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

Abstract

The development of halogen-free and sustainable flame-retardant waterborne polyurethane dispersions (FR_PUDs) is vital for advanced protective textile applications. In this work, a biobased reactive phosphorus flame retardant, Eugenol-DOPO, was synthesised via the grafting of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) onto eugenol and covalently incorporated into the polyurethane backbone to yield an intrinsically flame-retardant PUDs. The integration of eugenol-DOPO increased the aromatic content, crosslink density, and P-C and P-O bonding within the polymer network, resulting in the modified microphase morphology and enhanced thermal stability. Thermogravimetric analysis (TGA/DTG) showed a clear increase in decomposition onset temperature, reduced maximum mass-loss rate, and higher residual char yield in the FR-PUDs compared to the neat formulation. These improvements were attributed to the effective phosphorus-centered radical trapping mechanism of DOPO and the structural rigidity of the eugenol moiety, which jointly promoted condensed-phase char formation. The synergistic interaction between nitrogen and phosphorus further contributed to the generation of a coherent carbonaceous barrier that limited heat flux and volatile emission during combustion. Coated polyester fabrics exhibited enhanced flame retardancy, improved thermal resistance, and retained flexibility and adhesion without compromising coating uniformity. This study demonstrates the potential of Eugenol-DOPO as a renewable reactive phosphorus flame retardant and provides valuable insight into the structure–property relationships governing the performance of environmentally friendly, high-efficiency FR-PUD coatings for textile protection.

Graphical abstract