Color reduction 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. A method for producing polyethylene having reduced color 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 method of claim 1 where the free radical initiator is selected from the group consisting of oxygen and peroxides.
3. The method 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 method of claim 1 where the polyethylene product has reduced color as compared with an identical polyethylene product absent the additive.
5. The method of claim 1 where the alkali earth metal stearate is calcium stearate.
6. The method of claim 1 further comprising blowing a film of the polyethylene.
7. A method for producing polyethylene having reduced color 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 product has reduced yellow index as compared with an identical polyethylene product absent the additive.
8. The method of claim 7 where the free radical initiator is selected from the group consisting of oxygen and peroxides.