Investigating the impact of hardness on dielectric breakdown characteristics of polyurethane

Samad, Abdul and Siew, Wah Hoon and Given, Martin and Liggat, John and Timoshkin, Igor (2024) Investigating the impact of hardness on dielectric breakdown characteristics of polyurethane. ACS Omega, 9 (23). pp. 24538-24545. ISSN 2470-1343 (

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Polymeric materials play a vital role in high voltage insulation, but their insulating properties can deteriorate over time, leading to insulation failures. The presence of voids resulting from manufacturing defects or external stresses can create a highly divergent field, further contributing to this issue. However, certain polymers, such as polyurethane (PU), possess self-healing properties that enable them to repair these voids and restore a uniform electric field distribution, thereby ensuring the reliability of the insulation. Surprisingly, the potential of PU as an insulating material in high voltage applications remains unexplored. However, the self-healing capability of PU decreases with the increased hardness of the material. Therefore, in this study, the dielectric breakdown properties of PU with different levels of hardness, rated on the Shore scale as 400 (soft), 700 (medium), and 900 (hard), were investigated. AC and DC dielectric breakdown characteristics of these PU variants and dielectric spectra were examined. Additionally, the study explores the relationship between the dielectric properties and the hardness of the material. Our findings revealed that the dielectric breakdown strength of PU increases as the material's hardness is increased under both AC and DC electric stress. However, this may come at the cost of reduced self-healing capabilities of PU. Therefore, there is a need to balance the hardness of the material with its ability to recover from breakdown events. The findings from this study can be useful for researchers and engineers as they offer valuable insights into the dielectric properties of PU at various hardness levels.