It is necessary to see the chemistry between plastics and the environment in ambient conditions. The plastics deteriorate because of this interaction, and often their exterior characteristics change occurring in the creation of new functional molecules. It is a dynamic situation with continuous varying parameters – Polyethylene (PE), Polypropylene(PP), and Polyethylene Terephthalate (PET) deteriorate through the mechanisms of the photo, thermal, and biodegradation. The three polymers degrade with different speeds and different ways. Under natural conditions, photo- and thermal degradation are alike.
For polyethylene (PP), photo-degradation results in absolute peaks which shows ketones, esters, acids, etc. on their infrared spectrum.
The same is for polypropylene (PP) but this polymer is more opposing to photo-degradation.
The photo-oxidation of PET requires the creation of a hydroperoxide molecule involving the formation of photoproducts in several ways.
These three polymers, influence with microbes and generation of bioplastics are different. Generally, biodegradation occurs in a decrease of carbonyl contents if the sample has already been photo-degraded by exposure to UV.
Studies say that the degradation of plastics is very subjective to the regional environmental conditions that are usually a mixture of those simulated in laboratory conditions. For example, investigations suggested that fragmentation of plastic by solar emission can happen within years on the seashores, whereas PET bottles stay intact over 15 years on sea bottoms.
Photodegradable polymers were synthesized to have them destroyed after use (e.g., in a landfill). Another approach was the incorporation of suitable groups (e.g., carbonyl) in the polymer backbone to make polymer photodegradable by sunlight or UV. A problem arises because light exposure conditions on a landfill cannot be regulated.
Biodegradation is the degradation created by the biological activity, mainly by enzymatic action, driving to a vital change in the chemical structure of the exposed plastic and resulting in the production of carbon dioxide, water, mineral salts (mineralization) and new microbial cellular constituents