Investigation of dielectric properties of recycled polyolefins

Abstract

This thesis investigates the dielectric behavior of post-consumer recycled polyolefins, specifically recycled high-density polyethylene and recycled polyethylene–polypropylene blends, for potential use in electrical insulation applications. The study includes detailed evaluation of their dielectric, thermal, and chemical properties under various conditions, including dry, wet, and untreated states. Blending with virgin HDPE was used as a strategy to assess whether it could improve the dielectric performance of the recycled materials. Chemical characterization revealed the presence of organic and inorganic impurities in recycled PE and PE–PP blends, which significantly affected their dielectric behavior. These impurities led to dielectric losses up to 24–28 times higher than virgin HDPE at 60 Hz and influenced breakdown strength. Recycled HDPE showed a breakdown strength of 115 kV/mm compared to 128 kV/mm for virgin HDPE, indicating that large-sized impurities negatively impact dielectric performance. Moisture absorption significantly affects the dielectric behavior of recycled polyolefins. The results show that the relaxation peak shifts to higher frequencies in wet samples, with a significant increase in dielectric loss at high frequencies and a decrease at low frequencies. At 60 Hz, the dielectric loss of wet recycled PE-PP was 71 times higher than that of untreated virgin HDPE, while wet HDPE showed only a 2-times increase, highlighting the greater moisture sensitivity of the recycled material. Blending recycled polyolefins with virgin HDPE significantly improves their dielectric performance. Even a small addition of virgin HDPE, such as 15%, reduced the dielectric loss by up to 40%, while 50% of virgin HDPE reduce the losses up to almost 70 % and improved breakdown strength. This strategy effectively moderates the negative effects of impurities and makes recycled materials more suitable for insulation applications.

Date	23 Oct 2025
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Éric David (Supervisor) & Nicole R. Demarquette (Co-supervisor)