Chemistry
Mechanisms of Photodegradation of Polymers Under Ultraviolet Exposure
Quick fact
UV radiation, particularly in the 300–400 nm range, can directly break carbon-carbon bonds in many polymers, but the more damaging process often involves oxygen: photooxidation, which creates radicals that trigger chain reactions, leading to loss of strength, yellowing, and embrittlement.
Why this is interesting
You've seen plastic chairs left outside become brittle and crack after years of sun. What is happening inside the material that makes it fail so dramatically?