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Epoxy resin is widely used in the field of motor insulation. The researchers has conducted considerable research on its macroscopic performance changes under thermal oxidative ageing conditions, but the research on the ageing at molecular structure level ageing is limited. This paper systematically investigated the changes in chromophore groups, free radical content, cross-linking network functional groups, and internal micro-defects of epoxy resin samples under different thermal oxidative ageing time using ultraviolet spectroscopy, electron paramagnetic resonance spectroscopy, infrared spectroscopy, and two-dimensional X-ray scattering. The results show that after thermal oxidative ageing, the samples exhibit distinct absorption peaks at ultraviolet wavelengths of 406 nm (corresponding to p-benzoquinone) and 636 nm (corresponding to dibenzoquinone or naphthoquinone derivatives), and the appearance of the samples turns dark brown. The free radical content increases rapidly with ageing time (reaching a high level at 20 h) then gradually decreases, and maintains a low level after 80 h. The destruction of cross-linking network functional groups follows a specific sequence with the increase of thermal oxidative ageing time, and the destruction rate of functional group slows down after 80 h. There are micro-defects inside the sample, and the defect size gradually increases with the increase of thermal oxidative ageing time.
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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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