CROSS-LINKABLE POLYETHYLENE (XLPE)
What is Cross-linkable polyethylene?
Crosslinked polyethylene (XLPE, XPE, PEX) is a chemically processed high-density polyethylene that can be interlinked with moisture, radiation, catalysts or chemicals. The crosslinking transforms polyolefin resins into insoluble and infusible polymers with dramatically increased impact strength and heat distortion but decreased melt index and elongation at release. Crosslinking also significantly increases crack tolerance, abrasion and environmental tension. It’s density and tensile strength are not or is just partially influenced by crosslinking.
Types of Cross-Linkable Polyethylene
Silane cross-linked polyethylene – Vinylsilane is grafted into a double bond with polyethylene through a free-radical reaction. Silane grafting is usually done in the molten state in a limited volume of peroxide by reactive extrusion. Extruded articles are then cross-linked by exposure to steam or hot water.
Irradiation cross-linked polyethylene – Formed polyethylene articles are subjected to extreme radiation such as gamma rays or electrons that create free radicals which, in turn, cause crosslinking. The procedure is usually conducted in an inert environment to avoid oxidative degradation. Radiation crosslinking is less commonly used due to high capital and maintenance costs than peroxide or silane crosslinking.
Peroxide cross-linked polyethylene – Polyethylene granulates and peroxides (di-dicumyl peroxide or di-tert-butyl peroxide) are combined at low temperatures in the extruder and then crosslinked at high temperatures. Peroxide is decomposed by the formation of peroxide radicals abstracting hydrogen atoms from the polymer backbone—the generated radicals on the polymer backbone combine and form crosslinks.
Applications of Cross-Linkable Polyethylene
XLPE is manufactured on a much smaller scale than normal high-density polyethylene (HDPE). It is also an ideal alternative for applications needing increased chemical and/or resistance to abrasion at an affordable cost. Important uses include wire and cable insulation, pipe and fittings, face plates, and injection moulded parts. We recommend using our quality crimping tools for cutting and crimping cross-linked polyethylene.
