SOME KEY PROPERTIES OF EBA BASED WIRE AND CABLE COMPOUNDS
One of the most important features of a cable is its flexibility. Flexibility requires the polymers constituting the cable to have some elastomeric character. Therefore, rubber based materials like EPDM, EPM and NBR have been used widely in wire and cable applications. However, due to its high cost EPDM and other rubbers came under pressure from elastomeric thermoplastics like ethylene butyl acrylate (EBA), ethylene vinyl acetate (EVA) and m-PE plastomers. These m-PE plastomers require a premium price due to their elaborate production technology, whereas EBA and EVA are priced relatively low due to their simple production technology. Nowadays, wire and cable formulations based on EBA or EBA / EPDM blends are very common. Lucofin® 1400HN and Lucofin® 1400MN as offered by LUCOBIT AG are typical ethylene butyl acrylates (EBA).
EPDM and other rubber based materials are vulcanized in order to increase maximum service temperature, enhance chemical as well as stress cracking resistance and improve mechanical properties during end usage. Methods of vulcanization or curing include steam, hot liquids (eutectic mixtures), microwave and hot air. Polyolefinic materials offer a very similar method of upgrading their properties: crosslinking. The resulting plastic is called cross-linked PE (XLPE). Two technologies were initially employed: crosslinking started by thermal decomposition of organic peroxides or by electron beam irradiation, both as sources of polymer radicals that combine to form a carbon-carbon bond. Peroxide crosslinking can be achieved via steam cure, nitrogen cure or pressurized liquid. Typical residence times are from 25 s for thin-walled wire, to several minutes for high-voltage power cable. All these methods involve higher heat than the melt heat to cause the peroxide in the plastic to decompose into a reactive radical and initiate the curing cycle.
Radiation crosslinking is performed by passing the wire or cable through a beam of electron radiation. Usually, the full dosage is not applied in a single pass because of the rapid temperature increase that accompanies electron beam exposure since it would damage the product. Subsequently, it was found that vinyl or acrylyl organosilanes could be grafted to PE using traces of organic peroxide, typically in an extruder, and the product then crosslinked by contact with warm water, causing hydrolysis of alkoxy groups on silicon. The resultant Si-OH groups could then be condensed to Si-O-Si linkages with catalysts such as dibutyltin dilaurate or iacetate.
As high pressure tubular reactor resins all Lucofin® grades offered by LUCOBIT AG offer excellent crosslinkability in all three crosslinking technologies as described above. Therefore, crosslinked Lucofin® based compounds are challenging vulcanized EPDM based compounds with respect to both technical properties and commercial attractiveness.