What is an antioxidant? Those conditions are what it must have

Antioxidants are a class of chemicals that, when present in small amounts in a polymer system, retard or inhibit the oxidation of the polymer, thereby preventing aging of the polymer and extending its useful life. Anti-aging agent." For engineering plastics processing, antioxidants can prevent thermal oxidative degradation during processing of certain polymers (such as aBS, etc.), allowing the molding process to proceed smoothly. The amount of antioxidant added is generally only 0.1-0.5 parts.

Ideal antioxidants

The ideal antioxidant should have the following conditions: 1 should have high antioxidant capacity: 2 good compatibility with the resin, no precipitation; 3 good processing performance. It does not volatilize or decompose at the processing temperature of the polymer; 4 has good resistance to extraction and is insoluble in water and oil; 5 itself is preferably colorless or light. To not pollute the product; 6 non-toxic or low-toxic; 7 low price.

In fact, any kind of antioxidant can not fully meet these conditions. Therefore, in actual use, according to the type, use and processing method of engineering plastics, the length of various additives is used together to produce synergistic effects.

With the development of engineering plastics industry, the use of antioxidants is increasingly widespread, and the demand is increasing. At present, engineering plastics widely used in antioxidants are polyamide, polyoxymethylene, aBS, etc.

Mechanism of action of antioxidants

According to the thermal oxidation mechanism of polymers, unstable radicals and hydroperoxides generated during thermal oxidation are the main factors causing deterioration of material properties. The mechanism of action of antioxidants is to terminate active radicals and decompose hydrogen. Peroxide. The free radical inhibitor with the inhibition of free-chain reaction is called the main antioxidant. It contains two series of amines and phenols. It is mainly used as phenolic antioxidant in engineering plastics. Hydroperoxide decomposers with decomposition hydrogen peroxidation are called auxiliary antioxidants, mainly including thioesters and phosphites, usually combined with primary antioxidants.

(1) Mechanism of action of primary antioxidants

The OH and ·NH contained in the phenolic and amine antioxidants can interact with the free radicals formed in the autocatalytic oxidation reaction, eventually causing the free radicals to disappear, and the oxidative chain reaction is terminated:


(R--resin molecular chain main body; R'——antioxidant structure main body)

R'H bucket R·a RH+R'


R' · ten R' · one R'R'

(2) Mechanism of action of auxiliary antioxidants

Phosphite antioxidants can decompose the hydroxide formed during the oxidation reaction into an inactive product, rendering it inactive:


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