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中文摘要：
聚酰亚胺薄膜因其优良的电气、机械及热性能已在各种绝缘线缆中得到广泛应用。然而,环境应力可能会造成聚酰亚胺降解,从而降低其绝缘性能。以聚酰亚胺普通薄膜和聚酰亚胺纳米薄膜为测试对象,研究了单层膜、双层膜及三层膜在不同温度下的击穿特性,分析了水分对聚酰亚胺薄膜击穿场强的影响机制。结果表明：普通膜和纳米膜的击穿强度均随试验温度的升高而降低,尤其是当试验温度大于350℃时,下降速率明显增加,其主要原因是由于聚酰亚胺分子在高温下移动并发生热降解。由于单层膜具有更好的散热能力及结构均匀性,因此单层膜具有比双层膜和三层膜更高的击穿场强,纳米膜较高的热导率导致其具有更好的高温稳定性。潮湿环境中的水分子首先通过氢键作用与聚酰亚胺分子上的羧基（C=O）键结合,并进一步与之发生水解反应,使聚酰亚胺薄膜的击穿场强降低。
英文摘要：
Polyimide（PI） film has been widely applied as electrical insulation for wires and cables due to its excellent electrical, mechanical and thermal properties. However, PI insulation could be degraded because of various environmental stresses, which can cause deterioration of their insulation properties. In this paper, the effects of thermal exposure on dielectric strength of nanocomposite PI film and pure PI film were investigated. The comparison of the breakdown field strength of single layer film, double layer films and three layer films were also studied. The influence mechanism of humidity on the breakdown strength was analyzed. The results show that the breakdown field strength of PI films, both nanocomposite PI film and pure PI film, is greatly decreased with the tested temperature increasing. And the decreasing rate of breakdown field strength increases more obviously when the tested temperature is more than 350 ℃. It is due to the motion and pyrolysis degradation of PI macromolecules caused by overheating. The single film possesses better heat dissipation potential and homogeneous micro-structure. Therefore the breakdown field strength of single layer film is higher than those of double layer films and three layer films. Higher thermal conductivity of nanocomposite PI film has the better breakdown stability in high temperature environment. Some hydrogen bonds exist between water molecule and carboxyl in the backbone chain of PI polymer. The hydrolysis reaction of PI macromolecule would make the dielectric strength of PI film decrease.
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