Anhydride-cured bisphenol-A epoxy resin is widely used in the support, insulation and sealing key components of electrical and electronic equipment due to their excellent comprehensive performance. However, overheating and breakdown faults of epoxy resin-based insulation occur frequently under conditions of large current carrying and multiple voltage waveforms, which seriously threaten the safe and stable operation of the system. The curing regime, including mixture ratio and combination of curing time and temperature, is an important factor to determine the microstructure of epoxy resin, and also directly affects its macro performances. In this paper, the evolution of curing kinetic models of anhydride-cured epoxy resin was introduced to determine the primary curing regime. The influences of curing regime on the insulation performance were reviewed considering various mixture ratios and combinations of curing time and temperature. The curing regime-dependent microstructure was discussed and attributed to the mechanisms of insulation performance.

/pdf/curing-regime-modulating-insulation-performance-of-anhydride-go2jy9eo.pdf

Curing Regime-Modulating Insulation Performance of Anhydride-Cured Epoxy Resin: A Review

This paper offers a short overview of epoxy resins, encompassing their diverse characteristics, variants, chemical modifications, curing processes, and intriguing electrical properties. Epoxies, valued for their multifunctional attributes, serve as fundamental materials across industries. In the realm of dielectric strength, epoxy resins play a crucial role in electrical insulation. This paper discusses the mechanisms governing dielectric breakdown, strategies to enhance dielectric strength, and the impact of various fillers and additives on insulation performance. Through an exploration of recent research and advancements, this paper delves into the spectrum of epoxy properties, the array of subspecies and variants, their chemical adaptability, and the intricacies of curing. The examination of electrical resistance and conductivity, with a focus on their frequency-dependent behavior, forms a pivotal aspect of the discussion. By shedding light on these dimensions, this review provides a concise yet holistic understanding of epoxies and their role in shaping modern materials science.

A Brief Overview on Epoxies in Electronics: Properties, Applications, and Modifications

Effect of phenyl side groups on the dielectric properties and dielectric behavior of polysiloxane

The exposure of polymeric insulation in nuclear power plants necessitates the study of the effect of neutron irradiation on the mechanical and dielectric properties of neat and nano-filled polymeric-based insulation materials. The exposure of the materials to ionizing radiation can influence their dielectric and insulating properties. This work presents the influence of neutron irradiation on the dielectric behavior of neat and nanoparticle-filled Epoxy-TiO2 nanocomposite. The prepared neat and nanocomposite samples were exposed to neutron radiation in the Nigeria Research Reactor I (NIRR-I). The mechanical and dielectric analyses of the samples were performed before and after irradiation. The presence of 2 wt% TiO2 nanoparticles in the epoxy matrix resulted in optimum mechanical and dielectric behavior. While the presence of the nanoparticles seems to have a significant influence on the reduction of the mechanical degradation of the composite (39.96%–12.11% after exposure to 4.5 kGy), it does not have much influence on the reduction of the dielectric loss of the composite. The variation of temperature of the sample revealed that the 2 wt% nanoparticles filled polymer displayed higher relaxation activated energy. The research suggests that the filling of the epoxy polymer with 2 wt% TiO2 nanoparticles can modify the mechanical and dielectric relaxation behavior of the polymer composites. This could enhance the resistance of the composite material to the effect of radiation-induced degradation in the polymeric insulation. 

Influence of neutron irradiation on the mechanical and dielectric properties of epoxy/ titanium oxide nanocomposite

