Is rubber UV-resistant?

The UV resistance of rubber describes how well an elastomer resists sunlight, oxygen, and ozone without becoming brittle, tearing, or losing its elasticity. Rubber is not inherently UV-resistant; rather, depending on its chemical composition, it is more or less resistant. In particular, the number of double bonds in the polymer backbone influences whether free radicals can form under UV exposure. EPDM, Silicone (VMQ), FKM and Butyl rubber (IIR) are considered UV and ozone resistant, while rubber types with double bonds such as Natural rubber (NR), SBR and NBR Without protective additives, they quickly deteriorate in outdoor use.

Why does UV radiation damage rubber?

UV radiation triggers the formation of radicals in the polymer, which react with oxygen and cause oxidation by incident light (photooxidation). Depending on the elastomer, this leads to chain cleavage, resulting in a soft and sticky material (NR), or to post-crosslinking with curing and hardening (SBR, NBR). The damage begins at the surface and is manifested as discoloration, cracking, fine mesh lines, and a loss of tensile strength and elongation. In outdoor use, ozone directly attacks the double bonds of unsaturated rubber and causes cracks perpendicular to the stretching direction. However, this only occurs when the component is subjected to tensile stress above a material-dependent critical strain. UV aging and ozone aging are therefore two different mechanisms that usually occur together in seals and profiles outdoors.

Which rubber materials are UV-resistant?

Elastomers with saturated main chains offer hardly any points of attack against UV and ozone. Therefore, they are used for window profiles, roof seals, facade and exterior seals. Unsaturated rubbers such as NR, SBR and NBR are stabilized for outdoor use with UV inhibitors. Carbonite protects black rubber compounds by absorbing the UV radiation before it can damage the polymer, while light and colored mixtures contain instead UV absorbers that convert the UV radiation into heat. Additionally, special UV inhibitors are used to absorb the resulting radicals (HALS stabilizers). Ozone-protective agents (antiozonants) protect Molded Rubber before ozone cracking, mostly based on nitrogen compounds (p-phenylenediamine). They react with ozone more quickly at the surface than the rubber, but are usually only used in black blends because they discolor the surface. Additionally, paraffin and microcrystalline waxes added to the rubber mixture form a protective layer on the surface that is effective on statically loaded components; when subjected to dynamic deformation due to movement, they can tear apart.