Synergistic effect of piperazine pyrophosphate and epoxy-octavinyl silsesquioxane on flame retardancy and mechanical properties of epoxy resin

In order to solve the contradiction between the flame retardancy and mechanical properties of epoxy resin, piperazine pyrophosphate (PAPP) and epoxy-octavinyl silsesquioxane (EOVS) are applied as flame retardants for epoxy resin (EP). With the introduction of PAPP and EOVS, the properties of the EP composites about flame retardancy, mechanical properties and smoke suppression are significantly improved. EP/9 wt% PAPP/1 wt% EOVS (EP3) passes a vertical burning (UL-94) test V-0 rating and acquires the limiting oxygen index (LOI) test value of 32.4%. The results of cone calorimeter (CC) tests confirm that the incorporation of PAPP and EOVS significantly reduces the total heat release (THR), peak heat release (PHRR), total smoke production (TSP) and peak smoke produce rate (PSPR) values, which are respectively decreased by 25%, 81%, 57% and 63% compared with those of pure EP. Scanning electron microscope (SEM), energy dispersive spectrometry (EDS), Laser Raman spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS) and Thermogravimetry-Fourier transform infrared (TG-FTIR) spectroscopy are adopted to analyze the flame-retardant mechanism of PAPP/EOVS flame retardants. These results reveal that the flame retardancy of EP3 is attributed to the excellent charring ability, the dilution effect of non-combustible gases and the flame inhibition of gaseous phosphorous compounds. Besides, the tensile and impact strength of EP3 increase benefitting from the presence of epoxy groups and Si-O bonds in EOVS. This work proposes a new method to prepare the mechanically reinforced and flame-retardant epoxy resin.