Final answer:
The two main expanded plastics in use today are polystyrene (PS) and polyethylene (PE), used in a variety of products and identified by specific plastic identification codes.
Step-by-step explanation:
The two main expanded plastics in use today are probably polystyrene (PS) and polyethylene (PE). Polystyrene is widely used in items such as foam packing, insulation foam, and disposable cutlery. Polyethylene, the most common plastic, has a significant presence in products like plastic bags, bottles, and toys. Both PS and PE are derived from petrochemicals and are part of the larger family of synthetic organic solids known as plastics. These polymers are not readily biodegradable and are often recycled to minimize environmental damage and petrochemical consumption.
Each type of plastic polymer can be recognized by its plastic identification code (PIC), with low-density polyethylene (LDPE) being marked as "4". Polyethylene terephthalate (PET), commonly used for containers and clothing fibers, should not be confused with polyethylene in this context.