Preparation of a flame retardant phosphorus-containing polyacrylate/α-zirconium phosphate nanocomposite through in situ emulsion polymerization

Abstract

An acrylamide modified α-zirconium phosphate (AM-ZrP) was prepared by intercalating acrylamide into the α-zirconium phosphate (α-ZrP), and was utilized to synthesize a flame retardant phosphorus-containing polyacrylate/α-zirconium phosphate (PPA/AM-ZrP) nanocomposite via in situ emulsion polymerization. The AM-ZrP was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The layered structure and morphology of AM-ZrP in the PPA matrix were studied by XRD and transmission electron microscopy (TEM). Effects of AM-ZrP content on the monomer conversion, polymerization stability, thermal properties and flame retardancy of the PPA/AM-ZrP nanocomposite were studied. The flame retardant mechanism of AM-ZrP was also discussed. Results showed that the acrylamide was successfully intercalated into the α-zirconium phosphate. The incorporation of AM-ZrP would increase the T_g of the composite. When 0.5 wt% of AM-ZrP was added, the exfoliated AM-ZrP nanoplatelets were covered by a layer of PPA polymer, and well dispersed in the PPA matrix. Meanwhile, the PPA/AM-ZrP composite had a lower peak heat release rate (pHRR) and higher limiting oxygen index (LOI) than the PPA, indicating that the PPA/AM-ZrP composite possessed better flame retardancy. With the further increase of the AM-ZrP content to 3.0 wt%, the AM-ZrP nanoplatelets came together, forming big aggregates and showed poor dispersion in the composite, which had adverse effects on the flame retardancy of PPA/AM-ZrP. SEM and energy dispersive X-ray spectroscopy (EDS) analysis suggested that the existence of AM-ZrP in the PPA/AM-ZrP composite could catalyze the carbonization process and promoted the formation of a compact char layer, which was favorable for the improvement of flame retardancy of the composite.