Expanded charring flame retardant effect of caged polysilsesquioxane containing Schiff base structure on poly(ethylene terephthalate) combustion

Via a hydrolytic condensation reaction, we successfully synthesized polyhedral oligomeric silsesquioxane containing Schiff base structures (NSPOSS). These were then incorporated into the PET matrix through melt blending, aiming to bolster the flame retardancy of poly(ethylene terephthalate) (PET). The interaction force between NSPOSS and PET was analyzed by simulation of NSPOSS pulling out in PET via MS8.0. Additionally, NSPOSS exhibits excellent flame retardancy and smoke suppression. For PET-10wt%NSPOSS, the peak heat release rate (pk-HRR), the total heat release (THR), the total smoke release (TSR), peak smoke release rate (pk-RSR), and the highest smoke density peak (Ds max) decreased by 60%, 14%, 57%, 42% and 59%, respectively, compared to neat PET. Moreover, PET-NSPOSS composites exhibit char expansion during combustion, for which we propose a charring mechanism. The newly prepared NSPOSS can be applied in various resin matrices, offering promising prospects for practical applications.