Click chemistry‐type crosslinking of a low‐conductivity polyethylene copolymer ternary blend for power cable insulation

Abstract

High‐voltage direct‐current power cables are vital for the efficient transport of electricity derived from renewable sources of energy. The most widely used material for high‐voltage power cable insulation – low‐density polyethylene (LDPE) – is usually crosslinked with peroxides, a process that releases unwanted by‐products. Hence, by‐product‐free crosslinking concepts that mitigate the associated increase in electrical conductivity are in high demand. Click chemistry‐type crosslinking of polyethylene copolymer mixtures that contain glycidyl methacrylate and acrylic acid co‐monomers is a promising alternative, provided that the curing reaction can be controlled. Here, we demonstrate that the rate of the curing reaction can be adjusted by tuning the number of epoxy and carboxyl groups. Both dilution of copolymer mixtures with neat LDPE and the selection of copolymers with a lower co‐monomer content have an equivalent effect on the curing speed. Ternary blends that contain 50 wt% of neat LDPE feature an extended extrusion window of up to 170 °C. Instead, at 200 °C rapid curing is possible, leading to thermosets with a low direct‐current electrical conductivity of about 10−16 S cm−1 at an electric field of 20 kV mm−1 and 70 °C. The conductivity of the blends explored here is comparable to or even lower than values measured for both ultraclean LDPE and a peroxide‐cured commercial crosslinked polyethylene grade. Hence, click chemistry curing represents a promising alternative to radical crosslinking with peroxides. © 2019 Society of Chemical Industry

Electrical Characterization of a New Crosslinked Copolymer Blend for DC Cable Insulation

“…For the calculations, the attempt to escape frequency v was assumed to be equal to 10 11 s -1 [38,44]. The two copolymers that we use to prepare the here studied binary blend are LDPE type materials that comprise a low amount of acrylic acid or glycidyl methacrylate comonomers [32,33]. Since the attempt to escape frequency is linked to the nanostructure of an insulation material [49] we here use the same value for the copolymer blend and LDPE to interpret our data.…”

“…Recently, other types of copolymer blends with similar electromechanical properties to XLPE have gained interest among materials scientists [19,22,[29][30][31][32][33]. For example, [19,22] investigated polyethylene-based copolymers in terms of structural, morphological, mechanical and electrical properties.…”

“…For example, [19,22] investigated polyethylene-based copolymers in terms of structural, morphological, mechanical and electrical properties. In previous studies [29][30][31][32][33], we have introduced a byproduct-free crosslinking method based on click chemistry-type reactions for the development of polyethylene-based insulations. In these novel materials, there is no trace of detrimental by-products, and therefore the degassing process, which is a long and costly part of high-voltage cable manufacturing, is omitted.…”

“…Preliminary investigations presented in [32] indicated promisingly low DC conductivities (measured with broadband dielectric spectroscopy) of the obtained materials in comparison with commonly used high voltage insulation materials (including XLPE). A proof-of-concept study included DC conductivity measurements at specific/desired operational conditions [33]. However, additional advanced electrical characterization needs to be done to shed light on the underlying charge transport mechanisms involved.…”

“…Here, low-density polyethylene (LDPE) and its crosslinked version XLPE were selected as reference materials. In the previous studies [32,33], electrical characterizations were limited to broadband dielectric spectroscopy at a very low electric field stress of 10 V/mm and high-voltage DC conductivity measurements at a specific condition (70 • C, 20 and 30 kV/mm). Therefore, it is important to evaluate the new material at different high-voltage conditions, which may permit to identify the underlying charge transport mechanisms.…”