December 25, 2023 Longchang Chemical

Which kinds of antioxidants are there? Classification of common antioxidants

According to the actual role of the different mechanisms of influence, antioxidants can be grouped into the following categories:
1, the main antioxidants

The results show that the degradation aging process is a free radical chain reaction. These materials are heated and sheared to emerge free radicals, and when exposed to oxygen, they will transform into peroxide radicals, which further remove hydrogen atoms from the polymer backbone to form relatively stable polymer-based hydrogen peroxide. The chain grows and then the reaction expands.
By providing hydrogen atoms or electrons, hydrogen-based antioxidants, called primary antioxidants, are consumed by consuming the peroxide radicals, thereby terminating the chain reaction. Typical primary antioxidants are also included in this process.
Aromatic amine antioxidants: a kind of antioxidant with long history and only be used in dark-colored products, especially some rubber and polyurethane products due to tintage property.
Hindered phenolic antioxidants: The most widely used class of primary antioxidants. Many famous brand, such as antioxidant 1010, antioxidant 1076 etc, all belong to this category.

2, auxiliary antioxidants

An antioxidant that can react with the hydroperoxides produced in the above chain reaction and decompose them into stable substances, thus terminating the chain reaction, known as auxiliary antioxidants.
Phosphite is the most widely used auxiliary production antioxidant, typical products such as 168.
Sulfide is another auxiliary antioxidant.

3, both primary and secondary function of the antioxidant

Antioxidants that can react with peroxides and eliminate hydrogen peroxide, which makes itself has high efficiency. A typical example is hydroxylamine.

4、Metal antioxidants

Metal passivators can form stable coordination reacting with metal ions, especially copper ions. In polymers contacting with metals, such as wires and cables, metal passivators can significantly improve the stability of the polymer.
Different types of antioxidants can be used in combination and have a synergistic effect. That is, the total effect of the combined use of two stabilizers is higher than the sum of the effects of the two stabilizers used alone. The most representative is the combination of hindered phenol and phosphite antioxidants.

What should be noted when selecting antioxidants?

Heat and light stabilizers matches with antioxidants is significant. Then think about the use of most antioxidants, there are concentrations that fits them. Within this scale, there will be a blurring effect as the antioxidant dose increases beyond this scale. The adding amount of antioxidant depends on a number of factors such as the nature of the plastic, the efficacy of the antioxidant, synergistic effects, the conditions of application of the product, and the production cost. Usually amine antioxidants are more active than phenolic antioxidants, so they should have greater antioxidation, but the former will change color under the action of oxygen and exposed on lights and most of them are colored and toxic, so they should be stable applied in plastics. The priority is the cooperation of antioxidants.

(1) Additive effects

The combination of various antioxidants can play their respective characteristics and effects to increase the overall effect. For example, when hindered phenols with different degrees of evaporation or spatial site resistance are used together, their antioxidant effects can develop over a wide range of temperatures and the effect is enhanced. If only one antioxidant is used in the formulation, its dosage must be much larger, but its not feasible that high concentrations can cause violent oxidative reactions. However, when several low-concentration antioxidants are used together, which can not only meet the basic demand, but also prevent strong oxidation.

(2) Synergistic effect.

When two main antioxidants with different activities are used at the same time, hydrogen atoms are free from high-activity antioxidant to hinder the oxidizing active chain, while the low-activity antioxidant replenishes hydrogen atoms for the high-activity antioxidant for regeneration as well as long-lasting antioxidant effects with good performance.
When the main and auxiliary antioxidants are used together, synergistic effect should be noted. If the main antioxidant just releases hydrogen atoms, the hydrogen atoms will convert the free radicals of peroxides into hydroperoxides stopping the chain reaction, and then the hydroperoxides combine with the peroxide effect of the antioxidant to produce an inactive and stable issue. Thus the rate of oxidation reaction is greatly reduced and the antioxidant effect is increased.
A development of antioxidant molecular structure with the following two or two based on more than the different social stability function, called self-synergistic effect, for example, sulfur-containing hindered phenolic antioxidant, it has a chain reaction for stopping agents and peroxides can be divided into two layers of the design of the effect of the agent, this kind of production of antioxidant can strengthen the effect of antioxidant.
As antioxidants matches with heat and light stabilizers, try to select antioxidants with strong synergistic effects avoiding the opposite one.

 

Application of antioxidants

An antioxidant is a substance that prevents and resists the oxidizing process of a substance. There are various types, ranging from low to high molecular weights, natural and synthetic.

Primary Antioxidants
Typical primary antioxidants include the following two categories.

Aromatic amine antioxidants:Amines antioxidants are almost all derivatives of aromatic secondary amines, mainly including diaryl amines, p-keto amines and aldehyde amines. Most of them have good antioxidant effects, but prone to discoloration, and commonly used in the rubber industry and polyurethane products.
Hindered phenol antioxidants: common antioxidants. The antioxidant efficiency is generally weaker than amine antioxidants, but no pollution generated, mainly used in plastics and light-colored rubber products, many types such as antioxidant 1010 and antioxidant 1076.

Auxiliary antioxidants

Two main categories are thioesters such as thiodipropionate and phosphite esters. They are mainly used in polyolefins, and combine with phenolic antioxidants to tragger a synergistic effect.
Phosphite is a widely used auxiliary antioxidant, typical one is 168.
Sulfides are another kind of auxiliary antioxidant, such as DLTDP and DSTDP.

Metal Passivators

When polymers contact with heavy metal, the catalytic effect of the heavy metal ions causes a degradation reaction in the polymer. For example, copper, the cable materials in the core wire will be damaged due to this reaction. Adding copper ion passivators can greatly improve the stability of the polymer.

Which application fields of Antioxidants?

Polyolefins: polypropylene, polyethylene, ethylene-vinyl acetate copolymer, LLDPE
Styrene: ABS, polycarbonate/ABS, IPS, GPPS
Elastomers: Styrene-Butadiene Rubber (SBR), Polybutadiene Rubber (PBR), Ethylene-Propylene Rubber (EPDM), SBS/SRS, Thermoplastic elastomers.
Polyvinyl chloride: PVC
Polyurethane: RIM, TPU
Engineering plastics: polycarbonate and polymethyl methacrylate.

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