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 crosslinked 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 directcurrent 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.