Recyclable Polyethylene Insulation via Reactive Compounding with a Maleic Anhydride-Grafted Polypropylene

Abstract

The most common type of extruded power cable insulation is based on cross-linked polyethylene (XLPE), which cannot be recycled as a thermoplastic material. Hence, thermoplastic insulation materials currently receive considerable attention because they would allow recycling through re-melting. In particular blends of polyethylene (PE) and polypropylene (PP) would be a compelling alternative to XLPE, provided that the poor compatibility of the two polymers can be overcome. Here, we establish an alternative approach that exploits the in situ formation of a PE–PP-type copolymer through reactive compounding. Ternary blends of an ethylene-glycidyl methacrylate copolymer, a maleic anhydride-grafted polypropylene, and up to 70 wt % low-density polyethylene (LDPE) are compounded at 170 °C. Covalent bonds form through reaction between epoxy and carboxyl groups, leading to a PE–PP-type copolymer that shows good compatibility with LDPE. The in situ generated PE–PP copolymer arrests creep above the melting temperature of LDPE, mediated by a continuous network that is held together by PP crystallites. Recyclability is confirmed by reprocessing at 170 °C. Furthermore, the here investigated formulations feature a low direct-current electrical conductivity of ∼4 × 10–14 S m–1 at 70 °C and 30 kV mm–1, on a par with values measured for LDPE and XLPE. Evidently, in situ formation of a PE–PP-type copolymer through reactive compounding is a promising approach that may enable the design of thermoplastic insulation materials for power cables.

High‐temperature creep resistant ternary blends based on polyethylene and polypropylene for thermoplastic power cable insulation

“…For neat LDPE, we obtained σ DC~3 6 Â 10 À15 S m À1 , in agreement with previous reports. 21,46 SEBS:(PP: LDPE) 25:75 ternary blends instead displayed significantly lower values of σ DC~1 5 Â 10 À15 and 3.4 Â 10 À15 S m À1 in case of a SEBS content of 10 and 5 wt%, respectively (Table 1). We attribute the excellent insulating properties of the ternary blends to the low σ DC~1 .0 Â 10 À15 S m À1 of neat PP.…”

“…[17][18][19][20] LDPE-based blends that incorporate a small amount of PP but maintain the cleanliness and mechanical flexibility of LDPE have received little attention. 21 Unfortunately, PP and LDPE are immiscible. 22,23 The thermomechanical properties of PP:LDPE binary blends can be enhanced by adding a sufficiently large amount of PP, which however unduly increases the stiffness of the material at low temperatures.…”

“…22,23 The thermomechanical properties of PP:LDPE binary blends can be enhanced by adding a sufficiently large amount of PP, which however unduly increases the stiffness of the material at low temperatures. Instead, one can incorporate PP into LDPE in the form of a PP copolymer, 15,16,24 use reactive compounding, 21 or use additives to modify the PP:LDPE interface. 25 The latter strategy, to our knowledge, has not been reported within the context of power cable insulation.…”

“…LDPE‐based blends that incorporate a small amount of PP but maintain the cleanliness and mechanical flexibility of LDPE have received little attention 21 . Unfortunately, PP and LDPE are immiscible 22,23 .…”

Enhanced Morphology-Dependent Tensile Property and Breakdown Strength of Impact Polypropylene Copolymer for Cable Insulation

“…Christian Müller et al synthesized an ethylene-propylene copolymer, which showed good compatibility with low-density polyethylene (LDPE). They also found that the blend of polyethylene (PE)–PP copolymers and LDPE exhibited excellent melt creep resistance and dielectric properties at operating temperatures [ 9 , 10 ]. It can be seen that a multisystem with good compatibility can synergistically improve the mechanical and electrical properties of the polymer, but the high cost caused by the complex production process is also an issue that has to be considered.…”