FTIR and GCMS analysis of epoxy resin decomposition products feeding the flame during UL 94 standard flammability test. Application to the understanding of the blowing-out effect in epoxy/polyhedral silsesquioxane formulations

A novel method was developed for the sampling of volatiles produced by polymer decomposition during UL-94 standard flammability tests, allowing collecting, separating and analyzing the precise composition of the fuel mixture feeding the flame in the real flaming conditions. The system was validated on epoxy resin/Polyhedral Oligomeric SilSesquioxanes (POSS) and found extremely informative for the understanding of the flame retardancy mechanisms previously referred to as the “blowing-out effect”. Collected products were analyzed by infrared spectroscopy and gas chromatography/mass spectroscopy, to identify the gaseous and liquid decomposition products, allowing depicting a comprehensive decomposition pathway for the epoxy resin. Lightweight volatiles, gaseous at room temperature, showed limited differences as a function of DOPO-POSS (polyhedral oligomeric silsesquioxane functionalized with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide), whereas mixtures of liquid products evidenced for dramatic changes in the relative concentration as a function of DOPO-POSS. In pristine epoxy resin, the most abundant products were recognized as benzene, phenol, naphthalene and toluene, along with several tens of other aromatic products observed in lower amounts. The presence of DOPO-POSS at low concentration (2.5%) radically changes the composition of the aromatic volatiles mixture, as no significant amount of benzene is produced, while phenol becomes the main product, accounting for about half of the total, isopropyl phenol and bisphenol A, along with several tens of other products in lower concentrations. Such modification of the fuel mixture feeding the flame provided an explanation for the lower flammability of this formulation, as well as for the phenomenology of the blowing out effect.