Epoxy composites with flame-retardant fillers are key electrical insulation materials for dry-type high-voltage (HV) transformers, but the ionic structure nature of the flame-retardant fillers can lead to the deterioration of the insulation performance, limiting the reliability of HV power systems. This study systematically examines how flame-retardant filler introduction and interface structure evolution impact charge transport within composites, aiming to refine the design principles of flame-retardant electrical insulation materials. Composites with uniformly dispersed fillers and ideal interfacial bonding with the matrix exhibit improved resistivity (1.41 × 10 16 Ω cm), attributed to the dense cross-linked network that limits impurity ion movement. More importantly, the behavior of space charge accumulation and dissipation within the composites indicates that the interfacial structure affects the internal energy level distribution, thereby influencing charge carrier transport characteristics. By optimizing the interfacial structure, the suppression of electrode charge injection and reduction of electric field distortion (from 15.1 % to 8.5 %) enhance the electrical insulation reliability of epoxy composites. These findings deepen the understanding of structure-property relationships in epoxy composites, offering critical insights for designing advanced flame-retardant HV electrical insulation materials.
Changfa Xiao,Qingshan Yang,Kefu Shao,Yongjiang Li,Songhan Wan,Xianru He
The vulcanization reaction of ethylene vinyl acetate copolymer (EVM) rubber is fast, resulting in poor processing safety. EVM is often filled with flame-retardant fillers as insulating or sheathing material for wires and cables. Herein, the effects of flame-retardant magnesium hydroxide (Mg(OH) 2 ), aluminum hydroxide (Al(OH) 3 ) and of the traditional reinforcing fillers carbon black (CB) and silicon dioxide (SiO 2 ) on the vulcanization kinetics of EVM were investigated. The vulcanization characteristics showed that the scorch time ( T 10 ) of the unfilled EVM (KB), SiO 2 /EVM, Mg(OH) 2 /EVM, and Al(OH) 3 /EVM composites was about 1.75 min. T 10 of the CB/EVM composite was 2.22 min. Compared with KB, the activation energy ( E
a
) increased by about 15 kJ/mol for CB/EVM composites and by about 5 kJ/mol for SiO 2 /EVM, Mg(OH) 2 /EVM and Al(OH) 3 /EVM composites. The results indicate that CB delays the vulcanization time of EVM rubber, slows down the rate of vulcanization reaction and improves the safety of vulcanization. The addition of SiO 2 , Mg(OH) 2 and Al(OH) 3 has little effect on the vulcanization reaction. The mechanical properties show that CB/EVM is more uniformly vulcanized and has the best mechanical properties with a tensile strength of 17.61 MPa and elongation at break of 404.58 %. Mg(OH) 2 /EVM and Al(OH) 3 /EVM samples have prominent vulcanization non-uniformity resulting in poor mechanical properties.
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