When we come into contact with plastics or other polymers, we often hear about antioxidants. You may also roughly understand that adding antioxidants is for anti-oxidation and anti-aging, but many friends may not understand the mechanism. Today, we will learn together the causes, mechanisms and solutions to the aging of polymer materials.
What is oxidation?
Professional explanation: Oxidation, in a narrow sense, means the chemical reaction between oxygen and other material elements. It is also an important chemical unit process. Oxidation in a broad sense refers to the process in which a substance loses electrons (the oxidation number increases).
Popular explanation: yellowing, aging, hardening, brittleness, softness, darkness, etc. caused by wind, sun, rain, oxygen in the air, water, and wind erosion. Rust and other phenomena can be roughly classified as oxidation.
The best example is the phenomenon of a cut apple gradually turning yellow after being exposed to the air for a period of time. In fact, not only apples will oxidize, but our skin will also oxidize. Plastic products and high molecular polymers will oxidize and age! Aging is a ubiquitous process in nature. The most common process around us is the process of life from birth, growth, and aging, which is the most typical aging process. .
The corrosion of metal materials is also a kind of aging, from shiny objects to rusty objects until they lose their use value.
The same is true for polymers. During processing and use, due to the combined effects of environmental factors such as heat, oxygen, water, light, microorganisms, and chemical media, polymers The chemical composition and structure of materials will undergo a series of changes, and the physical properties will also deteriorate accordingly, such as becoming hard, sticky, brittle, discolored, losing strength, etc. These changes and phenomena are called aging.
What harm will occur if molecular polymers age?
1. Reduce mechanical properties
2. Fading
3. Reduce transparency
4. Yellowing and aging
5. Cracks
6. Odor (alcohols, aldehydes, ketones)
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What factors are causing the aging of polymers?
1. Polymer structure: double bonds and benzene rings are not stable enough, which can easily lead to polymer decomposition and yellowing
2. Residual impurities in polymer synthesis: peroxides and metal ions lead to polymer degradation and yellowing
3. Oxygen (air): The presence of oxygen and ozone causes the decomposition of polymers
4. Energy: mechanical stress, heat, ultraviolet rays
5. Air pollution: NOx, SOx.
6. Water and moisture: may cause dissolution and precipitation of organisms: degradation caused by biological enzymes
Why do polymers age?
High molecular polymers will form excited state molecules under the action of heat or light. When the energy is high enough, the molecular chains will break to form free radicals. The free radicals can polymerize A chain reaction is formed inside the material, which continues to cause degradation and may also cause cross-linking. The culprit: free radical R·
If oxygen or ozone is present in the environment, a series of oxidation reactions will be induced to form hydroperoxides (ROOH), which will further decompose into carbonyl groups.
If there are residual catalyst metal ions in the polymer, or metal ions such as copper, iron, manganese, cobalt, etc. are introduced during processing and use, the oxidation of the polymer will be accelerated. degradation reaction. High molecular polymer can prevent aging.
So, antioxidants have become a life-saving elixir for the materials industry!
In order to prevent the polymer from aging, it can isolate light and heat, and the most important thing is to add antioxidants! ! Then here comes the point! Where can I find efficient, authentic, and good-quality antioxidants?
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