Combustion of poly(Vinyl chloride) studied by the moving wire technique

Abstract

This paper is a demonstration of the utility of the Moving Wire Technique (MWT) for studying polymer pyrolysis, ignition and burning. The polymer is coated on a support wire and transported at a uniform and controlled speed through a heat or ignition source flame. An advantage of the MWT is that residence time, as seen by an observer moving with the wire, is resolved spatially in laboratory coordinates (residence time is the ratio of distance to wire speed). This allows greater precision in measurements of composition and temperature profiles and makes it easy to obtain smaples of the solid phase. In this study, we compared reagent and commercial grade poly(vinyl chloride) (PVC). Our heat source was the wake of a flat CH4−O2−N2 flame. Excess O2 for polymer combustion was a part of the flame gases in some experiments but was confined to an adjoining flowing “atmosphere” in others. Ignition in an O2-rich source flame required a minimum of about 20% excess O2. Above this value, the O2-level had no effect on the critical surface temperatures at ignition, which were 295±5°C for the pure PVC and 370±10°C for two different brands of commercial PVC. Earlier studies with the MWT indicated that critical ignition temperatures appear to be independent of the diameter and heat capacity of the support wire, and the thickness of the polymer coating. Ignition occurred at the first appearance of flammable gas, identified as principally benzene in pyrolysis experiments. Reagent PVC emitted HCl prior to ignition but the commercial PVC did not. Quenched samples of the solid phase were collected for analysis; the quenching was accomplished by rapid cooling with cold He. A long-lived free radical was detected in the burned PVC, which was charred.