Stabilizing effect of sepiolite in the preparation of flame-resistant expanded perlite/semi-rigid polyurethane foam composites

While additive-type flame retardants (FRs) offer ease of application, they may exhibit incompatibility with polyurethane (PU) foams at elevated concentrations, potentially compromising mechanical and morphological properties. This study examines the stabilizing influence of sepiolite (S) on expanded perlite (EP)-doped semi-rigid PU foams (SrPUFs). The thermal stability, morphological structure and flame resistance of S_SrPUF, S_EP_SrPUF and EP_SrPUF samples were evaluated using TGA, SEM and the UL 94 vertical combustion test, respectively. The TGA results indicated a 3.27-fold increase in char residue in the S_EP_SrPUF sample containing sepiolite compared to SrPUF. Additionally, this sample demonstrated a uniform structure akin to pure foam and halted tar flow, extending the combustion time from 50 to 96 s. The S_EP_SrPUF sample, incorporating 2% sepiolite and 8% EP additives, exhibited enhanced strength and flexibility, with mechanical performance improving by 38.4%. The findings suggest that the incorporation of sepiolite with additive-type FRs enhances FR efficacy by establishing a structural equilibrium between the foam matrix and the additive. This study provides significant contributions to both academic and industrial domains. © 2025 Society of Chemical Industry.