The Pyrolysis of Poly(vinyl chloride) Containing Phosphates

Abstract

The dehydrochlorination mechanism and flame retarding mechanism of poly(vinyl chloride) (PVC) containing sodium phosphates were studied by means of DTA, TG, X-ray diffraction, IR, ESR and gas analyses.The following results are obtained;1) HCI evolved from PVC reacts with sodium phosphates at about 210. v2500C except sodium hydrogen phosphate. The reaction products are sedium chloride and phosphoric a- D The formation of sodium chloride is largest and the evolution of hydrogen chloride is smallest in PVC containing sodium orthophosphate. Hence, sodium orthophosphate is most reactive against HCI among various phosphates.2) The fiame retarding effect of phosphates is attributed both to sodium hloride which is a stable salt against heat and has the flame retarding effect at high temperature due to its physical property, and to phosphoric acid which may inhibit PVC to burn on its surface due tg becoming vitreous poly(metaphosphoric) acid which suppresses a good supply of oxygen that covers PVC.3) Furthermore, the gas phase combustion may be also suppressed, since PVC which is covered with vitreous rrtetaphosphori acid burns only incompletely and produces non com b-ustible gas, fer example, carbon dioxide and arematic compounds. On the other hand, PVC alone produces combustible gas (low hydrocarbons) during c6mbustion. This fact is elucidated in the following table by indicating the ignition temperature and the activatibn energies for PVC containing phosphates.4) The stability against heat is confirmed by the following results based on IR and ESR analysesa) IR absorpticn bands of C O and C Care not observed at 240 C in PVC containing phosphates, while these bands are observed at the same temperature in PVC alone, b) The temperature at which the ESR signal of polyenyl radical appears for PVC containing phosphates is higher than that for PVC alone. The evolution of polyenyl radical is suppressed in the case of PVC eontaining phosphates.