96_Laurennt_influence_UV_Thermal - IEEE Transacfionson...

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148 IEEE Transacfions on Dielechics and Electrical Insulafian Vol. 3 No. 1, February 1996 Influence of Thermal and UV Aging on Electroluminescence Polypropylene Films J. Jonsson, B. RAnby Department of Polymer Technology, Royal Institute Technology, Stockholm, Sweden G, Laurent and C. Mayoux Laboratoire de Genie Electrique, Universite Paul Sabatier, Toulouse, France ABSTRACT Polymer aging appears to be an important factor which affects the electrolumines- cence of polyolefins subjected to a homogeneous ac field. We investigate the influ- ence on electroluminescence emission of thermal and UV aging of commercial pol- ypropylene films for capacitor application. Chemical and morphological changes of the materials are studied as function aging conditions. Correlation is found be- tween material oxidation and electroluminescence. Oxidation reduces the level of electroluminescence but does not change the spectral distribution of the light, there- by indicating that the luminescence centers are not the carbonyl groups. 1. INTRODUCTION NE of the phenomena reported to occur when a polymer is submitted to an ac voltage is electroluminescence (EL). EL is not due to discharges but is dependent on the material and on the voltage applied to it. It has been associated with electrical ag- ing of the material and could be used to monitor dielectric aging EL of polymers is currently poorly understood. The nature of the luminescence centers and the excitation mechanisms are con- troversial. Most experiments have been performed using nee- dle samples, but some recent results deal with thin films 141. Us- ing polymer films under a uniform field provides means to study the material parameters which influence the emission, e.g. chemi- cal formulation, concentration of given chemical groups, polymer microstructure, or material aging. In earlier studies, the EL emission has been shown to decrease both with increasing carbonyl content in the main chain of poly- ethylene films [4], and after electrical aging of an XLPE cable 151. An increasing carbonyl group content is likely to occur when a polymer material is aged and often is used as a probe to monitor aging of a material. A method widely used to accelerate aging for polymer materials is to subject the films to LJV or to raise the temperature to increase the speed of the chemical reactions. In this study, thin polypropylene (PP) films have been exposed to at 53°C for times spanning from 0.5 to 71 h. Thermal aging also has been performed at different temperatures up to 160°C. Several methods have been used to measure the chemical and 11- 31. morphologcal changes of the materials during aging. Electrolu- minescence measurements were carried out on these films in an attempt to unravel the possible influence of aging on light inten- sity and spectral features.
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This note was uploaded on 06/11/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.

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96_Laurennt_influence_UV_Thermal - IEEE Transacfionson...

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