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Biaxially oriented polypropylene (BOPP) film is a mainstream dielectric material used in power capacitor, there is still a large gap between thermal stability performance of imported BOPP films and that of domestic films. In order to systematically investigate the thermal stability of domestic and imported BOPP film, as well as to reveal the thermal ageing mechanism, we selected typical domestic and imported BOPP film samples, and conducted vacuum thermal ageing test on them for 1 000 h under 80℃ and 120℃, respectively. The changing law of molecular structure, aggregation structure, and electrical properties of the films before and after thermal ageing was compared and analyzed via infrared spectroscopy (FTIR), optical microscope observation, X-ray diffraction (XRD), dynamic thermomechanical analysis (DMA), dielectric spectroscopy, and direct current breakdown strength. The results show that compared with that of imported BOPP films, the crystallinity of domestic films is lower and the force between molecular chains is weaker. The breakdown field strength of domestic films is 5.7% lower than that of imported films. Under the effect of long-term thermal ageing, both BOPP films have undergone recrystallization, including the increase of crystallinity and lamellae size in the crystal region and the increase of free volume and the molecular chains loss scale in the amorphous region. Meanwhile, the change of the aggregate structure leads to the increase of the dielectric loss and the decrease of the breakdown strength at low probability zone of the film after ageing. Moreover, compared with domestic films, the stronger inter-chain forces in imported films effectively inhibit the recrystallization process, and decrease the generation and development of electrical weakness, which makes the imported BOPP films have better long-term thermal stability.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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