and 2% peroxide is at first mixed at low temperatures in an extruder and then crosslinked at high temperatures (between 200 °C and 250 °C). The peroxide decomposes to peroxide radicals (RO•), which abstract (remove) hydrogen atoms from the polymer chain, leading to radicals. When these combine, a crosslinked network is formed. The resulting polymer network is uniform, of low tension and high flexibility, whereby it is softer and tougher than (the irradiated) PE-Xc. The same process is used for LDPE as well, though the temperature may vary from 160 °C to 220 °C. Silane crosslinking (PE-Xb): In the presence of silanes (e.g. trimethoxyvinylsilane) polyethylene can initially be Si-functionalized by irradiation or by a small amount of a peroxide. Later Si-OH groups can be formed in a water bath by hydrolysis, which condense then and crosslink the PE by the formation of Si-O-Si bridges. [16] Catalysts such as dibutyltin dilaurate may accelerate the reaction. Irradiation crosslinking (PE-Xc): The crosslinking of polyethylene is also possible by a downstream radiation source (usually an electron accelerator, occasionally an isotopic radiator). PE products are crosslinked below the crystalline melting point by splitting off hydrogen atoms. β-radiation possesses a penetration depth of 10 mm, ɣ-radiation 100 mm. Thereby the interior or specific areas can be excluded from the crosslinking. However, due to high capital and operating costs radiation crosslinking plays only a minor role compared with the peroxide crosslinking. In contrast to peroxide crosslinking, the process is carried out in the solid state. Thereby, the cross-linking takes place primarily in the amorphous regions, while the crystallinity remains largely intact. Azo crosslinking (PE-Xd): In the so-called Lubonyl process polyethylene is crosslinked preadded azo compounds after extrusion in a hot salt bath. Degree of crosslinking A low degree of crosslinking leads initially only to a multiplication of the molecular weight. The individual macromolecules are not linked and no covalent network is formed yet. Polyethylene that consists of those large molecules behaves similar to polyethylene of ultra high molecular weight (PE-UHMW), i.e. like a thermoplastic elastomer. Upon further crosslinking (crosslinking degree about 80%), the individual macromolecules are eventually connected to a network. This crosslinked polyethylene (PE-X) is chemically seen a thermoset, it shows above the melting point rubber-elastic behavior and cannot be processed in the melt anymore. The degree of crosslinking (and hence the extent of the change) is different in intensity depending on the process. According to