How to choose the right UV absorber for your polymer

Not all UV absorbers work equally well in all polymers. Choosing the wrong one can result in poor protection, processing problems, colour impact or migration. The right choice depends on the polymer you are working with, the processing conditions and what the end product needs to withstand. Here is what to consider.

Polymer type

The starting point is always the polymer. Different polymers have different chemical structures, processing temperatures and sensitivities to UV radiation. A UV absorber that works well in polycarbonate may not be compatible with polypropylene or PVC.

Polycarbonate and engineering resins such as ABS, PET and polyamide are typically protected with benzotriazoles or hydroxyphenyl triazines (HPT). These offer broad-spectrum UV-A and UV-B absorption and are stable at the high processing temperatures these polymers require.

Polyolefins such as polyethylene and polypropylene are often protected with benzophenones or benzotriazoles. These polymers are used in a wide range of outdoor applications and need UV absorbers that are compatible with the non-polar polymer matrix.

PVC requires UV absorbers that are compatible with the plasticisers and other additives in the formulation. Benzophenones are commonly used in flexible PVC applications.

Polyurethane, both rigid and flexible, can yellow through a different mechanism than most thermoplastics. This is discussed further below.

Processing temperature

UV absorbers must remain stable during processing. If the processing temperature exceeds the thermal stability of the absorber, it will degrade before it has a chance to protect the polymer.

HPT UV absorbers such as Omnistab UV 1600 are specifically designed for high-temperature processing, remaining stable above 300°C. This makes them suitable for engineering plastics processed by injection moulding or extrusion at high temperatures.

Benzophenones have lower thermal stability and are better suited to polymers processed at lower temperatures, such as flexible PVC or certain polyolefin applications.

UV wavelength range

Different UV absorbers absorb at different wavelengths within the UV spectrum. Knowing which wavelengths are most damaging to your polymer or coating helps narrow down the right choice.

Benzotriazoles and HPT absorbers cover both UV-A (315–400 nm) and UV-B (280–315 nm) ranges. This broad-spectrum coverage makes them suitable for outdoor applications where both ranges are present.

Benzophenones absorb primarily in the UV-A range. They are useful where UV-B exposure is limited or where the primary concern is visible light-induced yellowing rather than photodegradation.

Film thickness and concentration

UV absorbers work by absorbing UV radiation as it passes through the material. Thicker materials provide more opportunity for the absorber to do its work, so they can function well at lower concentrations. Very thin films require higher concentrations or a different approach.

For thin films, HALS may be more appropriate than UV absorbers, or a combination of both may be needed. The relationship between concentration and protection is not always linear, and testing in the specific application is always recommended.

Polyurethane and yellowing

Polyurethane yellowing is a specific issue that comes up frequently. Aromatic polyurethanes yellow through a different mechanism than most other polymers. The aromatic groups in the polymer chain absorb UV radiation and oxidise, producing yellow-coloured compounds.

Non-yellowing polyurethanes use aliphatic isocyanates instead of aromatic ones, which do not have this yellowing mechanism. For aromatic PU systems where some yellowing is expected, antioxidants combined with UV absorbers can slow the process. For water-based PU coatings, UV absorbers that are compatible with the aqueous system and stable during drying are required.

Combining UV absorbers with HALS

For applications requiring long-term outdoor performance, UV absorbers are usually combined with HALS. UV absorbers handle the incoming UV radiation. HALS neutralise the free radicals that form when some UV damage does occur despite the absorber’s presence.

The combination provides more complete protection than either product alone and is standard practice for demanding outdoor applications such as automotive coatings, agricultural films and construction materials.

For more on how UV absorbers work, read our article on how UV radiation damages plastics. For an overview of which industries rely on UV protection, see our article on UV absorbers across industries.