The article discusses two types of Hi-fax to the wire and cable industry. The 1600 type is recommended for use in all applications not requiring the ultimate in stress-crack resistance. This type has moderate stress-crack resistance, somewhat better than the stress-crack resistance of 1-2 melt index low molecular weight polyethylene which has found wide acceptance in this market. The heat-shock resistance of 1600 Hi-fax at normal operating temperatures is at least comparable to the heat-shock resistance of 1-2 melt index low density polyethylene. Extended exposure to high temperatures is not recommended for either low density polyethylene or Hi-fax because of the susceptibility to oxidation. However, even at 90C., the heat-shock resistance of 1600 type Hi-fax is very good. Applications such as cable sheaths, where the ultimate in stress-crack resistance is required, require use of 1800 type Hi-fax. Although this is a higher molecular weight resin than the 1600 type, it has similar physical and electrical properties, but has a substantially higher level of stress-crack and heat-shock resistance. The higher molecular weight resin will withstand more than 1,000 hours' exposure without failure in the Bell Laboratories stress-cracking test. Therefore, in stress-crack resistance, it is equivalent to the low melt index, low density polyethylene now used for sheaths.
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