News Coatings Technologies
Nanohybrid HP@ZIF advances fire-retardant coatings for steel
Researchers have developed an organic-inorganic hybrid nano-flame retardant, HP@ZIF, that significantly improves fire resistance and smoke suppression of intumescent coatings for steel structures. The system also maintains its protective performance after prolonged water immersion.
Intumescent fire-retardant coatings (IFRCs) have become a key element in enhancing fire safety in steel structures. However, conventional IFRCs face challenges in simultaneously meeting requirements for environmental compatibility, high fire resistance and effective smoke suppression in modern construction applications. A recent study addresses these demands by designing an organic-inorganic hybrid nano-flame retardant, HP@ZIF, and combining it synergistically with an ammonium polyphosphate/triazine charring agent (APP/CFA) in an epoxy resin (EP) matrix to produce a high-performance IFRC.
Back-surface temperature testing demonstrated a significant improvement in thermal insulation, supported by a notable increase in char expansion ratio. After 20 minutes of exposure, the backside temperature of the steel plate decreased from 576 °C for the uncoated reference to 187 °C for the S3 coating, corresponding to a heat insulation efficiency of 67.5 %.
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Reduced heat release, smoke and enhanced water resistance
Cone calorimeter testing (CCT) confirmed the enhanced fire safety profile of the coating. Total heat release (THR), total smoke release (TSR) and fire growth rate (FIGRA) were reduced by 70.1 %, 72.0 % and 90.2 %, respectively, compared with the reference. These results indicate a marked improvement in both flame retardancy and smoke suppression, two critical factors for occupant safety and structural integrity during fire events.
Scanning electron microscopy (SEM) and Raman spectroscopy revealed the formation of a dense and continuous char layer after combustion, exhibiting enhanced mechanical integrity and thermal barrier functionality. Notably, the epoxy coating retained its superior fire resistance after 7 days of water immersion, an important requirement for real-world applications where coatings may be exposed to moisture during their service life. According to the authors, the HP@ZIF-based system offers an economical and efficient route to fire protection for modern buildings, combining functional performance with practical durability.
Source: Bao, Q. et al., Hierarchical hybrid nano-structured flame retardant HP@ZIF for improving fire resistance and smoke suppression of intumescent fire-retardant coatings. Journal of Coatings Technology and Research 23, 2775–2789 (2026).
