Maro Publications

Antioxidants

Notes

*11/26/2013
from 5/24/2012

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Phosphites

Stabilizers

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Notes

2. “An antioxidant is a molecule that inhibits the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When the chain reaction occurs in a cell, it can cause damage or death to the cell. Antioxidants terminate these chain reactions by removing free radical intermediates, and inhibit other oxidation reactions. They do this by being oxidized themselves, so antioxidants are often reducing agents such as thiols, ascorbic acid, or polyphenols.” (Wikipedia, Antioxidants, 5/24/2012)

1. “Polymers, e.g., polyolefins, polyvinyl halides, polyesters, polyamides, nitrile polymers, styrenic polymers and acrylate polymers, and elastomeric materials such as butadiene rubber, polyisoprene etc., are inherently unstable and susceptible to thermal oxidative degradation. Thus, these polymers and elastomeric material often require stabilization during melt processing. Exemplary stabilizers include phenolic antioxidants, hindered amine light stabilizers, ultraviolet light absorbers, organophosphites, antioxidants, metal salts of fatty acids, hydrotalcites, metal oxides, epoxidized oils, hydroxylamines, amine oxides, lactones, and thiosynergists.

Organophosphites are used broadly in the stabilization of polyolefins as non-discoloring antioxidants during melt processing, fabrication, and long term applications. Stabilization strategy of various polyethylene resins depends on the type (HDPE, LDPE, LLDPE, etc.), manufacturing process (gas-phase, slurry, solution), and catalyst (Ziegler-Natta. Chromium, metallocene, etc.) employed in the polymer production. Often times, the molar ratio of phosphite to hindered phenolics and the neutralizer package is dependent on the polymer grade. It is a common commercial practice to use combinations of sterically hindered phenols and phosphites in various molar ratios as a stabilizer system for polyethylene.”

[Zahalka, US Patent 8,258,214 (9/4/2012)]

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Copyright 2012 by Roger D. Corneliussen.
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* Date of latest addition; date of first entry is 5/24/2012.