Flammability and thermal behavior of polypropylene composites containing dihydrogen phosphate anion‐intercalated layered double hydroxides

Dihydrogen phosphate anion‐intercalated layered double hydroxides (M‐LDHs) was prepared by modification of Mg‐Al‐CO₃²⁻ layered double hydroxides (LDHs) with anion exchange procedure. The structure of the M‐LDHs was characterized by X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscope (TEM). Polypropylene (PP)/LDHs and PP/M‐LDHs composites were prepared by melt compounding. The morphology of PP composites was investigated by TEM and XRD, which demonstrated that M‐LDHs could be well dispersed in PP matrix to form a nano‐scale exfoliated structure. Thermogravimetric analysis showed that thermal stability of PP composites was improved by the presence of LDHs and M‐LDHs. The flammability of PP composites was characterized by limited oxygen index, vertical burning test (UL‐94), FTIR, and cone calorimeter test, and the result showed the fire performance were significantly improved after the addition of LDHs and/or M‐LDHs which can remarkably decrease the heat release rate, total heat release, and the fire performance index. It was proposed that the lamellar structure of LDHs can block the heat, dilute the flammable gases and decrease the temperature, while the replaced H₂PO₄⁻ into LDHs molecules can enhance the charred layer formation during burning procedure. Inductively coupled plasma mass spectrometer analysis showed that most phosphorus remained in the char layer, suggesting the replaced H₂PO₄⁻ in LDHs molecules mainly function in the condensed phase. POLYM. COMPOS., 36:2230–2237, 2015. © 2014 Society of Plastics Engineers