Antimony oxide–PVC synergism: Laser pyrolysis studies of the interaction mechanism

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Abstract
Laser‐probe pyrolysis is used to investigate the synergistic flame‐retardancy effect observed for antimony oxide (Sb2O3)–PVC combinations. Molecular beam‐mass analysis detection techniques permit direct sampling of the laser‐vaporized species without the need for intermediate product collection stages. Laser pyrolysis of a PVC formulation containing 3 phr Sb2O3 provides the first direct evidence for the production of volatile SbCl3 during thermal decomposition. Selective laser irradiation of PVC in the presence of unheated Sb2O3 in the sample cell reveals that HCl evolved from the polymer substrate rapidly reacts with Sb2O3(s) to form the volatile flame‐retardant species SbCl3. Similar results are observed for SbOCl(s). These reactions are distinct from those previously proposed, which involve the formation and subsequent thermal decomposition of intermediate solid‐phase antimony oxychlorides, and demonstrate that the antimony compounds, rather than serving only as inert sources for SbCl3, readily participate in direct chemical reactions with HCl. In addition to the composition of the reaction products, information is also obtained on their evolution characteristics from the sample cell.

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