Effects of pressure on the degradation of poly(vinyl chloride)

Poly(vinyl chloride) was decomposed for 0-90 min at 300-440°C under 0-6.0 MPa of nitrogen pressure. Hydrogen chloride, liquid products, and residue were the main decomposition products. The yield of liquid products decreased with increasing reaction pressure, whereas the yield of residue increased, reaching maxima at 9.8 MPa (400°C) and 22.4 MPa (440°C). The pressure dependences of the product distribution and atomic ratio of hydrogen to carbon (H/C) imply that some of the liquid products were polycondensed with the dehydrochlorinated PVC and were retained in the residue under high-pressure. At atmospheric pressure, benzene was the predominant product. The yield of benzene decreased sharply with pressure, whereas the yield of linear paraffins increased significantly. The liquid product distribution suggests that polyene chains in the dehydrochlorinated PVC were converted to benzene and alkylbenzene under atmospheric pressure. However, some of the polyene chains underwent hydrogenation to form linear paraffins under high pressure.