Antioxidant is a kind of plastic additives that can effectively reduce the self-oxidation reaction rate of plastics and promote the degradation of plastics. Its application range involves almost all polymer products. Plastic antioxidants generally include phenolic antioxidants, phosphorus, sulfur auxiliary antioxidants, and metal ion passivators, etc. The types of applications and increase in them depend mainly on plastic materials, processing techniques and usage. Oxidants can be divided into three types according to their functions (main antioxidants, auxiliary antioxidants, and carbon-based self-trapping agents).

The antioxidant effects are as follows:

1. Synergy:

The well-known synergistic effect is that amine and phenolic antioxidants cooperate with peroxide decomposers to improve the heat resistance, oxidation resistance and anti-aging properties of the material. Collaboration includes inter-molecular coordination and intra-molecular coordination. Scott et al. proposed the concepts of uniform coordination and inhomogeneous coordination between molecules. The homogeneous synergistic effect is the synergistic effect between two compounds with the same mechanism but different activities, while the heterogeneous synergistic effect is the synergistic effect between two or more antioxidants with different mechanisms. This kind of internal coordination of molecules is called self-synergy, which is a kind of stabilizer containing multiple functional groups, which have a synergistic effect with each other.

The use of phenolic antioxidants and sulfur antioxidants at the same time has better long-term antioxidant effects than phenolic antioxidants used alone. Phosphorus antioxidants can decompose hydrogen peroxide and are mainly used as antioxidants during processing. Different processing temperatures have different processing stability. Phosphorus antioxidants are used at normal processing temperatures (near 200°C) (at high temperatures). Phosphorus antioxidants and phenolic antioxidants are used at the same time. Phenolic antioxidants can capture hydrogen peroxide and make phosphorus resistant Oxygen is more stable, thus exerting a synergistic effect. For example, when organic phosphoric acid is also used in the polymerization inhibitor phenolic antioxidant, the number of free radicals captured will be greatly increased.

2. Confrontation effect:

Some antioxidants can produce harmful effects when used in combination. This is the so-called antioxidant effect. Hindered amine compounds exhibit resistance that is incompatible with thiopropionate esters. There is also a certain antagonistic effect between polysulfides in rubber and certain antioxidants. Secondary aromatic amines and hindered alkyl phenols are effective composite antioxidants, but when they are combined with polyethylene containing carbon black (polyvinyl alcohol shielding agent), the antioxidant effect is better than that of polyethylene without carbon black. Together, they are worse because the surface of carbon black has a catalytic oxidation effect on amine or phenolic antioxidants.