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Epoxy resin is widely used as a polymeric insulating material in power equipment, such as gas-insulated switchgear and gas-insulated lines. The motions of molecular chains or segmental chains in a polymeric insulating material can affect the material properties, such as dielectric relaxation, charge transport, breakdown, and glass transition temperature. Molecular or segmental chains may form dipoles, and their motions can contribute to dielectric relaxation properties. Molecular or segmental chains with different scales have different relaxation time constants. Their motions affect dielectric relaxation processes in different frequency ranges. The motions of molecular or segmental chains are also affected by temperature, since the magnitudes of motions are restricted by free volume in a polymeric insulating material. However, the effects of motions of molecular or segmental chains in epoxy resin on electrical properties have not been very clear to date. Therefore, it is important to investigate the relations between the motion of molecular or segmental chains and dielectric relaxation properties, the temperature and molecular scale dependence of the motions, and their effects on charge transport of epoxy resin. In this paper, the properties of dielectric relaxation and glass transition of epoxy resin are measured. Before the experimental tests, samples of pure epoxy resin are prepared by using epoxy raw materials supplied by Pinggao Group, and the curing temperature is 130 ℃. The glass transition temperature is around 105 ℃ measured by a differential scanning calorimetry (DSC). As for the dielectric relaxation measurement with Novocontrol broadband dielectric relaxation spectroscopy, the sample is processed into a disk with a diameter of 50 mm and a thickness of 1 mm. The measurement temperature and frequency are in ranges of 100-180 ℃ and 10-1-107 Hz, respectively. The results reveal that there are two relaxation processes at high temperature. In addition, above glass transition temperature, a relaxation peak occurs at high frequencies due to the motions of molecular chains or segmental chains, and a direct current (DC) conductivity resulting from the migration of charge carriers appears at low frequencies. Besides, molecular chains with different scales have different relaxation times. It is found that epoxy resin has a very broad distribution of relaxation times. The distributions of relaxation times at various temperatures are calculated. The results show that the temperature dependence of molecular relaxation and DC conductivity satisfy Vogel-Tammann-Fulcher equation. Through fitting the experimental results, the Vogel temperatures and strength parameters of molecular relaxation and DC conductivity are obtained. From the Vogel temperatures, the glass transition temperature is estimated to be 102 ℃, which is consistent with the DSC result. It means that free volume in epoxy resin increases with the increase of temperature, which facilitates the motions of molecular chains and the migration of charge carriers.
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Keywords:
- epoxy resin /
- dielectric spectrum /
- glass transition /
- relaxation properties
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[16] Badawia A, Al-Hosiny N 2015 Chin. Phys. B 24 105101
[17] Li S T, Yin G L, Bai S N, Li J Y 2011 IEEE Trans. Dielectr. Electr. Insul. 18 1535
[18] Min D M, Li S T, Hirai N, Ohki Y 2015 Proceedings of the 46th Symposium on Electrical and Electronic Insulating Materials and Applications in Systems Kyushu, Japan, September 4-6, 2015 p39
[19] He M J, Chen W X, Dong X X 1990 Polymer Physics (Shanghai: Fudan University Press) p224 (in Chinese) [何曼君, 陈维孝, 董西侠 1990 高分子物理 (上海: 复旦大学出版社) 第224]
[20] Alvarez F, Alegría A, Colmenero J 1991 Phys. Rev. B 44 7306
[21] Angell C A 1997 Polymer 38 6261
[22] Dudowicz J, Freed K F, Douglas J F 2005 J. Phys. Chem. B 109 21285
[23] Schönhals A, Kremer F, Hofmann A, Fischer E W, Schlosser E 1993 Phys. Rev. Lett. 70 3459
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[1] Liu Y Q, An Z L, Cang J, Zhang Y W, Zheng F H 2012 Acta Phys. Sin. 61 158201 (in Chinese) [刘亚强, 安振连, 仓俊, 张冶文, 郑飞虎 2012 61 158201]
[2] Wang X F 2009 Fundamentals of Electrical Engineering (Xi'an: Xi'an Jiaotong University Press) p20 (in Chinese) [王锡凡 2009 电气工程基础 (西安: 西安交通大学出版社) 第20页]
[3] Dang Z M, Wang H Y, Peng B, Lei Q Q 2006 Proc. CSEE 26 100 (in Chinese) [党智敏, 王海燕, 彭勃, 雷清泉 2006 电机工程学报 26 100]
[4] Huang X Y, Jiang P K, Jin T X, Ke Q Q 2007 Prog. Chem. 19 1776 (in Chinese) [黄兴溢, 江平开, 金天雄, 柯清泉 2007 化学进展 19 1776]
[5] De L A, Grando L, Pesce A, Bettini P, Specogna R 2009 Trans. Dielectr. Electr. Insul. 16 77
[6] Tenbohlem S, Schrocher G 2000 IEEE Trans. Dielectr. Electr. Insul. 7 241
[7] Jun X, Chalmers I D 1997 J. Phys. D: Appl. Phys. 30 1055
[8] Jin W F 1997 Dielectric Physics (Beijing: China Machine Press) p90 (in Chinese) [金维芳 1997 电介质物理学 (北京: 机械工业出版社) 第90页]
[9] Kremer F, Schönhals A 2003 Broadband Dielectric Spectroscopy (Berlin: Springer) p385
[10] Kao K C 2004 Dielectric Phenomena in Solids (San Diego: Elsevier Academic Press) p41
[11] Lowell J 1990 J. Phys. D: Appl. Phys. 23 205
[12] Min D M, Li S T, Ohki Y 2015 IEEE 11th International Conference on the Properties and Applications of Dielectric Materials Sydney, Australia, July 19-22 2015 p368
[13] Xu J, Li J 1999 Acta Phys. Sin. 48 1930 (in Chinese) [徐敬, 李杰 1999 48 1930]
[14] Ning C F, He C Q, Zhang M, Hu C P, Wang B, Wang S J 2001 Acta Polym. Sin. 1 299 (in Chinese) [宁超峰, 何春清, 张明, 胡春圃, 王波, 王少阶 2001 高分子学报 1 299]
[15] Wei L, Zhou L L, Lu G H, Zhang W, Zhang W Z, Zhang S, Feng Y H, Zhou H W, Zhang J L, Huang Y N 2012 Acta Phys. Sin. 61 017701 (in Chinese) [卫来, 周兰兰, 鹿桂花, 张文, 张武智, 张尚, 冯永红, 周恒为, 张晋鲁, 黄以能 2012 61 017701]
[16] Badawia A, Al-Hosiny N 2015 Chin. Phys. B 24 105101
[17] Li S T, Yin G L, Bai S N, Li J Y 2011 IEEE Trans. Dielectr. Electr. Insul. 18 1535
[18] Min D M, Li S T, Hirai N, Ohki Y 2015 Proceedings of the 46th Symposium on Electrical and Electronic Insulating Materials and Applications in Systems Kyushu, Japan, September 4-6, 2015 p39
[19] He M J, Chen W X, Dong X X 1990 Polymer Physics (Shanghai: Fudan University Press) p224 (in Chinese) [何曼君, 陈维孝, 董西侠 1990 高分子物理 (上海: 复旦大学出版社) 第224]
[20] Alvarez F, Alegría A, Colmenero J 1991 Phys. Rev. B 44 7306
[21] Angell C A 1997 Polymer 38 6261
[22] Dudowicz J, Freed K F, Douglas J F 2005 J. Phys. Chem. B 109 21285
[23] Schönhals A, Kremer F, Hofmann A, Fischer E W, Schlosser E 1993 Phys. Rev. Lett. 70 3459
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