POSS A SYNERGIST FOR FIRE RETARDANT EPOXY RESIN /APP SYSTEM: MECANISM OF ACTION

摘要

This study deals with the fire retardancy of epoxy resins. Ammonium PolyPhosphate (APP), a traditional fire retardant (FR) and Octamethylpolyhedral oligomeric silsesquioxane (OMPOSS) were used. First, the FR were studied alone then in combination. After characterization by Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM), reaction to fire was evaluated by mass loss calorimetry. It is noteworthy that with only 5 wt.-% loading of fillers, a significant decrease of the peak of heat of release rate (pHRR) via an intumescence phenomenon is observed, i.e -50%, -48%, -68% for Epoxy/APP, Epoxy/OMPOSS and Epoxy/APP/OMPOSS respectively, compare to pure epoxy. The study of the char structures, its inside temperatures and its swelling permit to elucidate the mode of action of these intumescent systems. It was determined that the viscosity of the system is the key of fire retardancy mechanism. Indeed in the case of Epoxy/APP, the char formed during swelling is not strong enough to trap evolving gases leading to higher flammability than Epoxy/APP/OMPOSS. This latter system releases less gas because of better viscosity trapping those gases and permitting a bigger swelling concomitantly to the formation of 'foamy' char (small bubbles (voids) evenly distributed in the char structure).