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Despite their outstanding mechanical properties, plastic products are highly prone to degradation as a result of excessive exposure to harmful environmental factors, one of which is ultraviolet (UV) light. Hence, to maintain their good conditions, the application of UV stabilizers in plastic will be an ideal choice. So, what are these substances and how exactly do they benefit plastic products? Let’s find out in this article!

For most plastic products, especially those that are used outdoors, it is inevitable to be vulnerable to negative environmental effects such as ultraviolet (UV) light, oxygen, temperature,... The frequent exposure to those elements leads to the transformation in the chemical structure of polymers, resulting in the degradation of end products’ mechanical properties. 

1. Degradative impacts of UV light

UV light (also known as ultraviolet light) is a type of electromagnetic radiation with wavelength ranging from 290 nm to 400 nm. It accounts for approximately 10% of the total electromagnetic radiation released from the sun. The thing is, each type of polymer is sensitive to certain wavelengths within the 290-400 nm UV region. 

When being exposed to UV lights, certain components in a polymer (known as chromophores) will absorb UV radiation. This long-term process eventually breaks down the polymer chains, thus leading to the deterioration of physical properties. These may vary between different groups of polymers but normally include the loss of impact strength, changes in color, cracking, loss of elongation, tensile strength or chalking of the surface. 

Let’s take a plastic outdoor chair as an example. Under the effects of UV light, its color will be faded and spotted on the surface while the plastic itself becomes easily broken. In this case, the polymer's structure has been apparently changed, leading to the degradation in physical properties of the end-products. Hence, the application of UV stabilizers in plastic plays an indispensable part in the durability of your products. 

2. UV stabilizers in plastic: What are they and how many types do they have?

As one of the most effective solutions to the UV degradation of plastic, UV stabilizers are chemically formulated to absorb UV light’s energy, thus minimizing the contact between plastic surface and the UV rays. Normally, UV stabilizers are embedded into polymer combinations during the mixing phase to ensure it will disperses well on products' surfaces. Interestingly, there are at least 3 types of UV stabilizers in plastic, which differ from each other regarding the mechanism of action.  

Absorbers

Absorbers function by absorbing UV light, which may be absorbed by chromophores and change the harmful UV radiation into harmless infrared radiation or heat. Cost effective they might be, UV absorbers are most suitable for products with short-time exposure only. In the long run, this material is much less efficient. Some popular UV stabilizers of this type are: carbon black (which is the most common one thanks to its black color), rutile titanium oxide (which is effective in the 300 - 400 nm range but work less efficiently in the short wavelength ranging below 315), hydroxybenzophenone, hydroxyphenyl benzotriazole (this type is suitable for neutral or transparent applications but not very useful in thin parts below 100 microns), benzophenones for PVC, benzotriazoles and hydroxyphenyl triazine for polycarbonate, oxanilides for polyamides.

Quenchers

Another type of UV stabilizers in plastic are quenchers, which are also called light stabilizers. They work by quenching molecules that are over-excited during the UV absorption, and transfer the energy absorbed into heat. Generally, compared to its counterparts, quenchers are considered as the least effective methods of blocking UV radiation.

HALS

When it comes to the most effective UV stabilizers in plastic, HALS (Hindered amine light stabilizers) will undoubtedly be that one. Unlike its fellows, which work in the absorption phase of polymer, HALS take place in the early of the polymer degradation process. When free radicals are formed, it then traps them, thus preventing them from doing any damages to end-products. However, the chosen HALS must be compatible with the polymer, or else it can cause die build up at the extruder die and inefficient polymer protection. 

3. Common applications of UV stabilizers in plastic industry

Since those types of UV stabilizers work differently, they’re commonly added in polymer combinations in multiple ways. Here is how they are applied in some popular types of polymers. 

UV stabilizers for PP (Polypropylene)

Polypropylene is one of the most common types of polymers that are widely used in various applications such as raffia, extrusion,... However, its greatest disadvantage is the thermal sensitivity. As unstable species (hydroperoxides) and radicals can form during polypropylene’s processing, it strongly absorbs UV light when being exposed to the Sun. Hence, the application of UV stabilizers in PP is extremely important to end-products’ longevity. HALS is amongst the most commonly used UV stabilizers for PP products. 

UV stabilizers for PE (Polyethylene)

Though less sensitive than PP, PE also needs specific stabilizers against UV light. The chosen one varies between multiple types of PE. 

In HDPE tapes applications, a good retention of physical properties after light exposure is mostly required. Therefore, the combination of two types of HALS stabilizers, which is a low molecular mass HALS and a high one, is commonly used to improve the mechanical properties of HDPE tape applications. 

Whereas, the deterioration of products’ visible appearance (such as chalking, loss of gloss and cracks) is the main concern in HDPE injection moulding. In this case, the mixture of two types of HALS still can fulfill end-products’ requirements. Furthermore, the lightfastness of the pigment can be improved by the addition of a small amount of benzotriazole type UV absorber.

For LDPE blown film, things get more complicated as UV stabilizers in plastic films are required to increase the films’ service life. However, the use of chemicals (such as pesticides) in agriculture often considerably afflict the function of UV stabilizers since they mostly are sulfur and/or halogen-based compounds. Nickel organics, after a long period being used as a temporary solution, has been finally replaced due to its serious environmental impacts by the combination of high Mw HALS with a metal oxide and a stearate. 

UV stabilizers for HIPS (High impact polystyrene)

HIPS is a low cost plastic material that is specified for low strength structural applications (eg. covers, housings, signage, display items) when impact resistance, machinability, and low cost are required. The main requirement for UV stabilizers in this type is the retention of physical properties, which can easily be handled by the combination of UV absorber benzotriazole  and liquid low Mw HALS. 

4. Selection criteria of UV stabilizers

As we already discussed, there are different types of UV stabilizers in plastic and specific requirements for each type of resins. These below are key criteria needed consider carefully before making up your mind:

• Environment: Anti UV additives are formulated in accordance with the specific climate conditions that end-products are exposed to. 
• End-product properties: As each product has different physical characteristics, the chosen UV stabilizers must be completely compatible with the current components in order to achieve the best result.
• Color: Pigments are vital components in almost every type of plastic product. Since each color has a different level of sensitivity to UV light, the stabilizers added must be fitted to the color characteristics to ensure it disperses well on the plastic surface. 
• Product’s life cycle: As mentioned above, the protection capacity varies among three types of UV stabilizers. HALS can be active for the longest period, while the others only work sufficiently in the short term. Thus, plastic enterprises should consider carefully to find the light additives that suit them best. 

5. EuroPlas UV stabilizers in plastic

With nearly 14 years of experience in the plastic material market, EuroPlas products have been available in over 80 countries worldwide. Plastic additives, especially UV stabilizers are one of our best sellers, which have won the trust of millions of customers. Most importantly, all of our products are tailor made based on customers’ requirements, making each output become a perfect right fit for your end-products.

For further details and consultation, don’t hesitate to contact us!