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The present work aims at investigating the relationship between the structural change and the electrical properties of isotactic polypropylene irradiated by gamma-rays at doses up to 100 kGy. Physicochemical analyses revealed a substantial increase of the carbonyl index of the material after irradiation along with a considerable increase of crystallinity which can be attributed to the cross-linking phenomenon. Dielectric properties of the materials were probed by charging/discharging currents and thermally stimulated currents. A significant increase in the conductivity was observed in comparison to the virgin sample. The thermally stimulated discharge current exhibits two peaks, whereas no peak was detected in virgin sample. These features appear related to the detrapping of space charges from deep traps created upon irradiation. [ABSTRACT FROM AUTHOR]

The purpose of this work is to describe, with numerical simulation, the space charge behavior in polymeric materials. Particular intent is accorded to the variation of the thermo-electrical constraints. The simulation is performed for a range of the electric field from 10 to 110 MV/m and the space charge behavior was described at various temperatures: 0, 27, 60 and 100 ° C. In general, the numerical results show a predominance of the temperature effect, vs. the electric field, on the space charge behavior. The dynamic of the electrical charges is different under 100 ° C, a forehead is observed on their distribution in the sample. Strong electric field enhancements are remarked in the dielectric, they exceed 38% of the applied field under 100 ° C. Only 1.3% of augmentations are observed under room temperature even with higher applied field of 110 MV/m. Both experimental and theoretical Current-Field characteristics, plotted in log-log scale, show linear behavior with slopes greater than one. The different values of slope indicate space charge limited conduction; a change is remarked at 40 MV/m which can defines the beginning of the high fields regime in the case of the studied polymer (Polyethylene Naphthalate). [ABSTRACT FROM PUBLISHER]

Abstract: This paper presents an experimental results obtained by using three investigation methods. The temperature effect on space charge behavior, in semi crystalline polyethylene naphthalate (PEN), under electrical strength, was analyzed. The Anomalous charging current, which is generally attributed to space charge, was observed. The non-isothermal current exhibited two peaks one located at 130 ∘C near the glass transition temperature , and the other, which was associated to pre-melting of crystallites, at 150 ∘C. The DSC analyze showed a at 128 ∘C and an endothermic peak at 150 ∘C. From these results it can be concluded that the trapped space charge can not release from the sample and requires an increase of temperature. Above , the molecular motion facilitates the de-trapping of the charge. [Copyright &y& Elsevier]

Abstract: Numerical simulation of transient discharge current passes along polyethylene naphthalate film was carried out from an experimental space charge distribution, obtained after charging process. This model showed good agreement with experimental current and allowed us to calculate space charge distribution and internal field. [Copyright &y& Elsevier]

The effect of temperature on transient electrical charging current in gold metallized polyethylene terephthalate (PET), which is a polymer of particular interest in electrical applications, was analyzed and compared with the results of previous work on aluminum metallized PET. Charging and discharging currents were measured with electrical fields ranging from 24 × 106 to 56 × 106 V/m and temperatures between 40° and 140°C. A model based on space charge formation was proposed. Simulated current showed good agreement with experimental current. This model allowed us to calculate space charge distribution and internal field. [ABSTRACT FROM AUTHOR]

Abstract: Polyethylene naphthalate (PEN) thin films were subjected to gamma rays at different doses and changes in both the dielectric and photophysical properties were investigated. Samples were irradiated in air at room temperature by means of a 60Co gamma source at a dose rate of approximately 31Gy/min. Total doses of 650kGy (344h) and 1023kGy (550h) were adopted in this work. The space charge profiles and residual electric field of virgin material and material exposed to these representative doses, obtained after 30min of depolarization following field application in the range 40–200kV/mm, have been examined by Focused Laser-Intensity Modulation Method (FLIMM). The dependence of space charge density with electric field values and irradiation dose is analyzed. Under high DC voltages and after irradiation, PEN tends to accumulate space charge. Space charge versus electric field and current-field characteristics issued from FLIMM method and conduction measurements exhibit good agreement. The high radiation resistance of PEN film is highlighted. [Copyright &y& Elsevier]