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Plastics - From Recycling Bin to New Product

Where do recyclable plastics go?

By Roberta C. Barbalace

You've snatched a misplaced plastic milk bottle and root beer bottle from the trash. Before you plop them in the recycle bin, you flip each over to see what number appears in the triangle on the bottom. Sure enough, there is a "2" on the bottom of the milk container and a "1" on the root beer bottle. You may not be sure what each of those numbers stand for, but in most cases know that they must be tossed in different containers.

About 10 states have "bottle bills" requiring that a deposit be paid on carbonated beverage and sometimes other drink containers ^(1,6). As a result, the root beer bottles will need to either be returned to the store or to a privately owned redemption center for deposit refund. The milk bottle will either be tossed into a mixed plastic container, a plastic "2" bin, or simply into a mixed recycle bin. When recyclable materials are separated from other trash and sent to a Materials Recycle Facility (MRF) that receives only recyclables, the MRF is referred to as a "clean MRF." In some instances the recyclable material is commingled with other trash and arrives at the Materials Recycle Facility (MRF) dripping with spaghetti sauce, some moldy yogurt, and a copious quantity of bacon drippings. The recyclables are removed at the materials recycling center. This type of facility is commonly referred to as a "dirty MRF" ^{(1, 2)}.

Whatever route your plastic container takes, hopefully it will eventually make its way to a plastic recycling facility. The big question is still, "What eventually happens to my plastic container?" That depends on many factors. "Things like what?"-you might ask. You can probably figure out what the first factor is - the market. Remember that recyclables are basically a commodity. People in the plastic recycle market get price lists every day, so they know what price is being paid for all sorts of plastic according to plastic type and degree of pre-processing. If the market for a given type of plastic is high enough to at least break even, it may be sold and eventually be recycled. If it costs more to separate and transport the plastic well it might go into a landfill or incinerator or it could be kept at the transfer facility until the price is right. Remember that "recyclable" is not the same as "recycled ⁽²⁾." Some municipalities and/or states have very stringent recycle programs that will take a loss rather than send recyclables to a landfill or incinerator. Other municipalities recycle according to the current market prices. If the market price of a recyclable material is too low to bring a profit, the material may either be stored until the price rises, or sent to a landfill or incinerator with the non-recyclable municipal waste.

If a plastic makes it into the recycling loop, it will go through many processes before it emerges as a recycled product. Plastics are picked up and sent either to a Materials Recycle Facility (MRF), Intermediate Processing Facility (IMP), or Plastic Recycling Facility (PRF). Commingled recyclables or unsorted waste typically go to a MRF first. The plastics are separated from other waste and sent to a PRF. The plastic may be shipped to a PRF either baled or loose. If plastics have not been presorted into specific types of plastic, the sorting will have to be done before processing can begin. Note that segregated plastics, especially in the flaked for sale sell for a considerably higher price than unsorted plastics. Communities that can convince home-owners to separate their plastics for curbside pick-up or delivery to a drop-off center can send plastics directly to a PRF for a considerably higher price, than if the plastics were not presorted.

Plastics ending up at the PRF may need further processing before they can be "remanufactured." For instance, PET plastic bottles may need to be stripped of caps, labels and "plastic cups" that may be on the bottom of beverage containers ⁽⁶⁾. Finally, each type of plastic is ground into "dirty flakes." These dirty regrinds are sent to reclaimers.

At the PRF each type of plastic will then go through a specific process to prepare the recycle material for the "converters." The converter will process the plastic to "consumer grade" plastic that can be used by the end-user to make new products.

From this point forward each type of plastic will undergo different processes. The following is an explanation of how PET is prepared for remanufacturing.

The first purification process takes advantage of the fact that PET is heavier than water, and HDPE (the plastic from which the caps and bottom cups are made) are less dense than water. A float/sink classifier uses this difference in the physical properties of PET and HDPE to remove the HDPE from the PET. Simply pass the flakes through water. The PET sinks and the HDPE floats. The HDPE can be removed from the top of the water leaving the PET on the bottom. Some processors use a "hydrocyclone" to remove the HDPE ⁽⁴⁾.

The remaining PET flakes are dried and passed through magnetic field to remove stray aluminum from the PET. They may go through x-ray to remove PVC or even optical sorting devices. The degree of purification required will be dependant upon the end-use.

The result of all of this purification is a product known as a "clean flake." The clean flake can be sent to the end-user, or the reclaimer can transform the clean flakes into pellets.

The flakes or pellets are now ready to be sold to the end-user ⁽⁶⁾. There are many possible uses for PET that started as an empty carbonated beverage container. It can undergo a process called Injection Blow Molding and be converted into an agrochemical container, bathroom and toiletry products, or another carbonated beverage container ⁽⁴⁾. Extrusion Blow Molding is used to make bottles, containers, automotive fuel tanks, venting ducts, watering cans, boat fenders, etc. Thermoforming may be used to convert that coke bottle into hard formed objects such as laundry scoops ⁽⁵⁾.

This discussion has concentrated on the recycling process of PET. While there are differences in the recycling path for each type of plastic, the general procedure is similar to that of PET from the moment it is discarded until it is recycled to begin again as another plastic object. Presently, most plastic is derived from fossil fuels; however, bio-fuels are now being used in the manufacture of plastics. More importantly, plastics can be recycled many times. It is widely reported that plastics cannot be recycled indefinitely. However, the Environmental Plastics and Industry Council of Canada reports that "PET can be used indefinitely, because the recycled plastic has the same properties as the virgin material and doesn't disintegrate with time ⁽⁸⁾."

Plastic may not be the perfect material for all uses. Questions have been raised about possible toxins released when they are used in a microwave. Recent consumers were warned against freezing filled plastic drink bottles because of possible leaching of the plastics into the water. Since plastics do not degrade in landfills, they are hazardous to the environment. However, it would seem that if plastics were derived wholly from bio-fuel, used for appropriate purposes and recycled rather than disposed of, many of the environmental issues associated with plastics could be eliminated.

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Bibliography

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7. Recycling Today, Science and Technology Encyclopedia, McGraw Hill, 2005. http://www.answers.com/topic/recycling-technology (Accessed 1/27/07)
8. Plastic Bottles - Energy Consumption; Environmental Plastics Council http://www.cpia.ca/files/files/files_bottles.pdf (Accessed 1/27/07)

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Roberta Barbalace. Plastics - From Recycling Bin to New Product. EnvironmentalChemistry.com. Feb. 6, 2007. Accessed on-line: 12/21/2024
https://EnvironmentalChemistry.com/yogi/environmental/200702plasticrecycling.html
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