Dual-functional composite coating with flame-retardant and antibacterial properties for flexible polyurethane foams†

Abstract

Dual functionalization of polyurethane (PU) foam to achieve both flame-retardant and antibacterial properties is crucial for meeting stringent fire safety and hygiene standards. Herein, an efficient dual-functional coating, PDA@CS-POM, is developed by combining a transition metal-substituted polyoxometalate (POM), [Co₄(H₂O)₂(PW₉O₃₄)₂]¹⁰⁻, with a catecholamine-tethered polycation (PDA@CS(+)) prepared with polydopamine (PDA) and chitosan (CS), through a straightforward layer-by-layer (LbL) assembly method. The catecholamine groups in PDA@CS enable effective LbL assembly on hydrophobic silicon wafers and flexible PU foams without substrate pre-treatment. In particular, the PDA@CS-POM coating achieves a growth rate of 11.3 nm per BL, more than twice that of the reference CS-POM coating without PDA. Compression-recovery cycles demonstrate that the PDA@CS-POM coating increased the toughness of the PU foam while maintaining its inherent resilience. Assessments including limiting oxygen index (LOI), cone colorimetry, zone of inhibition, and colony culture tests confirm the efficient flame-retardant and antibacterial properties of the PDA@CS-POM coated PU foams. These dual-functional properties of the PDA@CS-POM coating positively correlate with the effects of the POM in inhibiting foam degradation, improving graphitization/aromatization of char barrier, and disrupting bacteria redox processes or cytoskeleton dynamics.