Condensed Phase Mechanism of Phosphorus Flame Retardarscy in Polymers

摘要

A condensed phase mechanism by which phosphorus imparts flame retardancy to polymers is proposed. The mechanism is modeled as a chemical kinetic process in which organic phosphorus compounds RPOx hydrolyze to phosphoric acid, which catalyzes the dehydration of hydroxyl-containing compounds to form char, water, and fuel gases. The relative rates of P-catalyzed and non-P-catalyzed (homogeneous) charring are obtained from a single-parameter fit of the kinetic solution to experimental data for char yield versus phosphorus concentration. The results' show that the molar charring efficiency of phosphorus increases as the number of P-O bonds in the starting compound, i.e., P < PO < PO2 < PO3 < PO4. The observed gas phase activity for RPOx for x < 2 and condensed phase activity (charring) for x > 2 may simply be a consequence of the solid state kinetics.