The conduction of nonoriented, hazy polypropylene films has been investigated between 8 degrees C and 123 degrees C at electrical stresses of up to 20 kV DC using a ramping speed of 200 V/s and an inert atmosphere. The film thickness ranged from 70 to 80 mu m. The recorded current traces indicate unusual behavior in the vicinity of 113 degrees C. High-resolution differential scanning calorimetry also suggested a departure from linear behavior at this temperature. An attempt is made to explain this behavior in terms of structural changes that lead to the development of a negative resistance.
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