Bismuth oxychloride nanosheets for improvement of flexible poly (vinyl chloride) flame retardancy

Bismuth oxychloride nanosheet modified with silane coupling agent (KH570-BiOCl) was prepared by a facile liquid-phase method and used as a green inorganic flame retardant to replace Sb₂O₃, a conventional flame retardant of flexible poly (vinyl chloride), PVC in short. The as-prepared nanosheet was characterized by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectrometry. Its effect on the flame-retardant performance of PVC was investigated by cone calorimetry test (CCT) in association with thermogravimetric analysis (TGA) as well as condensed-phase and gas-phase analyses by Raman spectroscopy and thermogravimetric–infrared spectrometry, respectively. TGA and CCT results indicated that, as a potential flame retardant of PVC, the as-prepared KH570-BiOCl nanosheet with a thickness of about 30–40 nm had good charring ability and could effectively improve the flame retardancy of PVC. Particularly, the PVC-matrix composite with 3% (mass fraction) of KH570-BiOCl nanosheet exhibited 18.65% of char residue as well as significantly reduced the peak heat release rate (45.3%), peak smoke production rate (55.3%) and total smoke production (31.4%). This is because the BiOCl nanosheet could act as a physical barrier to prevent the heat transfer as well as the release and diffusion of the decomposed products of PVC matrix, while it also could catalyze and promote the formation of char layer in the manner similar to that of gaseous phase of Sb₂O₃. Thus, the KH570-BiOCl nanosheet showed great potential to replace Sb₂O₃ and provided the promising manner to develop an environmental friendly PVC composite.