Water-Tree Resistant Characteristics of Crosslinker-Modified-SiO2/XLPE Nanocomposites.

Yong-Qi Zhang,Wei-Feng Sun,Ping-Lan Yu,Xuan Wang

doi:10.3390/ma14061398

Yong-Qi Zhang, Wei-Feng Sun + Show 2 more

Open Access

https://doi.org/10.3390/ma14061398

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Abstract

Trimethylolpropane triacrylate (TMPTA) as a photoactive crosslinker is grafted onto hydrophobic nanosilica surface through click chemical reactions of mercapto double bonds to prepare the functionalized nanoparticles (TMPTA-s-SiO2), which are used to develop TMPTA-s-SiO2/XLPE nanocomposites with improvements in mechanical strength and electrical resistance. The expedited aging experiments of water-tree growth are performed with a water-knife electrode and analyzed in consistence with the mechanical performances evaluated by means of dynamic thermo-mechanical analysis (DMA) and tensile stress–strain characteristics. Due to the dense cross-linking network of polyethylene molecular chains formed on the TMPTA-modified surfaces of SiO2 nanofillers, TMPTA-s-SiO2 nanofillers are chemically introduced into XLPE matrix to acquire higher crosslinking degree and connection strength in the amorphous regions between polyethylene lamellae, accounting for the higher water-tree resistance and ameliorated mechanical performances, compared with pure XLPE and neat-SiO2/XLPE nanocomposite. Hydrophilic TMPTA molecules grafted on the nano-SiO2 surface can inhibit the condensation of water molecules into water micro-beads at insulation defects, thus attenuating the damage of water micro-beads to polyethylene configurations under alternating electric fields and thus restricting water-tree growth in amorphous regions. The intensified interfaces between TMPTA-s-SiO2 nanofillers and XLPE matrix limit the segment motions of polyethylene molecular chains and resist the diffusion of water molecules in XLPE amorphous regions, which further contributes to the excellent water-tree resistance of TMPTA-s-SiO2/XLPE nanocomposites.

Highlights

As the most important constituent of a power cable, the electrical insulation layer determines the transmission capacity and operating conditions of power system [1]
Auxiliary crosslinker Trimethylolpropane triacrylate (TMPTA) has successfully been grafted onto nano-SiO2 surfaces by click chemical reactions of mercapto double-bonds, based on which UV-initiated XLPE nanocomposites are developed to ameliorate water-tree resistant characteristics for submarine cable fabrications
By means of water-knife electrode method, the accelerated water-tree aging experiments are carried out to investigate the modification mechanism of nano-SiO2 functionalized with auxiliary crosslinker to inhibit water-tree growth in XLPE matrix

Summary

Introduction

As the most important constituent of a power cable, the electrical insulation layer determines the transmission capacity and operating conditions of power system [1]. The formation and growth of water-trees rely on external factors, such as the strength and frequency of the applied electric field and operation time, and on intrinsic features such as crystal morphology and additive content in insulating materials [9,10,11,12] It is of great significance for the safe operation of power cable to improve the water-tree resistance of XLPE insulation materials. We combine polar-compound modification with nanodielectric technology, to avoid thermal migrations of small crosslinker molecules out of polyethylene matrix, and to chemically introduce SiO2 nanofillers into XLPE crosslinked network This will effectively enhance molecular-chain interactions in the amorphous regions connecting crystal lamellae so as to achieve amelioration in mechanical properties and water-tree-resistant characteristics.

Characterization and Testing Methodology

Material Characterization

Conclusions