Antioxidants

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Antioxidants are key ingredients in the compounding of polyethylene (PE) and polypropylene (PP) due to the limited stability of polyolefins to high temperatures and ultraviolet (UV) light.
Polymers exposed to air undergo oxidative degradation. They are processed at high processing temperatures, which initiate thermal oxidative degradation and a loss of physical properties. Resistance to thermal oxidation is one factor directly determining the commercial success of any polymeric material. Degradation during both processing and actual service life may cause irreversible changes to the polymer backbone. This is reflected in a loss of physico-chemical properties. Inhibition of oxidation by molecular oxygen is important in polyolefins during processing and fabrication, as well as for its long-term stability.

In polymer stabilisation technology, the combination of antioxidants with other stabilisers produces a synergistic stabilising effect. Antioxidants are used in polymers at low concentration levels during compounding (<1%). Depending on usage, these help to determine the long-term stability of the polymer and consume antioxidants over time. Polyolefin stabilisation is carried out with antioxidants such as a phenolic antioxidant (a primary stabiliser/radical quencher) or dialkyl-dithio-propionate or tris-alkyl-phenyl-phosphite (a secondary stabiliser/hydroperoxide decomposer). Polyamides are also stabilised by antioxidants. However, dialkyl-dithio-dipropionates are not used because of their relative volatility and intrinsic lower resistance to thermohydrolysis during processing. The addition of small amounts of mixtures of copper acetate and potassium iodide is used with polyamide to enhance the efficiency of the antioxidant .