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The present work investigates the effects of photo-oxidation under accelerated UV conditions on the structure, the molecular weight and the morphology of polystyrene (PS)/organophilic montmorillonite (OMMT) at various clay contents: 2.5, 5, and 7 wt %. Fourier transform infrared spectroscopy, viscosimetry and scanning electron microscopy were used to evaluate the extent of degradation of nanocomposite samples in comparison with neat PS, up to 216 h of exposure. The study has shown that the formation rates of both carbonyl and hydroperoxide groups increase with exposure time, being much higher for PS/OMMT nanocomposites. Moreover, it is also observed that all samples exhibit a large increase in the scission index, however less pronounced for neat PS. These results clearly indicate the formation of low molecular weight products that could arise from chain scission. Further, the photo-oxidation rate seems to be more affected by the presence of clay, which acts as a catalyst, rather than by the variation of clay contents. Finally, the degraded materials exhibit eroded surface.

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The effect of gamma‐irradiation on the structure, rheology, and mechanical properties of low density polyethylene (LDPE) films containing some new hindered amine stabilizers (HAS) has been investigated and the results obtained were compared to additive free samples. The HAS used involved various structures such as an alkoxyamine, a polymer bound HAS and a HAS modified with siloxane; these are commercially known as Tinuvin 123, Sanduvor PR 31 and Uvasil 299, respectively. It was found that the carbonyl index values measured by FTIR spectroscopy increased linearly with the radiation dose for all the samples studied, however this increase was less pronounced for the stabilized samples. The formation rates of carbonyls followed the order LDPE > LDPE/Uvasil 299 > LDPE/PR 31 > LDPE/Tinuvin 123. The second order derivative UV analysis showed the formation of vinyl groups in the irradiated samples at higher doses (812 kGy), while vinylidene groups were detected only in the films stabilized with PR 31 and Tinuvin 123. The curves of the melt flow rate (MFR) exhibited a fast increase for the unstabilized sample after 67 kGy, indicating the occurrence of chain scission. The stabilized samples on the other hand showed an evident increase in MFR from almost 300 kGy. The contribution of different HAS for the durability of LDPE films under γ rays was evaluated by determining the half‐value‐dose, which is related to the radiation resistance of the material. The results indicated that the presence of HAS in LDPE films improves the half‐value‐dose of those stabilized with Tinuvin 123 by 2.5 times against 2.4 and 2 for PR 31 and Uvasil 299, respectively. These data correlate well with the results obtained by FTIR and MFR measurements. Finally, the higher efficiency of Tinuvin 123 could be assigned to its appropriate oxidation state to enter the stabilization mechanism directly.An example of the new HAS.magnified imageAn example of the new HAS.

Summary: The thermal stability of gamma irradiated low density polyethylene (LDPE) films in presence of various structures of hindered amine stabilizers (HAS) was investigated by the oxygen uptake method under constant temperature of 180 °C and normal pressure conditions. The thermo‐oxidation was run using air environment. The sigmoidal dependency of oxygen uptake allows the calculation of the main kinetic parameters: oxidation induction time and oxidation rate on the propagation step. The various steps involved in the thermal degradation process were detected by the derivative procedure applied to the dependencies of oxygen uptake on time. It was found that the kinetic parameters of the thermal degradation process, determined by oxygen uptake, revealed the antioxidant role of HAS in γ‐irradiated LDPE films by providing better stability, when compared with the unstabilized samples. Moreover, the results indicated that the dependencies of oxygen uptake on thermal degradation time involved two degradation stages: the former occurring in the ungrafted moiety and the latter taking place after the antioxidant depletion is achieved. The stabilization efficiency of these oxidation inhibitors provides satisfactory thermal resistance to LDPE films, especially those based on an alkoxyamine structure.Dependencies of oxygen uptake on time at the thermal degradation of LDPE irradiated at 812 kGy. (‐□‐) free of additive; (‐○‐) Tinuvin 123; (‐▵‐) Sanduvor PR 31; (‐⋄‐) Uvasil 299.magnified imageDependencies of oxygen uptake on time at the thermal degradation of LDPE irradiated at 812 kGy. (‐□‐) free of additive; (‐○‐) Tinuvin 123; (‐▵‐) Sanduvor PR 31; (‐⋄‐) Uvasil 299.