The main elements in plastic include carbon, oxygen, hydrogen and chlorine. Some plastics may also contain sulfur, depending on how they are made.
Plastics are typically carbon based. Carbon atoms are connected to other elements and when the connection of other elements with carbon results in long chains, the plastic is a thermoplastic. Any plastic that can be melted is a thermoplastic.
Often, additives are put into a plastic mixture. These additives may include lubricants, antimicrobials, antioxidants or flame retardants. These additives give the plastic a specific property and can protect the plastic from water or heat damage and make it resistant to bacteria.