The pyrolysis and nonflaming oxidative degradation of poly(vinylfluoride)

The thermal degradation of poly(vinylfluoride) (PVF) was studied under slow heating conditions to 1000°C with and without the presence of air. The degradation products, classified as low-boiling volatiles, high-boiling volatiles, and nonvolatile residues, were analyzed quantitatively by gas chromatography—mass spectrometry and several spectroscopic methods. Initial stages of degradation begin at 420°C with the evolution of HF and benzene and rapidly reach a maximum in sample weight loss by 450°C. One-third of this weight loss was in the form of hydrofluoric acid (HF) and at least 70 low-boiling volatile compounds that consisted of substituted aromatics, unsaturated hydrocarbons, and multiple-ring compounds, many of which contained a fluorine atom. The high-boiling volatile fraction contained compounds with more aliphatic but less aromatic character than the low-boiling. The nonvolatile residue retained 4% of the original fluorine content and exhibited strong unsaturated character. In the presence of oxygen HF, CO, and H₂O were the major constituents of the low-boiling volatiles; the organic fraction was essentially unchanged in composition but reduced in overall concentration. The overall weight-loss process was bimodal in air and produced a thermally resistant residue that degraded by 650°C. A comparison of degradation products from poly(vinylchloride) with this work demonstrates that PVF forms more lower-molecular-weight, halogen-containing compounds, whereas the former produced more HCl and nonvolatile residue containing a lower halogen content.