The photo-oxidation of polypropylene/montmorillonite nanocomposites has been studied under irradiation at long wavelengths (λ > 300 nm) at 60 °C and in the presence of oxygen. The chemical modifications resulting from photo-oxidation were followed by IR and UVvisible spectroscopies for each component of these nanocomposites polypropylene (PP), organomodified montmorillonite (MMt), and the compatibilizing agent (maleic anhydride-graftedpolypropylene). We have found that the mechanism of photo-oxidation of the polypropylene component was not modified in the polymer-nanocomposite, but that the rates of oxidation were modified, leading to an unexpected decrease of the durability of the material.

Summary: The degradation of an epoxy/amine resin was studied under photolytic conditions in absence and in presence of oxygen and under thermooxidative conditions. The resin is obtained after curing the diglycidyl ether of bisphenol‐A (DGEBA) with a poly(propylene glycol) which is diamine terminated. The mechanisms of degradation of the two separate components before curing were also investigated. Analysis by IR and UV‐Vis spectroscopies revealed that the oxidation photoproducts detected during the degradation of the epoxy/amine result from the oxidation of the DGEBA part, of the amine crosslinks and, to a lower extent, of the poly(oxypropylene) units. Their mechanism of formation essentially involves chain scission reactions. During irradiation, the yellowing observed is mainly due to the formation of a quinone methide structure. Thermooxidation generates high discoloration with some products only generated in that case. For all experiments, a detailed analysis of the IR spectra is given with the chemical mechanisms of formation of the degradation products.ATR‐IR spectra of an epoxy/amine sample in the carbonyl region during photooxidation.magnified imageATR‐IR spectra of an epoxy/amine sample in the carbonyl region during photooxidation.

The influence of stabilizing additives on the photooxidation of polypropylene/montmorillonite (PP/ MMt) nanocomposites exposed to UV light was studied. Two different stabilizers were used, a phenolic antioxidant and a redox antioxidant. A significant reduction in the induction period of oxidation was observed in the presence of MMt. This is believed to arise from interactions between the additives and the nanoclay. The interactions could involve the adsorption of additives onto the clay, the degradation of the alkylammonium cations exchanged in MMt, and the catalytic effect of iron impurities of the organomontmorillonite. Iron could catalyze the decomposition of the primary hydroperoxides formed by photooxidation of PP, which would in turn accelerate the additive consumption and decrease the length of the period before the permanent regime of oxidation is reached.

This paper is devoted to the investigation of the phototransformation mechanisms of PVK exposed to long-wavelength radiations (λ > 300 nm) in the absence and in the presence of oxygen. PVK irradiated as thin films was analyzed by fluorescence, UV-vis, and IR spectroscopies. The photoproducts formed were identified by postirradiation treatments including chemical derivatization reactions and HPLC analysis. The cross-linking was evaluated by gel fraction measurements. PVK is known to give an intense excimer fluorescence and no monomer fluorescence. The phototransformations provoked by light absorption are shown to lead to a dramatic decrease of this fluorescence which can be correlated with the modification of the chemical structure of the macromolecules. The decrease of fluorescence is the result of the diminution of the local mobility of the macromolecular chains resulting from cross-linking reactions provoked by the recombination of the several radicalar species. A general mechanism accounting for the phototransformation of PVK in the presence and in the absence of oxygen is proposed.

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