POLYAROMATIZATION IN COMMON SYNTHETIC-POLYMERS AT ELEVATED-TEMPERATURES

Thermal decomposition reactions of polyethylene and phenolformaldehyde novolac were studied at 800-1000-degrees-C by pyrolysis-gas chromatography/mass spectrometry. The main high temperature products of both polymers are benzene, naphthalene, acenaphthene and phenanthrene; moreover, dibenzofuran and xanthene are also formed from phenolformaldehyde novolac. A high temperature decomposition mechanism is proposed for polyethylene through conjugated polyene formation, aromatic ring closure and fusion. For phenolic novolac several other reactions are considered such as condensation or reduction of phenolic hydroxyl groups, decomposition of phenol rings into carbon monoxide and pentadienylene biradical, and attachment of the biradical to an aromatic ring resulting in bi- and tricyclic aromatic volatiles. High temperature pyrolysis experiments have also been carried out in the presence of some inorganic materials. The effect of additives has been interpreted in terms of promoting or hindering the reactions yielding polyaromatic volatiles. Polyaromatization and condensation are advanced by additives of high surface area (gamma-alumina and activated charcoal) and retarded by potassium carbonate, iron, ferric oxide, copper and cupric oxide.