Dual modified layered double hydroxides reinforced flexible polyurethane foam composites with enhanced mechanical, thermal and fire safety properties

Dual-modified layered double hydroxides (MPLDH) were successfully synthesized through sequential phosphate intercalation and urethane-chain grafting, and subsequently incorporated into polyurethane precursor to fabricate flexible polyurethane foam (PUF) composites with improved mechanical, thermal stability, and flame retardancy. FTIR, XRD, TG-DTG, and SEM-EDS analyses confirmed the successful construction of MPLDH, and the grafted urethane chains significantly improved the compatibility and dispersion of LDH within the polyurethane matrix. Owing to the synergistic effects of enhanced interfacial interaction, regulated pore structure, and phosphorus-assisted catalytic carbonization, the MPLDH acted as an efficient reinforcer for PUF. Among the prepared PUF composites, PUF-MPLDH3 with 3 wt% MPLDH filler exhibited the most balanced performances, showing a tensile strength of 0.40 MPa, elongation at break of 409.8%, compressive stress of 0.19 MPa, limiting oxygen index of 24.2%, prolonged time to ignition of 51 s, and delayed time to the maximum peak heat release rate of 95 s. Compared with the neat PUF, the PUF-MPLDH3 exhibited remarkable reductions in peak heat release rate (15.7%), total heat release (14.7%), and total smoke production (28.2%), together with improved thermal stability and a higher graphitization degree of the residual char. This work provides an effective strategy for simultaneously enhancing the mechanical, thermal, and fire safety of flexible polyurethane foams.