, Pleurotus ostreatus, Ganoderma lucidum, thermal conductivity, agricultural waste, sustainable construction, circular economy, flexural strength, compressive strength, lignocellulosic substrates

The new material, described in the journal Advances in Industrial and Engineering Chemistry, belongs to a family of polymers known as non-isocyanate polyurethanes, or NIPUs. The concept dates back to 1957, when chemists E. Dyer and H. Scott first demonstrated that cyclic carbonates and amines could be reacted to form urethane bonds without any phosgene chemistry. In the decades since, the approach has attracted renewed attention as a safer, more sustainable route to polyurethane-type materials. Instead of combining polyols with isocyanates, NIPU chemistry couples carbonates with amines, sidestepping the most dangerous reagents in the conventional process. But the technology has struggled to catch up in one crucial application: rigid foams for building insulation, where conventional polyurethane foams still dominate the market.

The problem, the researchers explain, is that non-isocyanate rigid polyurethane foams developed so far have suffered from two crippling weaknesses: low mechanical strength and poor flame retardancy. Building insulation must withstand compressive loads behind walls and cladding, and it must resist ignition in an age of increasingly strict fire codes. Earlier attempts to make green foams from glucose or starch produced materials that either crumbled under pressure or burned too readily for commercial use. Glucose-based foams made with maleic acid and glutaraldehyde, for instance, showed low thermal stability, while even tannin-based foams, though somewhat more fire-resistant, still fell short of the flame-retardant performance of commercial foams treated with conventional additives.

The Kyonggi team, led by corresponding author Sang-Bum Kim with first author Sung Yeol Lim, turned to an unlikely hero: tannic acid, the polyphenolic compound familiar to anyone who has tasted an over-steeped cup of tea. Tannic acid brings a rare combination of properties to polymer chemistry. Its multiple aromatic rings lend rigidity and strength to the polymer network, while its abundance of hydroxyl groups makes it highly reactive, readily forming bonds with carbonate reagents and crosslinking agents. Most intriguingly, tannic acid is naturally flame-retardant: it can suppress flames, absorb heat generated during combustion, and promote the formation of a stable char layer that shields the underlying material from heat and oxygen. In other words, the fire protection is built into the molecule itself rather than bolted on with halogenated additives.

The synthesis proceeded in two stages. First, the researchers dissolved tannic acid in water and reacted it with dimethyl carbonate at 65 degrees Celsius to produce carbonated tannin, a carbonate-bearing intermediate. Spectroscopic analysis confirmed the transformation: the infrared spectrum showed the disappearance of the carbonyl peak characteristic of dimethyl carbonate at 1740 wavenumbers and the emergence of a new carbonyl peak at 1711 wavenumbers, while proton nuclear magnetic resonance revealed a methoxy signal at 3.46 parts per million absent from the starting material. The carbonated tannin was then reacted with hexamethylenediamine at 90 degrees Celsius for two hours, yielding a tannic acid-based non-isocyanate polyurethane resin whose urethane bonds were confirmed by characteristic infrared peaks for the carbonyl, nitrogen-hydrogen, and carbon-oxygen groups.

The critical innovation lay in the formulation of the foam itself. The team blended the resin with three crosslinking agents, each playing a distinct role: hexamethylenetetramine and glutaraldehyde extend the polymer chains and build crosslink density, while citric acid reacts with the amine groups in the resin and acts as a foaming inducer, generating the gas bubbles that turn a liquid resin into a lightweight foam. By systematically varying the amounts of these three agents across six formulations, the researchers could dissect exactly how each one shaped the final material. The differences were dramatic. In the formulation lacking glutaraldehyde, the foam expanded rapidly and then collapsed entirely, demonstrating that sufficient crosslinking is essential to stabilize the expanding bubble structure. All formulations containing adequate crosslinker produced stable foams of similar density.

Compressive testing revealed a clear winner: the formulation with the highest crosslinking agent content, designated F-1, exhibited the highest compressive strength of all. Scanning electron microscopy explained why. The F-1 foam displayed the smallest and most uniform cells, a microstructure that distributes mechanical stress evenly across the material and prevents cracks from propagating. The microscopy also illuminated the role of each additive. Without hexamethylenetetramine, the crosslinking reaction slowed, reducing reaction heat and delaying curing so that growing cells merged into larger, weaker pores. Without citric acid, no cells formed at all, confirming its role as the foaming trigger. And with less glutaraldehyde, cell sizes grew larger for the same kinetic reasons. The message was consistent: faster, denser crosslinking yields finer, stronger foam.

The fire performance was where the material truly distinguished itself. In thermogravimetric analysis, the tannic acid foam left behind roughly 25 percent char residue after heating to 550 degrees Celsius in nitrogen, compared with only about 15 percent for a conventional polyurethane foam of similar density, reflecting the char-forming tendency of tannic acid’s aromatic structure. Adding citric acid shifted the maximum decomposition rate of the urethane bonds to higher temperatures, from around 285 to 303 degrees Celsius, confirming that the crosslinked network improved thermal stability. In limited oxygen index testing, the new foam required a higher oxygen concentration to sustain burning than the conventional foam, and derivative analysis attributed the protection to tannic acid’s aromatic rings, which promote a stable char barrier, and to phenoxy radicals that quench the oxygen free radicals released during polymer decomposition.

The ignition test provided the most vivid demonstration. When a butane torch flame was applied directly to the specimens for twenty seconds, the conventional polyurethane foam burned rapidly, retaining only 23.3 percent of its original mass. The tannic acid-based foam resisted ignition, and any flames that did appear extinguished themselves within roughly two seconds, leaving about 90 percent of the mass intact. Photographs taken after the test show the conventional foam reduced to charred wreckage while the tannic acid foam retained its shape, a striking visual testament to the power of molecularly embedded fire protection. Notably, flame retardancy varied little across the different crosslinking formulations, suggesting that the fire resistance stems primarily from the tannic acid backbone itself.

The study’s conclusions point toward a future where building insulation no longer requires either phosgene-derived isocyanates or halogenated flame retardants. By tuning the balance of hexamethylenetetramine, citric acid, and glutaraldehyde, the researchers showed that crosslinking agents can simultaneously enhance mechanical strength, thermal stability, and structural integrity, addressing the two key limitations that have kept non-isocyanate foams out of commercial buildings. Challenges remain before tannic acid foams line the walls of skyscrapers, including scaling the synthesis and meeting the full battery of building-code certifications. But the demonstration that a plant-derived polyphenol can deliver both strength and self-extinguishing fire behavior in an isocyanate-free foam marks a significant advance for sustainable materials chemistry, and a compelling argument that the safest flame retardant may be the one grown in a tree.

Subject of Research: Tannic acid-based non-isocyanate rigid polyurethane foam with tunable crosslinking for improved mechanical strength and flame retardancy

Article Title: Study on the mechanical properties and flame retardancy of tannic acid-based non-isocyanate rigid polyurethane foam according to the content of crosslinking agents

Article References: Lim, S. Y., Park, S. B., Kim, M. S., & Kim, S.-B. (2025). Study on the mechanical properties and flame retardancy of tannic acid-based non-isocyanate rigid polyurethane foam according to the content of crosslinking agents. Advances in Industrial and Engineering Chemistry, 1(1), Article 15. https://doi.org/10.1007/s44405-025-00015-y

Image Credits: AI Generated

DOI: 10.1007/s44405-025-00015-y

Keywords: non-isocyanate polyurethane, tannic acid, rigid foam, crosslinking agents, flame retardancy, mechanical properties, building insulation, sustainable polymers, thermal stability, char formation, green chemistry, phosgene-free synthesis