Biodegradation of Polymers in Marine Environment - Polymers in a Marine Environment - page 84

3.3.2.3 Photo-degradation
A photo-initiated oxidation process is called photo-degradation, which results in the
absorption of UV radiation and the generation of free radicals. A chromophoric group
must be present to absorb energy. The reaction occurs on the surface layer. Most of
the time ketone groups are formed on the polymer chain, either by thermolysis or
photolysisofhydroperoxide.ThisprocessoccursbyNorishtypeIorNorishtype
II reactions. The initiators of photo-degradation include transition metals, ketones,
quinones or peroxides.
Polymeric materials that are exposed to the marine environment foul which in turn
modiies the surface, turning it opaque and limits the penetration of light through
the material [27]. This slows down the process of photo-degradation.
Figure 3.3 Advanced stage of biofouling on PET (polyester)
Biofouling adds more weight to the material and weighs it down ( Figure 3.3 ).
The material then gets submerged which further slows down the rate of photo-
degradation because the UV light in sunlight is unable to penetrate through seawater.