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Plastic recycling is the process of recovering scrap or waste plastics and reprocessing the material into useful products, sometimes completely different in form from their original state. For instance, this could mean melting down soft drink bottles then casting them as plastic chairs and tables.

Before recycling, plastics are sorted according to their resin identification code, a method of categorization of polymer types, that was developed by the Society of Plastics Engineers in 1988. Polyethylene terephthalate, commonly referred to as PET, for instance, has a resin code of 1.

1 Processing
2 Applications

Processing

When compared to other materials like glass and metal materials, plastic polymers require greater processing to be recycled.[citation needed] Plastics have a low entropy of mixing, which is due to the high molecular weight of their large polymer chains. A macromolecule interacts with its environment along its entire length, so its enthalpy of mixing is large compared to that of an organic molecule with a similar structure. Heating alone is not enough to dissolve such a large molecule; because of this, plastics must often be of nearly identical composition in order to mix efficiently.

When different types of plastics are melted together they tend to phase-separate, like oil and water, and set in these layers. The phase boundaries cause structural weakness in the resulting material, meaning that polymer blends are only useful in limited applications.

Another barrier to recycling is the widespread use of dyes, fillers, and other additives in plastics. The polymer is generally too viscous to economically remove fillers, and would be damaged by many of the processes that could cheaply remove the added dyes. Additives are less widely used in beverage containers and plastic bags, allowing them to be recycled more frequently.

The use of biodegradable plastics is increasing. If some of these get mixed in the other plastics for recycling, the recycled plastic is less valuable.

Applications

Post-consumer PET (number 1) is often sorted into different color fractions. This sorted post-consumer PET waste is crushed, pressed into bales and offered for sale to recycling companies. PET flakes are used as the raw material for a range of products that would otherwise be made of polyester.

PVC- or Vinyl Recycling has historically been difficult to perfect on the industrial scale.[citation needed] But within the last decade several viable methods for recycling or upcycling PVC plastic have been developed.

The most-often recycled plastic, HDPE or number 2, is downcycled into plastic lumber, tables, roadside curbs, benches, truck cargo liners, trash receptacles, stationery (e.g rulers) and other durable plastic products and is usually in demand.

The white plastic foam 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 household products such as buckets.

Similarly, agricultural plastics such as mulch film, drip tape and silage bags are being diverted from the waste stream and successfully recycled into much larger products for industrial applications such as plastic composite railroad ties. Historically, these agricultural plastics have primarily been either landfilled or burned on-site in the fields of individual farms.