Stabilized polyethylene material
Stabilized polyethylene materials which offer an advantageously balanced combination of thermal, mechanical and processing properties, and which maintain their physical properties in chlorinated water environments are disclosed. The materials include an antioxidant system with components to provide extraction resistance in hot water environments and additionally provides oxidation resistance to both chlorine in the water interior of the pipe and oxygen in contact with the pipe's exterior.
1. A process for making a pipe consisting essentially the steps of:
selecting an ethylene alpha-olefin interpolymer composition, wherein said ethylene alpha-olefin interpolymer composition has a density in the range of 0.925 to 0.965 g/cc, a melt index (I 2 ) in the range of 0.05 to 5 g/10 minutes; and
selecting an antioxidant system, wherein said antioxidant system consist essentially of;
from 500 to 5000 ppm of 3,3′,3″,5,5′,5″-hexa-tert-butyl-α, α′, α″-(mesitylene-2,4,6-triyl)tri-p-cresol;
from at least 300 to 5000 ppm of Pentaerythritol Tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), Octadecyl-3-(3,5-di-tert.butyl-4-hydroxyphenyl)-propionate, or combinations thereof;
from 500 to 5000 ppm of Tris(2,4-ditert-butylphenyl) phosphate;
optionally one or more metal deactivators;
forming said alpha-olefin interpolymer composition and said antioxidant system into a pipe;
wherein said pipe has an F time in Jana Laboratories Procedure APTF-2 of at least 1000 hours, under the following conditions: pH 6.8 (±0.1); Chlorine 4.1 mg/L (±0.1); Nominal ORP 830mV; fluid temperature 110° C. (±1); air temperature 110° C. (±1); pressure 70 psig (±1); flow rate 0.1 US gallons/min (±10 percent).
2. The process of claim 1 , wherein the ethylene alpha-olefin interpolymer composition is multimodal.
3. The process of claim 1 , wherein the ethylene alpha-olefin interpolymer composition has a density in the range of 0.940 to 0.965 g/cc.
4. The process of claim 1 , wherein said pipe has an F time in the range of greater than 1200 hours.