Thermal and photo-chemical oxidation of poly(vinyl chloride): Implication of α,β-unsaturated carbonyl groups

Abstract

The thermal and photo-chemical oxidation of poly(vinyl chloride) film has been studied under the same conditions using second-order derivative uv and fluorescence spectroscopy and hydroperoxide analysis. Four absorption bands are observed to undergo changes. The first, at 210 nm, associated with a single vinyl group, is unstable and disappears rapidly on thermal treatment. The second, at 230 nm, increases rapidly, as does a fourth small band in the near uv at 325 nm, and is concurrent with the growth in a new fluorescent product which is attributed to an α,β-unsaturated carbonyl group. The third, at 275 nm, increases at a low linear rate during thermal oxidation but at a catalytic rate during photo-chemical oxidation, and is associated with aliphatic ketonic/aldehydic groups. Hydroperoxides are also produced at a linear rate during thermal oxidation but do not match the carbonyl growth photo-chemically. Only the fluorescent oxidation product appears to match closely the autocatalytic rate of carbonyl production photo-chemically. However, even here, a contribution from hydroperoxide initiation is evident and this is probably the major initiator in mildly processed material.