The main compounds of plastic raw materials are highly polymerised composites made from carbon and hydrogen, derived from substances such as petroleum and natural gas. Crude gasoline made by refining crude oil is the primary product that is used for making plastics. About 4% of the global crude oil is used for plastic manufacturing.
Plastics can be categorised into two groups. This is based on the way they react when heat is applied to them – thermoplastics and thermosetting plastics.
Thermoplastics experience strong molecular motion, making them soften. As the temperature drops again, they become hard. This can be done repeatedly. This category includes, but is not limited to, PET, Low Density Polyethylene (LDPE), and Polyvinylchloride. (PVC), High Density Polyethylene (HDPE), Polypropylene (PP) and Polystyrene (PS).
Thermosetting plastics experience a mild molecular action but still soften. They form a dense 3D structure; therefore, once cooled, they cannot be successfully reheated and reused.
