One of the greatest benefits of using plastics is their longevity. However, when certain polymers are exposed to unfavourable conditions, such as extreme heat or exposure to certain chemicals, they will break down more quickly. For plastics used in automotive injection moulding and thermoforming, we use plastics with added antioxidants to extend their service life and durability. But what do antioxidants do to plastics? Are they the same as the antioxidants found in vitamins?
First, let us define the terms we will use to describe this process. Free radicals are uncharged, unstable molecules that are constantly produced through oxidation (a chemical reaction that moves electrons away from existing molecules). Rust is produced when iron reacts with oxygen and the iron molecule loses electrons while the oxygen gains them. Apples turn brown because the fruit enzyme polyphenol oxidase reacts with the oxygen in the air.
Plastic Antioxidants
In the human body, oxidation occurs through metabolism, a process that is accelerated when exposed to toxins such as tobacco smoke, which over time can damage cells, accelerate the ageing process and even increase the risk of cancer. In plastics, heat and chemical exposure can accelerate the oxidation process.
This is where antioxidants come into play. Antioxidants neutralise free radical molecules, accelerating oxidation and causing damage. You may have heard of healthful antioxidants - vitamin C, beta carotene and lycopene are examples of powerful antioxidants found in food that we can consume to slow the attack of free radicals on our cells. If you dip a chopped apple into lemon juice, it will not turn brown quickly because vitamin C slows down the oxidation process that I neutralises free radicals.
Antioxidant 1010 CAS 6683-19-8
Plastic antioxidants have been widely used in plastics. Polyolefins and ABS are the most used, followed by POM, PVC and nylon. The use of two or more antioxidants should be considered at the same time to produce the advantages of additive or synergistic effects to obtain better results.
①Additive effect: The main antioxidant and the auxiliary antioxidant, when used together, bring out the characteristics of each and are better than using them alone. The use of high concentrations of antioxidants can cause side effects. But when several low concentrations of antioxidants are taken out, the side effects can be prevented and can also have a superimposed effect.
(2) Synergistic effect: When antioxidants are used properly, their combined performance can exceed the effect of their individual use. It is known as the synergistic effect.
Antioxidant 1076 Cas 2082-79-3
Finally, the stability to oxygen varies between different plastics, so some plastics do not have antioxidants added. Others must have antioxidants added. Plastic antioxidants are used to trap the activity of free radicals and thus interrupt the chain reaction. Their purpose is to slow down the oxidation process and the rate of plasticisation. By the mechanism of action of antioxidants, it can affect all plastics.
There are two main types of antioxidants used in plastics.
Primary antioxidants: known as "chain-breaking antioxidants", they are free radical scavengers that remove alkyl radicals and hydroxyl radicals produced from abstract hydrogen when polymer chains are broken at high temperatures; examples include hindered phenols.
Secondary antioxidants: these remove organic hydroperoxides formed when primary antioxidants remove free radicals. If not removed, hydroperoxides can cause new free radical reactions. Examples include phosphites and thioethers.
Often, a mixture of primary and secondary antioxidants work together to achieve superior processes. In injection moulding, phosphite stabilises the plastic during the melting process, while thioether is ideal for the heat to which the plastic is often exposed during use.
Anti-ozone agents can also prevent and slow down polymer degradation caused by ozone. This is more likely to affect rubber, as ozone can cause cracking, but it can also affect plastics.
