The formation of volatile pyrolyzates form poly(vinyl chloride)

Abstract

SynopsisThe formation of volatile pyrolyzates in poly(viny1 chloride) has been studied by pyrolysis-gas chromatography-mass spectroscopy. Isotopic distributions of pyrolyzates from experiments with perdeutero-PVC show that pure conjugated aromatic pyrolyzates (e.g., benzene, styrene, naphthalene, biphenyl, anthracene) are formed mostly via intramolecular cyclization. Mixed aromatic-aliphatic pyrolyzates (e.g., toluene, indene, methylnaphthalene) are formed at least partially via intermolecular (crosslinking and/or hydrogen transfer) mechanisms. Direct scission of the PVC chain to form chlorine-containing pyrolyzates is a very minor degradation pathway. Most chlorine-containing "pyrolyzates" from PVC are due to secondary reactions of HCl with the environment or with non-PVC compounding ingredients. No evidence was found for oxygen-containing pyrolyzates derived from the PVC backbone under conditions of nonflaming pyrolysis in air.

Semivolatile and volatile compounds from the pyrolysis and combustion of polyvinyl chloride

“…Benzene, which is a carcinogenic compound, is one of the main products resulting from the thermal degradation of PVC [3][4][5]. Other substituted monoaromatic and polyaromatic hydrocarbons (PAHs) are reported to appear in pyrolysis and combustion of PVC at different temperature ranges [5][6][7][8][9][10][11][12][13].…”

“…Lattimer and Kroenke [3] reported that direct scission of PVC chains to form chlorinated-containing compounds is a very minor decomposition pathway because an inappreciable amount of chlorine remains in the polyene after dehydrochlorination. However, McNeill et al [19] suggested the possibility of a small-scale readdition of HCl or Cl 2 to polyenes after dehydrochlorination in the vicinity of head-to-head defects already containing chlorine atoms to create zones of high Cl concentration that can eventually lead to chlorinated aromatics such as PCDD/PCDFs.…”

“…The different behavior can be explained taking into account that methane is a final product from cracking reactions occurring at high temperatures, while benzene is known to be a primary decomposition product from thermal decomposition of PVC [3][4][5] and also has a great thermal stability [38]. On the other hand, types A 0 and I behaviors are almost general, that indicates that the combination of oxygen and high temperatures significantly depletes formation of light hydrocarbons.…”

“…According to some authors [3][4][5], PVC thermal degradation consists of two main steps: hydrogen chloride is firstly released and then, aromatic hydrocarbons are subsequently formed from cyclization reactions of the remaining polyene chain and also a residual char is generated. The presence of oxygen in the atmosphere instead of an inert gas allows the char to volatilize completely.…”

Analysis and structure prediction of chlorinated polycyclic aromatic hydrocarbons released from combustion of polyvinylchloride

“…Cl-PAHs detected in these tests are mainly derivatives of naphthalene, phenanthrene, anthracene, biphenyl, fluorene and pyrene. These chlorinated derivatives might be formed mainly by chlorination reaction of the PAHs with chlorine released from PVC combustion, because direct scission of PVC chains to form chlorine-containing compounds is a very minor decomposition pathway (Lattimer and Kroenke, 1980). Furnace temperature, airflow, the burning time and the combustion duration have an effect on the levels of Cl-PAHs in the emissions from PVC combustion.…”