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Whether or not a particular plastic product can be recycled depends a confluence of factors: the type of plastic, how it was manufactured, the collection infrastructure, and whether secondary markets exist for the material. 

recycling methods and challenges
contamination
downcycling
combining plastics of different resins


ALSO SEE:
recyclability: infrastructure
plastics recycling technologies
plastics science: polymers
about recycling plastics in nyc


Recycling Methods and Challenges

Recycling plastic involves physically and/or chemically breaking it down into a substance that can be used to make new products, usually in the form of pellets or flakes.

The most useful and valuable method is to break plastics down into its original polymer resin. The polymer resin is then used to make a new product of the same polymer resin. For example, a #1 PET water bottle could be recycled and made into another #1 PET bottle. Because of this, plastic products made entirely from a single pure polymer resin are some of the most easy to recycle.

Unfortunately, most plastic products are made from a mixture of polymer resin and additives such as plasticizers, lubricants, and pigments that create chemical and physical changes to the plastic (see plastics science: polymers).

In addition, different molding processes that plastics must undergo to become a product (for example, being blow-molded into a bottle versus extrusion-molded into a tray) can give the same polymer resin different chemical and physical characteristics.

Some additives and molding processes used in the creation of an original plastic product change the fundamental molecular structure of the polymer resin in ways that are difficult to reverse.

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Contamination by Different Resins or Residue

Plastic material can also be contaminated by foreign objects or residues that make their way into the materials being processed. Foreign objects can include plastic products of different polymer resin and/or molding types, food remnants, dirt, etc.

Contamination leads to a recycled material that is of lower quality than a pure polymer resin. That's because foreign substances can change the chemical make-up and behavior of the recycled material from what is expected. Levels of contamination can fluctuate, which further reduces the predictability and quality of the material being created.

Bioplastics (bio-based or biodegradable plastics) are considered contaminants in traditional plastics recycling programs. They are especially problematic since they closely resemble recyclable materials to the consumer who may place them in the recycling bin, but these plastics are not actually recyclable. Do not place bioplastic items in your recycling bin.

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Downcycling

Plastics that are chemically distinct (that are made up of different combinations of resinsadditives and molding processes) have unique characteristics, such as stiffness and melting point, and do not mix well in recycling processes. If recycled together, the resulting recycled material will likely not have uniform characteristics or predictable behaviors required by manufacturers of new products.

There continues to be advancement in techniques to recycle certain groups of plastics together, such as plastic film (bags) of differing resin types. The resulting recycled material is considered "degraded" or "downcycled" because it cannot be used for the same purpose as the original material.

Unfortunately, certain plastics, even if recycled only with the same type of material, cannot be broken down into a resin of the same quality of the original material. These plastics are also considered downcycled.

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Combining Plastics of Different Resins

Under very limited circumstances, different types of plastics can be combined to make a composite material without the heating, melting, or re-molding commonly used in most plastic recycling. The material that results is an aggregate of many small pieces of different types of plastic, held together with some kind of bonding agent.

This downcycled plastic aggregate material has very limited uses because it is neither strong nor aesthetically pleasing. It is used in some fencing and sound barrier applications. To date, firms producing this material find it hard to stay in business.

In NYC, to prepare and ship mixed plastics to the few firms that engage in mixed plastics recycling would be too expensive and unreliable to be worth the effort. For more info, see recyclability: infrastructure.

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