Synergistic effect of cocondensed nanosilica in intumescent flame‐retardant polypropylene

Amino‐functionalized nanosilica (SiO 2 ‐NH 2 ) was prepared through cocondensation method using aminopropyltriethoxysilane as comonomer to hydrolyze and cocondense with tetraethylorthosilicate. The synergistic effect of combination of ammonium polyphosphate and pentaerythritol with SiO 2 ‐NH 2 on the thermal and flame‐retardant properties of intumescent flame‐retardant (IFR) polypropylene (PP) has been investigated by thermogravimetric analysis (TGA), scanning electron microscopy, Raman spectra, X‐ray diffraction (XRD), limiting oxygen index (LOI), and UL 94 tests. When 1.0 wt.% SiO 2 ‐NH 2 was added, the LOI value of the PP/IFR composite with 25 wt.% of IFR increased from 26.6% to 31.7%, while the UL 94 rating raised from not classified to V‐0. The TGA data demonstrated that the SiO 2 ‐NH 2 nanoparticles increased the charred residue of the PP/IFR composites. The morphological structures and the orderliness of the charred residue proved that SiO 2 ‐NH 2 promoted the formation of compact intumescent charred layer, which effectively protected the underlying polymer from burning. The XRD patterns of the charred residue indicated that nanosilica reacted with APP to form SiP 2 O 7 crystal structure during combustion, which was beneficial to the formation of compact charred layers. In comparison with the inorganic SiO 2 ‐cal nanoparticles, the amino‐functionalized nanosilica revealed much more efficient synergistic flame‐retardant effect due to the difference of surface properties.