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Effects <strong>of</strong> Electron Beam Irradiation on Properties ... Park E-S Tensile Test Procedure Tube type specimens for mechanical tests were prepared in accordance with IEC 60811-1-1 [22] specification. The sample <strong>of</strong> wire was cut into pieces approximately 100 mm long and the conductor was removed by careful rolling <strong>of</strong> the wire under low mechanical force. The test specimens were preconditioned to 20% relative humidity and 20 ± 1°C in order to standardize test conditions. Tensile properties <strong>of</strong> the samples were determined with a universal test machine (UTM, Model DECMC00, Dawha Test Machine, Korea) at a cross-head speed <strong>of</strong> 250 mm/min. The mean value <strong>of</strong> at least five specimens <strong>of</strong> each sample was taken, although the specimens that broke in an unusual manner were disregarded. Scrape Abrasion Resistance Test Scrape abrasion resistance was measured using an Abrasion Tester (Core Tech, Korea). The test pieces were 750 mm <strong>of</strong> extruded wire in length and they were prepared by EB <strong>irradiation</strong>. The travel distance <strong>of</strong> specimen was 10 mm at a speed <strong>of</strong> 60 cycles per minute and the test loads were 5 N and 10 N. The abrasive used was a needle (material: tungsten carbide, diameter: 4.5 mm, knife: 4.5 mm × 1 mm). Each specimen underwent five tests and was moved about 100 mm between each test and turned at an angle <strong>of</strong> 90°, always in the same direction. A wire sample was fixed to the sample holder and 24 V direct current (DC) voltage was applied between abrasive and wire conductor. When electric contact occurred between abrasive and conductor, test equipment stopped running and the cycles at breakdown were automatically counted. ETFE ETFE-01 ETFE-05 ETFE-10 ETFE-15 ETFE-20 876 Sample code No crack No crack No crack No crack No crack No crack Iranian Polymer Journal / Volume 20 Number 11 (2011) Flexibility Test A straight piece <strong>of</strong> 300 mm wire was carefully wound in 10 continuous adjacent turns around a polished mandrel <strong>of</strong> 60 mm diameter. The specimen was placed into an oven with forced air circulation at room temperature or 240°C for 30 min. After removal from the oven, the specimen was allowed to cool to room temperature. After cooling the thermally aged wire was straightened and was examined for cracks under a video microscope. Breakdown Voltage Measurement The measurements <strong>of</strong> breakdown voltage (BDV) were carried out at 60 Hz alternating current (AC) voltage by using a high voltage tester (SM-40PT08, Sungmin Instruments, Korea) with a rate <strong>of</strong> 0.5 kV/s in air. The test sample consisted <strong>of</strong> copper conductor (diameter <strong>of</strong> 2 mm) and outer insulator (insulation thickness <strong>of</strong> 1 mm). Before conducting the BDV test, an aluminium foil was wrapped around the outer surface <strong>of</strong> the wire. An AC voltage was applied between the aluminium wrap and the wire conductor and a dielectric BDV was measured. Ten samples were tested and the average voltage was calculated. RESULTS AND DISCUSSION Table 3. Insulation properties <strong>of</strong> the EB-irradiated wire before and after flexibility test. BDV and ρ I Changes <strong>of</strong> Extruded Wire after EB Irradiation The ETFE insulated wire was subjected to EB <strong>irradiation</strong> (1 to 20 Mrad) and the BDV measurement results <strong>of</strong> the EB-irradiated samples are summarized in Table 3 (left part). The abbreviation <strong>of</strong> the sample code in Table 3, ETFE-01, for example, means that EB <strong>irradiation</strong> Thermal aging at 240°C for 30 min Flexibility BDV (kV) Flexibility BDV (kV) 21.6 ± 0.6 21.3 ± 0.6 20.9 ± 1.1 20.5 ± 1.4 18.7 ± 0.5 16.8 ± 1.9 No crack No crack No crack No crack No crack No crack 21.5 ± 1.3 18.8 ± 2.6 17.8 ± 0.8 16.8 ± 5.0 16.3 ± 5.6 14.0 ± 3.1
Park E-S the ETFE insulated wire was EB-irradiated at 1 Mrad. The BDV <strong>of</strong> ETFE-01, ETFE-05 and ETFE- 10 were slightly changed compared with pristine ETFE. In sharp contrast BDV <strong>of</strong> ETFE-15 and ETFE- 20 were decreased significantly. Approximately 13% and 22% decreases were observed in BDV <strong>of</strong> 18.7 and 16.8 kV, respectively. The dielectric breakdown causes a high-temperature arc to propagate through a Effects <strong>of</strong> Electron Beam Irradiation on Properties ... (a) (d) (b) (e) (c) (f) Figure 1. Images <strong>of</strong> the breakdown points after dielectric breakdown test (200x). dielectric medium and these can lead to ignition <strong>of</strong> the medium or <strong>of</strong> the surrounding objects. Figure 1 demonstrates the breakdown points after dielectric breakdown test. As the <strong>irradiation</strong> dose increased, the char formation and size <strong>of</strong> breakdown point were decreased significantly (above 10 Mrad). This means that the breakdown <strong>of</strong> EB-irradiated wire is determined by the electrical field at the tip <strong>of</strong> the defect. Iranian Polymer Journal / Volume 20 Number 11 (2011) 877
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Page 7 and 8: Park E-S CH 2 CH 2 CH 2 CH 2 CH CH
Page 9 and 10: Figure 5. TGA Thermograms o
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