Polymer stabilizers (British: polymer stabilisers) are chemical additives which may be added to polymeric materials, such as plastics and rubbers, to inhibit or retard their degradation.
Common polymer degradation processes include oxidation, UV-damage, thermal degradation, ozonolysis, combinations thereof such as photo-oxidation, as well as reactions with catalyst residues, dyes, or impurities.
All of these degrade the polymer at a chemical level, via chain scission, uncontrolled recombination and cross-linking, which adversely affects many key properties such as strength, malleability, appearance and colour.
Stabilizers are used at all stages of the polymer life-cycle. They allow plastic items to be produced faster and with fewer defects, extend their useful lifespan, and facilitate their recycling. However they also continue to stabilise waste plastic, causing it to remain in the environment for longer.
Many different types of plastic exist and each may be vulnerable to several types of degradation, which usually results in several different stabilisers being used in combination. Even for objects made from the same type of plastic, different applications may have different stabilisation requirements. Regulatory considerations, such as food contact approval are also present. A wide range of stabilizers is therefore needed.
The market for antioxidant stabilisers was estimated at US1.69billionfor2017,withthetotalmarketforallstabilizersexpectedtoreachUS5.5 billion by 2025.
Antioxidants inhibit autoxidation that occurs when polymers reacts with atmospheric oxygen. Aerobic degradation occurs gradually at room temperature, but almost all polymers are at risk of thermal-oxidation when they are processed at high temperatures. The molding or casting of plastics (e.g. injection molding) require them to be above their melting point or glass transition temperature (~200-300 °C). Under these conditions reactions with oxygen occur much more rapidly. Once initiated, autoxidation can be autocatalytic.
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Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptability, plus a wide range of other properties, such as being lightweight, durable, flexible, and inexpensive to produce, has led to its widespread use. Plastics typically are made through human industrial systems.
Photodegradation is the alteration of materials by light. Commonly, the term is used loosely to refer to the combined action of sunlight and air, which cause oxidation and hydrolysis. Often photodegradation is intentionally avoided, since it destroys paintings and other artifacts. It is, however, partly responsible for remineralization of biomass and is used intentionally in some disinfection technologies. Photodegradation does not apply to how materials may be aged or degraded via infrared light or heat, but does include degradation in all of the ultraviolet light wavebands.
Polymer degradation is the reduction in the physical properties of a polymer, such as strength, caused by changes in its chemical composition. Polymers and particularly plastics are subject to degradation at all stages of their product life cycle, including during their initial processing, use, disposal into the environment and recycling. The rate of this degradation varies significantly; biodegradation can take decades, whereas some industrial processes can completely decompose a polymer in hours.
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