Highly Efficient and Green Multi-layer Coatings toward Enhancing Impact Resistance, Flame Retardancy and Thermal Insulation of Flexible Polyurethane Foam

In extreme environments, the simultaneous presence of mechanical impact and fire hazards poses significant challenges for single flexible polyurethane foam (FPUF) protective materials. To address these limitations, we developed an innovative multilayer coating structure for FPUF using a simple dip-drying method. This structure comprises a polydopamine (PDA) base layer, an intermediate layer containing ammonium polyphosphate (APP), carboxymethyl chitosan (CMC), and halloysite nanotubes (HNT), and a top layer of polydimethylsiloxane (PDMS). The multilayer coating significantly enhanced the cushioning and flame-retardant properties of FPUF. At a coating loading of 35 wt.%, the FPUF@PDA/A-C-H/PDMS exhibited a compressive strength 3.52 times higher than pure FPUF, with only a 10.2% decrease after 100 compression cycles. The composite effectively dissipated 95.7% of an impact energy of 1.22 J, achieving a 97.1% impact force dissipation rate and significantly extending cushioning duration. The FPUF@PDA/A-C-H/PDMS demonstrated self-extinguishing properties after 10 s of exposure to a butane flame, maintaining structural integrity. Moreover, its peak heat release rate was reduced by 68.8%. The multilayer coating also improved hydrophobicity and thermal insulation. This multifunctional foam composite shows great potential for enhancing the performances of FPUF in hazardous environments, offering robust protection in extreme conditions.