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Gardette M.,Institute of Chemistry of Clermont-Ferrand | Perthue A.,Institute of Chemistry of Clermont-Ferrand | Gardette J.-L.,Institute of Chemistry of Clermont-Ferrand | Janecska T.,Tisza Chemical Group Public Ltd Company TVK | And 5 more authors.
Polymer Degradation and Stability | Year: 2013

The behaviour of polyethylene with different contents in vinyl and t-vinylene groups have been studied by photooxidation with λ ≥ 300 nm light or by thermooxidation at a temperature of 100 C. The oxidation was studied by infrared spectroscopy and it was shown that the same oxidation products were obtained, but with different relative concentrations depending on the conditions of ageing, i.e. photochemical or thermal conditions. The mechanisms by which the oxidation products are formed were recalled. The differences between photo- and thermo-oxidation were evidenced on the basis of the stability of ketones that do not accumulate in photochemical conditions, as a result of Norrish reactions. The influence of the initial amount of unsaturated groups on the rates of oxidation was characterized. It was shown that the concentration of unsaturations had no effect on the rate of photooxidation but dramatically influenced the stability in thermooxidative conditions. © 2013 Elsevier Ltd. All rights reserved. Source

Tatraaljai D.,Hungarian Academy of Sciences | Tatraaljai D.,Budapest University of Technology and Economics | Vamos M.,Hungarian Academy of Sciences | Vamos M.,Budapest University of Technology and Economics | And 6 more authors.
Polymer Degradation and Stability | Year: 2014

Polyethylene (PE) compounds were prepared with five primary antioxidants and five application stabilizers, pelletized and extruded to pipes under industrial conditions. The pipes were stored in water at 80 C for one year. Samples were taken at various intervals and a range of properties were determined from the functional group (methyl, vinyl, t-vinylene) content of the polymer to the crack propagation rate of the pipe. The results showed that chemical reactions take place both during extrusion and soaking. The chain structure of the polymer is modified only during processing, but not during storage, at least in the time scale of the study. The direction and extent of changes are determined mainly by the type of the application stabilizer, but primary antioxidants also influence them to some extent. Soaking modifies the physical, but not the chemical structure of the polymer. On the other hand, the chemical reactions of the additives determine color and stabilizer loss thus the residual stability of the pipes. The chemical structure of the polymer has a larger effect on final properties, on the rate of slow crack propagation and failure, than the physical structure of the pipes. As a consequence, the application stabilizer plays an important role in the determination of pipe performance. © 2013 Elsevier Ltd. All rights reserved. Source

Kovacs J.,Hungarian Academy of Sciences | Kovacs J.,Budapest University of Technology and Economics | Pataki P.,Hungarian Academy of Sciences | Pataki P.,Budapest University of Technology and Economics | And 7 more authors.
Polymer Degradation and Stability | Year: 2011

Different aspects of the melt stabilising effect of various antioxidant packages were studied in a Phillips type polyethylene in the work described in this series of papers. The polymer was stabilised with various combinations of a phenolic antioxidant with phosphite, phosphonite, and phosphine type secondary antioxidants and processed by multiple extrusions followed by film blowing. After determining the role of the antioxidants in the melt stabilisation process and the effect of antioxidant consumption on polymer properties the correlation of the rheological characteristics of polymer with the tear and impact strengths of films is discussed in this paper. The Elmendorf tear strength of films measured in transverse direction, which is sensitive to long chain branching, correlates closely with viscous compliance determined by creep recovery experiments and the ratio of melt flow indices measured at high and low loads. The relationships are independent of the type and amount of antioxidant added. This makes possible the prediction of the effect of various antioxidant packages on film properties on the basis of rheological measurements. The correlation between the dart drop impact strength of the films and the rheological characteristics of the polymer is less reliable. © 2011 Elsevier Ltd. All rights reserved. Source

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