Degradation of Plastics and Formation of Primary and Secondary Microplastics

Plastic waste is inevitably introduced into the environment, and its exposure results in the deterioration of mechanical and physicochemical properties, leading to the formation of plastic fragments. These fragments are classified as microplastics (MPs) when their size is less than 5 mm. The predominant plastic particles categorized as MPs that are discharged into the environment consist of polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and polyethylene terephthalate (PET). This chapter presents an analysis of the various degradation processes, including photo, thermal, mechanical, chemical, and biodegradation, through which different types of plastics convert into MPs. Additionally, a comprehensive effort has been made to compile the primary mechanisms and characterization methods associated with plastic degradation, along with investigations into the environmental degradation of plastics, to enhance the understanding of the plastic degradation processes. Furthermore, the toxicity of products and byproducts generated during the processes has been highlighted.