*3.1.4 Photodegradation*

Photodegradation of plastic is mediated by sunlight UV radiations, both UVB (290–315 nm, high-energy radiation) and UVA (315–400 nm, medium-energy radiation) [12, 76]. Photodegradation of plastic involves free radical formation and oxidation of the plastic polymers, resulting in the formation of peroxides, which eventually breaks into alkoxy and hydroxyl radicals, similar to the thermal degradation mechanism. Photodegradation in the atmosphere results in the formation of free radicals to break different plastics depending on their chemical structures. For example, the presence of chromophores (alternating or conjugating carbon double bonds) in PP, PE, and PVC, phenyl rings in PS, and ethylene glycolate and terephthalate groups linked with ester bonds in PET mediate the free radical formation reactions as a result of photodegradation [12].
