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Antioxidants are used to protect polymers from oxidative degradation during processing and while in use.  Antioxidants can be both primary antioxidants and secondary antioxidants. 

Primary Antioxidants

  • Sterically hindered phenols (e.g., BHT) trap peroxy radicals by acting as hydrogen donors. Most are higher in molar mass than BHT so as to reduce volatility and migration.
  • Aromatic amines act as hydrogen donors but can cause discoloration, so they are primarily used in rubbers materials.

Secondary Antioxidants

  • Some (e.g., phosphite secondary antioxidants) transform hydroperoxides to stable products while others, such as thiosynergists, decompose hydroperoxides.

Alkyl Radical Scavengers

  • Alkyl radical scavengers interact with alkyl radicals which could otherwise lead to degradation of the plastic. This includes HALS (Hindered Amine Light Stabilizers, which also promote light stability), hydroxyl amines, benzofuranones.

Light stabilizers are used to protect polymers from degradation by UV light. This class includes UV Absorbers and HALS.

UV Absorbers

  • These additives absorb UV energy that could otherwise lead to breakdown of the polymer. Examples include 2-hydroxybenzophenones and 2-hydroxybenzotriazoles.

HALS (Hindered Amine Light Stabilizers)

  • These additives scavenge free radicals.  They are usually of higher molar mass and can regenerate, thereby providing long-term thermal and light stability.

  • Approach

    HALS are measured using size exclusion chromatography with photodiode array detection (SEC-PDA). 

    Phenolic antioxidants are measured using a reverse phase high performance liquid chromatography (HPLC) method.  This method is based on ASTM D6042, “Standard Test Method for Determination of Phenolic Antioxidants and Erucamide Slip Additives in Polypropylene Homopolymer Formulations using Liquid Chromatography (LC).”

  • Sample Considerations

    Generally, at least 100 mg is required per method.  Methods cannot identify materials other than those included in the standards mixture. We ecourage you to talk with our experts today and request a quote. 

  • Experience

    We have decades of experience analyzing materials and finished products for polymer stablizers. Some examples of our experience include:

    • Verification of specific stabilizers in products
    • Competitor product deformulation/reverse engineering to determine additives
    • Confirmation of the levels of additives in a consumer product which was degrading too quickly