Organic–inorganic hybrid flame retardant: preparation, characterization and application in EVA

A novel organic–inorganic hybrid flame retardant (DOPA–ATH), which was prepared via reacting dibenzo[c,e][1,2]oxaphosphinic acid (DOPA) with aluminum trihydroxide (ATH), was incorporated in ethylene-vinyl acetate copolymer (EVA) to improve its flame retardance. The structure, morphology and thermal stability of the hybrid flame retardant were characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The results suggested that DOPA was grafted onto ATH successfully, therefore resulting in higher thermostability than ATH. The flame retardance and burning behaviour of EVA with DOPA–ATH were also studied using limiting oxygen index (LOI), Underwriter laboratory 94 vertical burning test (UL-94 V) and cone calorimeter test (CCT). Results of UL-94 tests and LOI tests showed that the flame retardance of EVA/DOPA–ATH was better than EVA/ATH binary and EVA/DOPA/ATH ternary flame-retardant composites. The data obtained from the CCT showed that the peak heat release rate (PHRR) of EVA with the addition of 50 wt% DOPA–ATH was reduced by about 25% comparing with EVA with equivalent ATH. Total heat release (THR) and total smoke production (TSP) were reduced remarkably as well. The thermogravimetric analysis (TGA) data showed that the thermal stability of EVA/DOPA–ATH was improved with increased initial decomposition temperature and char residue. SEM observations of cryogenically fractured and tension fractured surfaces showed that EVA/DOPA–ATH had better interfacial interaction comparing with those of EVA/ATH and EVA/DOPA/ATH, which resulted in better elongation at break and tensile strength.