Polypropylene (PP) is a thermoplastic polymer, a material that can be melted and reformed multiple times without significant degradation. It is a rugged and versatile material, belonging to the group of polyolefins, which are polymers made from simple olefins (alkenes) as monomers. Its chemical formula is (C₃H₆)_n. PP is produced via chain-growth polymerisation from the monomer propylene. It is renowned for its excellent chemical resistance, high fatigue strength, good insulation properties, and relatively low cost, making it a popular choice across various industries. From packaging and automotive components to textiles and medical devices, PP's unique balance of properties makes it indispensable.

Recycling polypropylene is a multi-step process. Firstly, PP waste is collected and sorted, often identified by the recycling symbol #5. Contamination is a significant challenge, so thorough cleaning is essential to remove food residues, labels, and other materials. Once cleaned, the plastic is shredded into flakes, which are then washed again. These flakes are then melted down and extruded into pellets. These pellets, known as "regrind," can be used to manufacture new products, reducing the demand for virgin plastic. Advances in chemical recycling are also emerging, breaking down PP polymers into their basic monomers, which can then be repolymerised into new, high-quality plastic. Understanding this process highlights the importance of proper waste segregation at home.