Why UV absorbers are not suitable for thin plastic products?

Light stabilizers are divided into two types: HALS (hindered amine light stabilizers) and UV absorbers. HALS are used to prevent the chain breaking of plastics under light by capturing free radicals, thus ensuring the service life of plastics. Ultraviolet absorbers, on the other hand, absorb the energy of sunlight irradiated into plastics to prevent plastics from aging.

When polymer materials are used outdoors, they are degraded by ultraviolet (UV) radiation, heat, oxygen, and metal ions. This degradation results in yellowing, reduced gloss, embrittlement, cracking, and other physical and mechanical property changes. To fully preserve the functions of polymers and extend product life, ultraviolet absorbers, and light stabilizers must be added to resist UV light degradation reactions and enhance weather resistance.

Light stabilizers and UV absorbers have different functions in protecting polymer materials from weathering and aging. While UV absorbers belong to physical protection, light stabilizers act as free radical capture agents in the recycling process. The efficacy of light stabilizers and UV absorbers is related to factors such as the molecular structure, polarity, thickness, density, acidity, and alkalinity of the protected organic products, pigments, and fillers. Different types of light stabilizers and UV absorbers need to be selected according to the other materials to be protected.

In layman's terms, light stabilizers maintain the light stability of the product by participating in photochemical reactions, while ultraviolet absorbers absorb incoming light. However, the absorption bands of different UV absorbers are different, and UV absorbers require a certain thickness to work better. Therefore, only light stabilizer can be used for thin products, while UV Absorber + light stabilizer is recommended for thick products.

Why is it not recommended to use UV absorbers for thin products?

The absorption of ultraviolet light is governed by the Lambert-Beer law, which requires a high concentration of absorber and sufficient polymer thickness to obtain better absorption and effectively delay photodegradation. Therefore, UV absorbers are only effective if:

◆Protecting thick polymers,

◆Contents with added UV absorbers,

◆When protecting other additives that are more sensitive to UV light (e.g. pigments and flame retardants)

◆Plastic substrates with UV-absorbing functional groups like polystyrene and polyester.

UV absorbers are not effective at protecting very thin items such as films/fibers. This is determined by the light absorption law Lambert-Beale law for the thickness of the article, while hindered amine light stabilizers inhibit polymer degradation

Light stabilizers are very effective stabilizers for polymers, especially polyolefins. They do not absorb ultraviolet radiation, but act as inhibiting polymer degradation. Significant stabilization levels are reached at relatively low concentrations. The high efficiency and long life of light stabilizers are due to cycling processes in which light stabilizers are regenerated during stabilization rather than consumed.

Cyclic process - light stabilizer regeneration

Therefore, light stabilizers are very effective in high surface area applications such as films and fibers, and they are an efficient additive for light stabilization of polyolefins. Additionally, efficient heat stabilizers can extend the service life of polyolefin products.

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