UV resistant plastic is critical for many outdoor applications and those exposed to the sun or UV radiation from another source. If you’ve seen plastic items discolor or turn yellow or chalky after prolonged exposure to the sun, you have seen the impact of harmful ultraviolet (UV) rays. While it may appear cosmetic, UV can cause some plastic materials to break down through photo-oxidative degradation.
Harmful Impact of UV Radiation
UV radiation consists of high-energy photons that are invisible to the human eye. UV falls between 400 nm and 10 nm on the electromagnetic spectrum. For comparison, the human eye can detect wavelengths between 400 nm to about 780 nm on the electromagnetic spectrum.
Photo-oxidative degradation occurs as UV energy interacts with polymers’ molecules. The photons become excited and can break the bonds of the polymer’s backbone chain, reducing its molecular weight. This process forms free radicals, which are reactive unpaired electrons. These naturally want to be paired, so they will pair with other atoms, which can create unpredictable and damaging reactions. Chromophores are the atom groups responsible for a compound’s color. When UV degrades it, The free radicals created begin to wreak havoc on the polymer’s molecular structure.
The damage caused by a specific UV wavelength depends on the bonds present in the plastic and the intensity and length of exposure. For example, the maximum degradation for polyethylene (PE) is around 300 nm, and for polypropylene (PP), it is about 370 nm. These broken bonds result in reduced molecular weight, mechanical properties deterioration, and a discolored, chalky, brittle polymer.
Varying Degrees of UV-Resistant Plastic
The interaction between UV radiation and polymer varies by material and chemical structure. Some plastics are more naturally resistant to UV degradation, while others are unacceptable. Plastics that in an unmodified form are most susceptible to UV degradation include polyoxymethylene (POM), polycarbonate (PC), Acrylonitrile butadiene styrene (ABS), and polyamide 66 (nylon 66). Others only have a fair resistance, which may not be sufficient for harsh environments and long-term exposure. Some plastics with a fluorine bond, such as PTFE, are more resistant to bond breakage from UV rays.
Using Stabilizers to Create UV-Resistant Plastics
To protect susceptible plastics from damage, manufacturers add UV stabilizers at very low levels, which are either combined with the base polymer during manufacturing or added to the masterbatch. The additives are either UV absorbers, quenchers, or hindered amine light stabilizers (HALS).
As the name suggests, UV stabilizers absorb UV radiation to prevent photo-oxidation reactions and transform it into heat that is harmlessly dissipated. UV absorbers, such as carbon black, are a low-cost method for stabilizing plastic but may not be effective long-term for all products.
Quenchers interrupt the photo-oxidation reaction by quenching the energy produced by the reaction and returning the excited molecules to a ground state so that they can perform their intended function within the molecule.
HALS trap the free radicals that are formed so that they can’t do damage. For long-term use, HALS are the better choice.
EnCom UV Enhanced Polymer Solutions
For all your outdoor and UV-exposed challenges, EnCom Polymers can provide a UV resistant plastic solution that will fit your unique needs. We can create a masterbatch polymer with UV-resistant or UV-stabilized enhancements. We have standard grades of commonly used polymers that offer UV protection, or we can customize a polymer to solve your specific challenge. Contact us with your requirements and get the custom formulation that meets your product, processing, and production goals.
For More Information
Please call our main office at (866) 481-7700 and ask to speak to a technical specialist.