Antioxidants are a type of plastic additives that can effectively reduce the auto-oxidation reaction rate of plastic materials and delay the aging and degradation of plastic materials. Its applications involve almost all polymers. products. Antioxidants for plastics usually include phenolic antioxidants, phosphorus and sulfur auxiliary antioxidants, and metal ion passivators. The application types and amounts of antioxidants are mainly determined by the different plastic materials, processing techniques and uses. Decide. Oxidants can be classified into three categories according to their functions (primary antioxidants, auxiliary antioxidants, and carbon free radical capture agents).
The interaction of antioxidants is as follows:
1. Synergistic effect:
Amine and phenolic antioxidants cooperate with peroxide decomposers to improve the heat resistance and oxidation resistance of the material. and anti-aging properties, which are well known synergistic effects. Synergy includes intermolecular synergy and intramolecular synergy. Scott et al. proposed the concepts of uniform synergy and non-uniform synergy of intermolecular synergy. Uniform synergistic effect is the synergistic effect between two compounds with the same mechanism but different activities; non-uniform synergistic effect is the synergistic effect between two or several antioxidants with different mechanisms. Intramolecule synergy is called self-synergy, which is a stabilizer containing multiple functional groups that have synergistic effects with each other.
When phenolic antioxidants and sulfur antioxidants are used together, they have higher long-term oxidation prevention effect than when phenolic antioxidants are used alone. Effect. Phosphorus antioxidants can decompose hydrogen peroxide and are mainly used as antioxidants during processing. Due to different processing temperatures, processing stability varies. Phosphorus-based antioxidants are used at normal processing temperatures (near 200°C). At high temperatures, phosphorus-based antioxidants and phenolic antioxidants are used together. The phenolic antioxidants can capture hydrogen peroxide, making the phosphorus The antioxidants are more stable and thus exhibit a synergistic effect. For example, when an organic phosphate is used in combination with a polymerization-inhibiting phenolic antioxidant, the number of free radicals captured can be greatly increased.
2. Antagonistic effect:
When some antioxidants are combined together , will produce harmful effects, which is called the antagonistic effect of antioxidants. Hindered amines are incompatible with thiodipropionate due to their alkaline nature and exhibit antagonistic effects. There are also antagonistic effects between polysulfides in vulcanized rubber and certain antioxidants. Secondary aromatic amines and hindered alkyl phenols are effective complex antioxidants, but when they are added to polyethylene containing carbon black (UV screener), their antioxidant effect is worse than that of polyethylene without carbon black. The reason is that the surface of carbon black has a catalytic oxidation effect on amine or phenolic antioxidants.
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