Clove-Derived Flame Retardant Gives Polyester Fabrics a Fire-Resistant, Eco-Friendly Coat

Every year, fires involving textiles claim thousands of lives worldwide, and synthetic fabrics such as polyester are among the most common fuels involved. Polyester is prized for its durability, low cost, and resistance to wrinkling, but it melts and drips when exposed to flame, spreading fire rapidly and causing severe burns. Traditional flame retardants have relied heavily on halogenated compounds, which work well chemically but have come under intense scrutiny because they persist in the environment, accumulate in house dust, and are linked to health concerns. Now, a team of researchers at the Institute of Chemical Technology in Mumbai, India, has developed a flame-retardant coating built from an unexpected source: clove oil. Their work, published in Polymer Bulletin, describes a waterborne polyurethane coating modified with a molecule derived from eugenol, the aromatic compound that gives cloves their distinctive scent, chemically bonded to a phosphorus-containing fire suppressant known as DOPO.

The research, led by Akash R. Parvate with contributions from Suyog Patil under the supervision of Aarti P. More, addresses a long-standing tension in materials science. Flame retardants need to be effective, durable, and safe, but additives that achieve one goal often compromise another. Halogenated retardants are effective but environmentally problematic. Phosphorus-based alternatives are generally considered greener, but many are simply blended into polymers rather than chemically incorporated, meaning they can leach out over time, reducing both performance and safety. The Mumbai team took a different approach: they designed a reactive flame retardant that becomes part of the polyurethane backbone itself, so the fire protection cannot migrate, evaporate, or wash away.

The key innovation lies in the synthesis of a compound the researchers call Eugenol-DOPO. Eugenol, extracted from clove oil, is a naturally abundant phenolic molecule with a rigid aromatic ring structure and a reactive allyl side chain. DOPO, short for 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, is a well-studied organophosphorus compound prized in flame-retardant chemistry for its ability to interfere with the radical reactions that sustain combustion. By grafting DOPO onto eugenol, the chemists created a hybrid molecule that combines the structural rigidity of a plant-derived aromatic with the fire-suppressing power of phosphorus. This modified molecule was then incorporated as a polyol component during the synthesis of a waterborne polyurethane dispersion, meaning the flame retardant is covalently locked into the polymer network rather than merely mixed in.

Waterborne polyurethane dispersions, often abbreviated as PUDs, are an increasingly popular class of coatings because they use water as the carrier medium instead of volatile organic solvents. This makes them attractive from both an environmental and an industrial hygiene standpoint. However, standard polyurethane coatings offer little fire protection on their own. The challenge for the researchers was to build flame retardancy into the dispersion without sacrificing the properties that make polyurethane coatings useful in the first place: flexibility, adhesion, and the ability to form a uniform film on fabric. Their solution was to tune the chemistry so that the Eugenol-DOPO unit participates directly in the polymerization, becoming an intrinsic part of the material rather than an external additive.

The molecular logic behind the design is elegant. When Eugenol-DOPO is incorporated into the polyurethane backbone, it raises the aromatic content of the polymer and increases crosslink density, the degree to which polymer chains are interconnected. Both factors make the material harder to decompose. The phosphorus atoms introduce P-C and P-O bonds into the network, which play a critical role during heating. Thermogravimetric analysis, a technique that measures how a material loses mass as temperature rises, showed that the modified coatings began decomposing at higher temperatures, lost mass more slowly at the point of maximum degradation, and left behind significantly more residual char than the unmodified formulation. In fire science, char is gold: a dense carbonaceous layer acts as a physical barrier that insulates the underlying material, blocks heat transfer, and prevents flammable volatile gases from escaping to feed the flame.

The mechanism responsible for this behavior involves two complementary actions. First, DOPO is known for its phosphorus-centered radical trapping ability. Combustion proceeds through a chain of highly reactive radical species in the gas phase; when DOPO-derived fragments are released, they capture these radicals and break the chain reaction, effectively starving the flame. Second, the rigid eugenol moiety promotes condensed-phase char formation, building the protective carbonaceous barrier directly on the fabric surface. The researchers also point to a synergistic interaction between phosphorus and nitrogen, both present in the polyurethane system. Phosphorus-nitrogen combinations are a classic pairing in intumescent flame-retardant chemistry, where the two elements work together to produce a swollen, coherent char layer that expands to limit heat flux and volatile emission during burning.

When the team applied these modified dispersions as coatings on polyester fabrics, the results confirmed the promise of the approach. Coated textiles exhibited enhanced flame retardancy and improved thermal resistance compared with untreated fabric. Energy-dispersive X-ray analysis detected nitrogen on the textile surface, confirming that the polyurethane coating had deposited uniformly. Crucially, the coatings retained the qualities that matter in real-world textile applications: the fabrics remained flexible, the coating adhered well, and the uniformity of the film was not compromised by the added flame retardant. This balance is often the sticking point in flame-retardant research, where heavily loaded additives can make fabrics stiff, brittle, or prone to delamination.

The broader context makes this work particularly timely. Brominated flame retardants such as polybrominated diphenyl ethers and hexabromocyclododecane have been detected in household dust and are subject to increasing regulatory restrictions across the globe. At the same time, demand for fire-safe textiles continues to grow in sectors ranging from home furnishings and apparel to transportation and public buildings. Waterborne, halogen-free coatings based on renewable feedstocks offer a route to fire safety that aligns with tightening environmental standards and consumer expectations. Eugenol is an especially appealing building block because it is already produced at industrial scale from clove oil, is relatively inexpensive, and has a chemical structure, aromatic ring plus reactive side chain, that polymer chemists can exploit in multiple ways.

The Mumbai study also contributes to a deeper scientific goal: understanding the structure-property relationships that govern how molecular design translates into fire performance. By showing that a single bio-based molecule can simultaneously raise thermal stability, increase char yield, reduce the maximum rate of degradation, and preserve coating quality, the researchers demonstrate that sustainability and performance need not be opposing forces. The finding that covalent incorporation of the retardant modifies the microphase morphology of the polyurethane, the nanoscale arrangement of hard and soft segments, suggests that molecular architecture matters as much as elemental composition. This insight could guide future designs of reactive flame retardants for other polymer systems, including epoxy resins and foams, where DOPO chemistry has already shown promise.

There remains work to be done before such coatings reach commercial production. The study, published in Polymer Bulletin as volume 83, article 666, focused on synthesis, thermal characterization, and coating performance, and large-scale durability testing, wash resistance, and full combustion performance metrics would be natural next steps. Nevertheless, the demonstration that a clove-oil derivative can be transformed into an intrinsically flame-retardant, waterborne polyurethane coating for polyester marks a meaningful advance. It points toward a future where the fabrics that surround us, from sofas to seat covers, can be made significantly safer using chemistry rooted in plants rather than in persistent synthetic halogens, and where fire protection is built into the material itself rather than sprinkled on as an afterthought.

Subject of Research: Bio-based phosphorus flame-retardant polyurethane coatings for polyester textiles

Article Title: Synergistic flame-retardant coating based on eugenol–DOPO modified polyols for enhanced thermal stability of polyester fabrics

Article References: Parvate, A. R., Patil, S., & More, A. P. (2026). Synergistic flame-retardant coating based on eugenol–DOPO modified polyols for enhanced thermal stability of polyester fabrics. Polymer Bulletin, 83(12), Article 666. https://doi.org/10.1007/s00289-026-06723-9

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06723-9

Keywords: flame retardant, eugenol, DOPO, waterborne polyurethane, polyester fabric, thermal stability, char formation, phosphorus-nitrogen synergy, sustainable coatings, halogen-free, textile protection, biobased polymers