Plastic recycling is the process or recovering waste or scrap plastics and reprocessing the material into other, useful products, completely different from their original state at times. For example, plastic bottles once used for soft drinks are recycled and turned into a park bench. Recycling is met with mixed reviews. Some say that more energy and money are put into the recycling effort than what you’ll ever get out. And others say that recycling is a very effective way to stop pollution, conserve landfill space, and help our planet recover from excess carbon emissions. Regardless of opinions, plastic recycling continues to be big business, and many of the recycled items can be commonly found in millions of homes, parks, schoolyards, etc.

Plastic polymers require greater processing to be recycled than glass or metal materials. Plastics have very 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 quite large in comparison to that of an organic molecule with a similar structure. Heating the plastic alone is not enough to dissolve such a large molecule. And because of this, plastics must often be nearly identical in composition to mix efficiently.

When different types of plastic are melted together, they tend to undergo phase-separation, similar to oil and water, and set in these different layers. The phase boundaries cause structural weakness in the material, and the polymer blends are only useful in limited applications. Another barrier to recycling is the widespread use of dyes and fillers and other additives in plastics. The polymer is too viscous to efficiently remove fillers, and would be damaged by many of the processes that could cheaply remove added dyes.

The use of biodegradable plastics is increasing rapidly. If some of these get mixed in with other plastics during the recycling process, the final product becomes less valuable. Many of these problems can be solved using an elaborate monomer recycling process, in which a condensation polymer undergoes the inverse of the polymerization reaction used to manufacture it. This yields the exact same mix of chemicals that formed the original, which can be purified and used to synthesize new polymer chains of the same type.

Another potential option is the conversion of various polymers into petroleum by a much less precise thermal depolymerization process. This process would be able to accept almost any polymer or mix of polymers, including thermoset materials like vulcanized rubber tires, and biopolymers in feathers and other agricultural waste. Like natural petroleum, the chemicals produced can be made into various fuels and polymers. A pilot plant of this type exists in Missouri, using turkey waste as input material. A new process has recently been developed in which many kinds of plastic tubing can be used as a carbon source in the recycling of scrap steel.

Tags: how plastic is recycled, plastic recycling, recycling plastics

This entry was posted on Monday, September 29th, 2008 at 11:44 am and is filed under Business, Plastics, recycling. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.