News Coatings Technologies
Copper nanoclusters boost flame and microbial resistance of WPU
Researchers have engineered a water-borne polyurethane composite by incorporating casein-templated copper nanoclusters as a green multifunctional nanofiller. The system integrates enhanced flame retardancy, strong antimicrobial activity, improved mechanical performance and hydrophobicity, offering a promising approach for multifunctional coating applications.
Water-borne polyurethane (WPU) is an eco-friendly polymer system that is widely used in coatings, adhesives and elastomers. However, its inherent flammability and susceptibility to microbial degradation significantly compromise its long-term durability and operational safety. To address these limitations, Jin and colleagues developed a synergistic engineering strategy based on casein-templated copper nanoclusters (CuNCs@Casein), which serve as a multifunctional nanofiller for WPU composites.
At the optimal loading of CuNCs@Casein, the WPU composites demonstrated significantly improved fire safety. The limiting oxygen index (LOI) increased from 19.14 % to 22.30 %, and the material achieved a UL-94 V-2 rating. In addition, the peak heat release rate (PHRR) and total heat release (THR) were reduced by 25.00 % and 26.10 %, respectively, while smoke production was suppressed by up to 70.00 %, which is particularly relevant for applications where smoke toxicity is a key safety concern.
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Antimicrobial performance and mechanical properties
The incorporation of CuNCs@Casein also imparted strong antimicrobial activity to the WPU composites. Inhibition rates of 98.61 % against Escherichia coli and 98.17 % against Staphylococcus aureus were achieved, together with notable mould resistance. This combination of flame retardancy and antimicrobial performance is particularly interesting for coatings used in hygiene-sensitive or safety-critical environments.
Beyond these functional properties, the composites also showed improved mechanical performance, with simultaneous increases in tensile strength and elongation at break. The composite films underwent a marked transition from hydrophilic to hydrophobic behaviour, as reflected by an increase in the water contact angle from 31.7° to 113.3°. Overall, the work demonstrates a synergistic strategy that integrates flame retardancy, antimicrobial activity, mechanical enhancement and hydrophobicity into a single WPU-based system, providing a promising route for the development of multifunctional water-borne coating solutions.
Source: Jin, C. et al., Synergistic engineering of waterborne polyurethane via casein-templated copper nanoclusters to achieve integrated flame retardancy and antimicrobial activity. Progress in Organic Coatings, 110252 (2026).
