Oxidative degradation of polyvinyl alcohol by the photochemically enhanced Fenton reaction. Evidence for the formation of super-macromolecules

Abstract

The reaction mechanism of the oxidative degradation of polyvinyl alcohol (PVA) by the photochemically enhanced Fenton reaction has been studied. Fast and efficient degradation was observed in a batch reactor, using a medium pressure mercury arc in a Pyrex envelope and employing 80% of the stoichiometric amount of H2O2 required for the total oxidation of PVA and a concentration ratio as low as 1 mole of iron(II) sulfate per 20 moles of PVA sub-units (C2H4O). Model PVA polymers of three different molecular weights (15,000, 49,000 and 100,000 g mol-1) were found to follow identical degradation patterns. Strong experimental evidence supports the formation of super-macromolecules (MW: 1.5 × 106 g mol-1) consisting of oxidized PVA and trapped iron(III) at an early reaction stage. Low molecular weight intermediates, such as oxalic acid, formic acid or formaldehyde were not found during the PVA degradation, and we may deduce that the manifold of degradation reactions is mainly taking place within the super-macromolecules from which CO2 is directly released.