  A novel method was developed for the sampling of volatiles produces by
polymer decomposition during UL94 standard flammability tests, allowing to
collect, separate and analyze the precise composition of the fuel mixture
feeding the flame in the real flammability tests. The system was validated on
epoxy resin/polyhedral oligomeric silsesquioxanes and found extremely
informative for the understanding of the flame retardancy mechanisms of POSS,
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 to depict a
comprehensive decomposition pathway for the epoxy resin. Lightweight volatiles,
gaseous at room temperature, showed limited differences as a function of
DOPO-POSS, 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
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.
