Investigations on poly(vinyl chloride). I. Evolution of aromatics on pyrolysis of poly(vinyl chloride) and its mechanism

Poly(vinyl chloride) (PVC) alone or mixed with 10 wt-% and 50 wt-% TiO₂, SnO₂, ZnO, and Al₂O₃ were pyrolyzed by using a pyrolysis gas chromatograph. Benzene, toluene, ethylbenzene, o-xylene, styrene, naphthalene, and various chlorobenzenes were identified. No hydrocarbons could be detected in pyrolysis products of any samples at 200°C. More aromatic hydrocarbons than aliphatic hydrocarbons are released from the PVC–TiO₂ system and in preheated PVC. The contrary result is observed in the PVC–ZnO and PVC–SnO₂ systems. Aromatics having methyl endgroups are easily released from the PVC–ZnO and PVC–SnO₂ systems and at elevated pyrolysis temperature, because methylene groups are easily isolated along the chain by ZnO, SnO₂ and the heating. The release of ethylbenzene o-xylene, and chlorobenzenes suggests a repeated dehydrochlorination and recombination of HCl and Cl₂ to double bonds along the chain. Possible decomposition mechanisms of PVC are discussed.