**5.5 Bio- and photo-degradation**

The biodegradation of PE is a process whereby microorganisms are used to modify and consume the polymer as a primary source of energy and, by so doing, change the physical and chemical properties leading to structural deterioration, weight loss, and eventual gas evolution. Polyethylene biodegrades naturally over a long period. It takes polyethylene films up to 300 years to biodegrade and polyethylene terephthalate more than 450 years to do the same too. Biodegradation of this polymer can be enhanced by introducing microbes, sunlight, moisture and increasing the hydrophilic properties through modification during production. The Physico-chemical method of PE degradation includes UV and thermal treatment, oxidation of PE with nitric acid followed by the microbial attack, and catalytic enzyme degradation. All these cause reductions of polymer chain size, modification of the structure of the polymer, and eventual weight loss.
