Crosslinked polyethylene thermal properties

Polyethylene is known as one of the typical polymers which crosslink under the influence of ionizing radiation. The radiation-induced crosslinking (the formation of C-C covalent bonds between polymer chains) of polyethylene has long attracted the interest of a large number of research workers, because this polymer has the most simple chemical structure for the fundamental study of radiation effects on polymers, and also because the irradiation with ionizing radiation is a practically important means of modifying the mechanical and thermal properties of polyethylene. 

Abt N.A., and W. Schneider. 2003. Influence of irradiation on the properties of UHMWPE. In Highly crosslinked and thermally treated ultra-high molecular weight polyethylene for joint replacements. S.M. Kurtz, R. Gsell, and J. Martell, Eds. West Conshohoken, PA American Society for Testing and Materials. 

Nedjar [32] has reported on the measurement of volume resistivity of crosslinked polyethylene (XLPE) grades used in high voltage cables and the effect of thermal aging on the electrical properties of the cable. 

Carbon black can fnnction as a UV stabilizer, thermal antioxidant, extender in crosslinked polyethylene (XLPE) cable compounds, antistat in vinyl records, modifier of polymerization rate in nnsaturated polyesters, conductive filler, and colorant. Although commonly used in rubbers and thermoplastics, carbon black does not improve the properties of thermosetting resins significantly. However, it is often used as a pigment and for obtaining electrical conductivity. 

The product in both cases was a white powder which possessed similar physical properties to polytetraf1uoroethylene. The powder did not have a sharp melting point and was thermally stable to 34S°C in air, where it decomposed to fluorocarbon materials slowly if heated for long periods of time at 350-400°C. With conventional polyethylene starting material, a more crosslinked fluorocarbon polymer is obtained of higher molecular weight and slightly inferior thermal properties. The parent polyethylene melted at about 70°C in air. 

Abt NA, Schneider W, Schon R, Rieker CB. Influence of electron beam irradiation dose on the properties of crosslinked UHMWPE. In Kurtz SM, GseH RA, Martell J, editors. Crosslinked and thermally treated ultra-high molecular weight polyethylene for joint replacements. West Conshohocken, Pa. ASTM International 2004. 

PVC, another widely used polymer for wire and cable insulation, crosslinks under irradiation in an inert atmosphere. When irradiated in air, scission predominates.To make cross-linking dominant, multifunctional monomers, such as trifunctional acrylates and methacrylates, must be added. Fluoropolymers, such as copol5miers of ethylene and tetrafluoroethylene (ETFE), or polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF), are widely used in wire and cable insulations. They are relatively easy to process and have excellent chemical and thermal resistance, but tend to creep, crack, and possess low mechanical stress at temperatures near their melting points. Radiation has been found to improve their mechanical properties and crack resistance. Ethylene propylene rubber (EPR) has also been used for wire and cable insulation. When blended with thermoplastic polyefins, such as low density polyethylene (LDPE), its processibility improves significantly. The typical addition of LDPE is 10%. Ethylene propylene copolymers and terpolymers with high PE content can be cross-linked by irradiation. ... 

Paraffin wax has been found to have an influence on the thermal and mechanical properties of low-density polyethylene (LDPE) [39,40]. It crosslinks to improve the mechanical properties of LDPE, short sisal fibres composites [42,43] and PVC. There is complete miscibility of the wax in LDPE at wax concentrations up to 10%, but only partial miscibility at higher wax concentrations. On blending an oxidised paraffin wax with LDPE, small wax concentrations improved the physical properties of the blends [40]. 

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