Plastic antioxidants are a group of chemicals that slow down the process of oxidation in plastic. Oxidation causes a chemical reaction that produces free radicals—oxygen-containing atoms with an odd number of electrons. Free radicals cause chain reactions that damage the polymer molecules in plastic, degrading their strength and appearance. Antioxidants stop these chain reactions by removing free radicals and inhibit further oxidation by reacting with oxygen to form more stable end products. They are added to plastics during the manufacturing process to reduce the effect of thermal oxidation induced by processing temperatures.
Antioxidants protect plastic surfaces from UV damage, making them essential for outdoor applications. The antioxidant is usually added in small amounts to the base resin, although it can also be applied as a coating or surface treatment to improve the lifespan of a plastic part.
Antioxidants are often used with stabilizers, which prevent degradation caused by ultraviolet light (UV). Although many plastics offer UV resistance, they can deteriorate over time when exposed to sunlight or artificial UV light sources. Additives are known as UV stabilizers that protect against degradation by absorbing UV light and dissipating it as harmless heat.
Many of the common antioxidants used in plastics are those that have been around for a long time. Some of the most commonly used antioxidants include phenolic antioxidants, such as Irganox 1010 and Irganox 1076. These are used in high-density polyethylene and polypropylene composites. The latter is also used with other materials, such as polyvinyl chloride and ethylene vinyl acetate.
Another class of antioxidants is an amine, which includes Irganox 1098 and Irgafos 168. One of the most widely used antioxidants today is calcium carbonate. It is used in thermoplastics and thermosets, as well as elastomers, to prevent thermal oxidation and hydrolysis of metals.
1. Phenolic antioxidants:
Phenolic antioxidants are the most widely used type of antioxidant. They are mainly used in polyethylene, polypropylene, engineering plastics, synthetic rubber, and other products.
2. Heterocyclic amines:
Heterocyclic amines can also be used as antioxidants for some plastics. It is mainly used in products such as polyolefins and ABS resins.
3. Phosphite esters:
Phosphate esters are used as stabilizers for many kinds of plastics and elastomers. The product has good compatibility with the resin and can be used to produce transparent plastic products with excellent anti-aging properties. It is mainly used in products such as PVC and polystyrene.
The addition of antioxidants to the plastic products can prevent the thermal oxidation reaction in the melt and also can delay the oxidation degradation of plastics in use so as to improve the thermal stability of plastic products.
With the continuous development of product technology, people’s requirements for product quality are getting higher and higher. The use of antioxidants for plastic products is no longer limited to the prevention and inhibition of thermal oxidation reactions. People pay more attention to improving product performance, prolonging product life, and environmental protection. Therefore, in order to obtain high-quality plastic products, it is necessary to choose suitable antioxidants according to different materials and use conditions.
The selection of antioxidant additives is mainly affected by four factors:
The first factor is that different plastics have different antioxidant effects on different types of plastics due to their own chemical structure;
The second factor is that the use condition of plastic products in different climates has a great influence on the anti-aging effect;
Thirdly, different antioxidants have different functions in preventing heat aging, light aging, and weather resistance;
Fourthly, the cost factor affects the choice of antioxidants.
How Do Plastic Antioxidants Work?
Antioxidants are substances that prevent oxidation (the primary cause of deterioration) in other substances. Oxidation causes plastics to break down, so antioxidants slow this process, keeping plastic parts intact.
There are different types of antioxidants, and they work in different ways, depending on the type of plastic being treated. For example, some antioxidants work by filling the spaces between polymer chains in plastic and preventing them from being broken apart by light or heat. Antioxidants can also act as free-radical scavengers. Free radicals are atoms that contain unpaired electrons, which makes them highly reactive. Free radicals can damage plastics through a process called chain scission, where the bonds between polymer chains are broken, causing deterioration to occur more rapidly.
The price of plastic antioxidants is mainly affected by the type and dosage. For example, a good stabilizer for polypropylene (antioxidant 1010) is about 18-20 yuan per kilogram, and the price of a high-quality polystyrene stabilizer (antioxidant 168) is about 15-16 yuan per kilogram; the stability of polystyrene depends on the antioxidant 168, so its dosage is higher than that of polypropylene, which determines its price.
Yes. And it is not only the antioxidants that matter but also the stabilizers, colorants, and other additives. The good news is that the degradation is usually slow and can be predicted.
The degradation mechanisms of plastics are mostly hydrolysis, oxidation, and photodegradation. For example, polypropylene (PP) will start to visibly degrade in about five years if exposed to sunlight for long periods of time. However, a plastic item like a bucket can retain its physical strength for up to 20 years or more if stored in a dark place and at room temperature.
Antioxidants generally fall into two types: primary antioxidants and secondary antioxidants. Primary antioxidants are free radical scavenging compounds that stop the oxidation of plastic by reacting with free radicals generated during degradation. Secondary antioxidants are chain-breaking compounds that react with peroxy radicals generated during the initiation of oxidation by a primary antioxidant or another radical source such as an impurity or light.