Plastic is a versatile product: it can be flexible or rigid, transparent or opaque. It can look like leather, wood, or silk. It can be made into toys or heart valves. Altogether there are more than 10 000 different kinds of plastics. The basic raw materials for plastic are petroleum and/or natural gas.
These fossil fuels are sometimes combined with other elements, such as oxygen or chlorine, to make different types of plastic.
Plastic recycling is the process of recovering scrap or waste plastics and reprocessing the material into useful products. For instance, this could mean melting down polyester soft drink bottles then spinning the polymer into fibres.Before recycling, plastics are sorted according to their resin identification code. PET, for instance, has a resin code of 1.
Many such problems can be solved by using a more elaborate monomer recycling process, in which a condensation polymer essentially undergoes the inverse of the polymerization reaction used to manufacture it. This yields the same mix of chemicals that formed the original polymer, which can be purified and used to synthesize new polymer chains of the same type. Du Pont opened a pilot plant of this type in Cape Fear to recycle PET by a process of methanolysis, but closed the plant due to economic pressures.
Another potential option is the conversion of assorted polymers into petroleum by a much less precise thermal depolymerization process. Such a process would be able to accept almost any polymer or mix of polymers, including thermoset materials such as vulcanized rubber tires and the biopolymers in feathers and other agricultural waste. Like natural petroleum, the chemicals produced can be made into fuels as well as polymers. A pilot plant of this type exists in Carthage, Missouri, using turkey waste as a feedstock. See the main article on thermal depolymerization. Gasification is a similar process, but is not technically recycling since polymers are not likely to become the result.
Recently, a process has also been developed in which many kinds of plastic can be used as a carbon source in the recycling of scrap steel.
Yet another process that is gaining ground with startup companies (especially in Australia, United States and Japan) is Heat Compression. The heat compression process takes all unsorted, cleaned plastic in all forms, from soft plastic bags to hard industrial waste, and mixes the load in tumblers (large rotating drums resembling giant clothes dryers). The process generates heat from the friction of the plastic materials rubbing against each other inside the drum, eventually melting all, or most of the material. The materials are then pumped out of the drum through heated pipes into casting moulds. The most obvious benefit to this method is the fact that all plastic is recyclable, not just matching forms. But criticism rises from the energy costs of rotating the drums, and heating the post-melt pipes.
The most-often recycled plastic, HDPE or number 2, is recycled into plastic lumber, tables, benches, truck cargo liners, trash receptacles, stationery (e.g rulers) and other durable plastic products and is usually in demand. The white plastic "peanuts" used as packing material are often accepted by shipping stores for reuse.
In Israel successful trials have shown that plastic films recovered from mixed municipal waste streams can be recycled into useful products.
Similarly, agricultural plastics such as mulch film, drip tape and silage bags are being diverted from the waste stream and successfully recycled into bulk resin commodities in Labelle, FL. Historically, these agricultural plastics have primarily been either landfilled or burned on-site in the fields of individual farms.
The environmental benefits of recycling plastic are that it produces less sulphur dioxide, less waste and less carbon dioxide.