Blowing-out effect and temperature profile in condensed phase in flame retarding epoxy resins by phosphorus-containing oligomeric silsesquioxane

A series of flame retardant epoxy resins (EPs) containing phosphorus-containing oligomeric silsesquioxane are prepared, and an interesting blowing-out effect is detected in flame retardant EPs. The temperature profiles show that blowing-out effect slows the heat transfer from the fire to the unburned matrix; furthermore, this blowing-out effect can even take away some heat from the surface zone by the spurting gases. The thermo gravimetric analyzer and Fourier transform infrared spectrometer result shows that the spurting gases during the blowing-out effect have a high content of CO₂, which could reduce the combustion capability of the jetting gases. The flame retardancy of these EPs is tested by limit oxygen index and UL-94. The incorporation of 2.5wt% phosphorus-containing oligomeric silsesquioxane into EP gives a remarkable blowing-out effect, which results in a significant enhancement of limit oxygen index value and UL-94 rating. The flame retardancy mechanism of blowing-out effect is quite different from the traditional mechanisms. The char strength and morphology of EP composites are also investigated to explain the mechanism of the blowing-out effect.