Polyolefins polyethylene wire cable

Though there are metals other than copper (such as iron, manganese and cobalt) that can accelerate thermal oxidation of polyolefins and related polymers such as EPDM, in practice, however, the inhibition of copper-catalyzed degradation of polyolefins is of paramount importance because of the steadily increasing use of polyolefin insulation over copper conductors. Among polyolefins, polyethylene is still the most common primary insulation material for wire and cable. In the United States, high-density polyethylene and ethylenepropylene copolymers are used in substantial amounts for communications wire insulation. 

Cross-linkable polymers used for wire and cable insulations are polyolefins, certain fluoropolymers, and elastomers. Among these, radiation cross-linked polyethylene is the most widely used. The radiation cross-linking process of PE has also been the most widely studied. ... 

Irradiation of polyolefins, particularly the family of polyethylenes, represents an important segment of the radiation processing. Polyolefins can be irradiated in many forms, such as pellets and powders, films, extruded and molded parts or as wire and cable insulation. 

The most common polymers used in FR wire and cable applications are PVC, polyolefins, fluoropolymers, and silicone polymers. Thermoplastic polyurethanes (TPUs) and other specialty polymers such as chlorosulfonated polyethylene also serve niche applications in wire and cable. The approaches to achieve flame retardancy in each of these polymer systems along with issues unique to wire and cable application are discussed in the following sections. 

After PVC, polyolefin copolymers, predominantly polyethylene copolymers, are the next most widely used material for FR applications in wire and cable. Polyethylenes have very good dielectric strength, volume resistivity, mechanical strength, low temperature flexibility, and water resistance. In contrast to PVC, polyolefins are not inherently FR and thus are more highly formulated, requiring the addition of FRs to meet market requirements for flame retardancy. For this reason, and because of the steady global trend toward halogen-free materials for wire and cable applications, more space will be devoted to this section on FR polyolefins compared with the above discussion of PVC. 

Cross-linking can also be achieved by compounding a polymer with a peroxide such as dicumyl peroxide or di-/-butyl praoxide, followed by heating. This technique, although economically disadvantageous compared to sulfur vulcanization, is particularly useful for saturated polymers that cannot be easily cross-hnked, particularly polyethylene and other polyolefins. Similar results can be obtained through radiation cross-linking, and this method is employed commercially in the production of electrical wires and cable insulation made of polyolefins and poly(vinyl chloride). 

Oxidative induction time (OIT) provides an index useful in comparing the relative resistance to oxidation of a variety of hydrocarbon materials. The OIT procedure was first developed in 1975 by Gilroy and coworkers at Bell Laboratory as a test procedure to screen polyethylene insulation used in telephone wire and cable for its oxidation resistance. The method first became available as a Western Electric Specification and later as ASTM Test Method for Copper-Induced Oxidative Induction Time of Polyolefins. Polyolefin manufacturers quickly embraced the procedure and began to apply it to other applications including raw resins, finished pipes, wire and cable insulation, and, most recently, geosynthetic waste pit liners (ASTM D3895 2009). 

There is a growing demand for Tow smoke zero halogen compositions in wire and cable. In 2002, such grades amounted to 15% of all the polyethylene cable compounds used in Western Europe. Antioxidants and metal deactivators are used to protect the insulation against copper compoimds that can otherwise promote failure in polyolefins. The additives need to withstand prolonged heat and to resist migration and decomposition. 

Polyolefin blends are of critical importance to the success of the material. Ethylene propylene diene rubber (EPDM) immiscibly blends with PP as an impact modifier. It is the most common and most commercially utilised blend of polyolefins. High-density polyethylene (HOPE) can be added to this blend to achieve maximum toughness [11-13]. Applications include wire and cable insulation, automotive... 

The polyolefin block copolymers are lower in cost. Their suggested applications (74) include wire and cable insulation, replacements for PVC and styrenic block copolymers, and blends with polypropylene, either to improve impact resistance or as the soft phase in a hard polymer/elastomer combination. Processing conditions are similar to those for polyethylene, and thermal stability is excellent. 

In polyolefins, it is used mainly in LDPE wire and cable insulation. Other uses reported or claimed include EVA wire and cable and foam carpet-backing EMA wire and cable EPR and EPDM wire and cable, electrical insulation, roofing, and automotive parts— white-wall tires, hoses, seals, and weather stripping XLPE wire and cable chlorosulfonated polyethylene and HDPE and polybutene. There is considerable interest in its use in PP cabinets (less smoke than polystyrene). 

Beside the compounds in which the characteristic constituents are polyolefins, other products also may be employed for insulation and jackets. These include crosslinked compounds and constituted from chloro-sulfonated polyethylene (CP insulation and jackets for wires and cables used for deep wall submersible pumps subjected to 60, 90, and 105°C) chlorinated polyethylene (CPE Insulation and jackets for wires subjected to 90°C) ethylene-propylene-diene monomer (EDPM)... 

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