Color reduction in polyethylene modified by radical initiation
Polyethylene modified by using radical initiators such as oxygen and peroxides sometimes has a yellow color which may be reduced or eliminated by incorporating additives such as polyethylene glycol, and/or neutralizing species such as alkali metal stearates, particularly calcium stearate, and zinc oxide.
1. Polyethylene having reduced color made by a process comprising polymerizing ethylene monomer in the presence of at least one free radical initiator as a polymerization mixture; and incorporating into the polymerization mixture an amount effective to reduce a yellow index of a polyethylene product an additive selected from the group consisting of alcohols, glycols, and water steam, and a neutralizing species selected from the group consisting of alkali metal stearates, alkali earth metal stearates, zinc stearate, calcium oxide and zinc oxide, and combinations thereof.
2. The polyethylene of claim 1 where the free radical initiator is selected from the group consisting of oxygen and peroxides.
3. The polyethylene of claim 1 where the proportion of additive is between about 5 and about 1000 ppm when the additive is alcohol, glycol, polyol or water steam, between about 300 to about 2000 ppm when the additive is a stearate, and between about 300 to about 4000 ppm when the additive is zinc oxide or calcium oxide, based on the polymerization mixture.
4. The polyethylene of claim 1 where the polyethylene product has reduced yellow index as compared with an identical polyethylene product absent the additive.
5. The polyethylene of claim 1 where the alkali earth metal stearate is calcium stearate.
6. An article of manufacture comprising a polyethylene of claim 1 .
7. The article of manufacture of claim 6 wherein the article comprises a film, a fiber, or is a blow molded or injection molded article.
8. An article wrapped in a film of claim 7 .
9. Polyethylene having reduced yellow index made by a process comprising polymerizing ethylene monomer in the presence of at least one free radical initiator as a polymerization mixture; and incorporating into the polymerization mixture an additive selected from the group consisting of alcohols, glycols, and water steam, in a proportion between about 5 and about 1000 ppm, a stearate selected from the group consisting of alkali metal stearates, alkali earth metal stearates, zinc stearate, in a proportion between about 300 to about 2000 ppm, and zinc oxide or calcium oxide in a proportion between about 300 to about 4000 ppm; all based on the polymerization mixture; where the polyethylene has reduced yellow index as compared with an identical polyethylene absent the additive.
10. The polyethylene of claim 9 where the free radical initiator is selected from the group consisting of oxygen and peroxides.
11. An article of manufacture comprising a polyethylene of claim 9 .
12. The article of manufacture of claim 11 wherein the article comprises a film, a fiber, or is a blow molded or injection molded article.