As the driving force for the crosslinking of epoxy resin (EP) molecular segments to form a 3-D network structure, hardener can directly affect the crosslinking degree of composite materials and then affect the formation of the two-phase structure of EP/hydroxyl-terminated liquid nitrile rubber (HTBN) composite materials. By preparing EP/HTBN rubber composites with a different hardener stoichiometry, the effects of hardener stoichiometry on the two-phase structure and electrical properties of the system are analyzed by SEM cross Section characterization, dc resistivity, and broadband dielectric spectrum. The experimental results show that deviation of the hardener from the standard stoichiometry inhibits the crosslinking behavior, which in turn promotes the precipitation of the rubber phase. The deviation of hardener from the standard stoichiometry causes an increase in dc resistivity, an increase in interfacial polarization strength, and a decrease in epoxy <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> relaxation strength. The Vogel–Fulcher–Tammann (VFT) fitting of EP <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> relaxation peak frequency versus temperature inverse was performed to obtain the Vogel temperature by Havriliak–Negami (HN) model peak separation results, and the results show that the deviation of the hardener from the standard stoichiometry causes a decrease in the glass transition temperature, which is consistent with the relationship with the crosslinking degree. The above results may provide more effective solution designs for optimizing EP/HTBN composite insulating material curing formulations. 

Effect of Hardener Stoichiometry on the Dielectric Properties of Epoxy Resin/Liquid Nitrile Rubber Composite Materials

Utilizing liquid rubber to toughen epoxy resin is one of the most mature and promising methods. However, the dielectric relaxation characteristics of the epoxy/liquid rubber composites have not been studied systematically, while the relaxation behaviours are a critical factor for both micro and macro properties. In this paper, hydroxyl-terminated liquid nitrile rubber (HTBN) is employed to reinforce a kind of room-temperature-cured epoxy resin. The dielectric spectrum is measured and analysed. Results show that two relaxation processes are introduced in the binary composites. The α relaxation of HTBN shows a similar temperature dependence with the β relaxation of epoxy resin. The interfacial polarization leads to an increase of complex permittivity, which reaches its maximum at 70 °C. In addition, affected by interfacial polarization, the thermionic polarization is inhibited, and the samples with filler ratios of 15% and 25% show lower DC-conductivity below 150 °C. In addition, the α relaxation and thermionic polarization of epoxy resin obey the Vogel‒Fulcher‒Tammann law, while the interfacial polarization and DC-conductivity satisfy with the Arrhenius law. Furthermore, the fitting results of the Vogel temperature of α relaxation, glass transition temperature, apparent activation energy of interfacial polarization and DC-conductivity all decline with HTBN content. These results can provide a reference and theoretical guidance for the assessment of dielectric properties and the improvement of the formulation of liquid-rubber-toughened epoxy resin.

https://www.mdpi.com/1420-3049/25/18/4128/pdf

Dielectric Relaxation Characteristics of Epoxy Resin Modified with Hydroxyl-Terminated Nitrile Rubber.

UHV GIS spacer is an important component in gas-insulated enclosed switchgear (GIS), and its reliability plays a vital role in the safe and stable operation of power system. Due to the differences of the electrical properties between the central conductor and basin insulation material, the interface formed by the two materials becomes the electric field strength concentration region of the spacer. During the process of operation, the ablation damage arising from the interface occurs, which is caused by partial discharge at the interface. Therefore, it is necessary to study the electric field strength concentration effect at the interface of the spacer. And the electric field strength at the interface was taken as the research object in this paper. The reason why the electric field strength at the interface of the spacer is so concentrated was analyzed by finite element simulation. The method of coating interfacial material was used to suppress the interfacial electric field concentration effect after discussion. Then the model of the spacer that coated with interfacial material was established, and the relationship between the electric field strength on both sides of the interfacial coating materials and the parameters relating to the coating material was derived. Combined with the established model and simulation, the variation of the maximum electric field strength on both sides of the interfacial layer with the dielectric parameters and the coating thickness was analyzed when there are no defects and small defects such as small burrs and bumps at the interface. The simulation results verified the validity of the established model.

Mechanism of Electric Field Control at the Interface of Central Conductor and Insulation Basin of UHV GIS Spacer

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Dielectric Relaxation Characteristics of Epoxy Resin Modified with Hydroxyl-Terminated Nitrile Rubber.

Mechanism of Electric Field Control at the Interface of Central Conductor and Insulation Basin of UHV GIS Spacer