ABSTRACT High-density polyethylene (HDPE) has many applications, including in the electrical sector, due to its excellent electrical, mechanical, and thermal properties. In insulators employed in electricity networks, the material is exposed to various adverse conditions (solar radiation, humidity, temperature cycles, and pollution), which can accelerate degradation of the polymer, modifying its properties and affecting its performance in the field. The surface resistivity of HDPE hinders the transmission of electrical current on the surface, consequently avoiding tracking. However, factors such as contamination of the surface by industrial pollutants, salt, and other agents, together with high humidity, act to decrease the surface resistivity, facilitating the flow of current between different potentials and initiating the electrical tracking process, which can lead to loss of the insulation property. In order to avoid electrical tracking, it is important to prevent the adhesion of dirt on the surface of the insulator, which can be achieved by the provision of a hydrophobic surface. The aim of this work was to modify the surface of HDPE using a coating of TiO2 nanoparticles. The nanoparticles were functionalized to optimize adhesion to the polymer surface during immersion processes, obtaining hydrophobic surfaces with self-cleaning characteristics that could improve performance when applied to insulators. Four different functionalization agents were studied, with different carbon chain lengths: trimethoxypropylsilane (TMPSi), trimethoxyoctylsilane (TMOSi), trimethoxyhexadecylsilane (TM16Si), and trimethoxyoctadecylsilane (TM18Si). The modification of the nanoparticle surface was confirmed by analysis using Fourier transform infrared (FTIR) spectroscopy. The HDPE sample surfaces showed good adhesion of the functionalized nanoparticles, with enhanced hydrophobicity.

Abstract Insulating paper holds significant importance in the insulation system of power transformers, and thus, its degradation is the subject of many studies. A successful evaluation of the degradation rate of such paper contributes to reducing downtime and avoiding equipment failure. In this work, samples of thermally upgraded paper were thermally aged in insulating natural ester (INE) and insulating mineral oil (IMO) and were evaluated by degree of polymerization (DP) and FTIR-ATR. It was possible to identify characteristic bands of dicyandiamide, an inhibitory compound of the thermal degradation of the paper, and to establish a correlation between the decrease in DP and the consumption of dicyandiamide during aging, which was observed to develop in three distinct steps for both IMO and INE.