XLPE

XLPE stands for cross-linked polyethylene, a thermally improved form of polyethylene in which polymer chains are covalently bonded to form a three-dimensional network. This crosslinking enhances heat resistance, mechanical strength, chemical resistance, and electrical insulation, making XLPE a primary insulation material in many medium- and high-voltage cables and used as a jacket material in some cable designs.

Crosslinking can be achieved by several processes: peroxide-initiated thermal crosslinking, silane-grafting followed by moisture cure, and irradiation with electrons or gamma rays. Peroxide crosslinking occurs during or after extrusion at elevated temperature and produces a network with high heat resistance. Silane crosslinking uses vinylsilane groups grafted onto the polyethylene and then cured by moisture, yielding XLPE that can be extruded and cured later. Radiation crosslinking exposes the extruded material to ionizing radiation, enabling rapid production without added solvents or additives.

Key properties include high thermal endurance (continuous rating typically around 90°C for many cable insulations, with some formulations rated up to 105°C or higher), low dielectric loss, resistance to aged oxidation, and good mechanical durability. XLPE also exhibits excellent resistance to moisture ingress and to many chemicals compared with unmodified polyethylene.

Limitations include non-reversible crosslinks that prevent remelting, which complicates recycling; manufacturing requires specialized crosslinking equipment; flame retardant performance is achieved with additives, influencing processing and properties. XLPE insulation is commonly combined with a polymer jacket to form cables that comply with international standards, providing fire performance and dimension stability.

XLPE has become a standard material for many low- and medium-voltage cables, including submarine and indoor installations, valued for high-temperature operation and long-term durability.