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How does polystyrene recycling work?

        Science | Green Science

Polystyrene Recycling Methods

Polystyrene-hungry Bacteria

The polystyrene industry claims a recycling rate of about 12 percent, according to the Alliance for Foam Packaging Recycling, but that includes scraps from EPS manufacturing, which are immediately reused. The fact is that it's often easier and cheaper to produce new polystyrene than it is to collect, transport and process material for recycling.

The most direct way for consumers to recycle polystyrene is to reuse it. This method doesn't work as well with coffee cups and plastic forks, but it's ideal for packaging materials. Packing peanuts can simply be collected and used again. Shippers may take rigid packaging and chop into small pieces to use as loose packing. UPS accepts packing peanuts from the public for reuse.

Used polystyrene can also be reprocessed for use in creating other products. For example, the Dart Container Corporation, the largest producer of polystyrene food containers, has four plants in the U.S. and Canada that receive EPS from schools, supermarkets, hospitals and other users. Here's how the reprocessing works at their plants:

  1. The material to be recycled is shipped to the plant and inspected to remove contaminants like paper and food.
  2. Sorting separates clean material from soiled waste that will need washing.
  3. The waste is fed into a grinder where it is processed into "fluff." Any EPS that is not already clean is washed and dried.
  4. Heat and friction are used to melt the fluff, removing all the air.
  5. The melted material is pushed under pressure into a die with small openings and extruded as strands of polystyrene, which are cooled with water and chopped into pellets.
  6. The pellets are shipped to manufacturers to be used in everything from toys to sun visors to building insulation.

Carrying truckloads of light, bulky polystyrene to recycling centers is usually not economical. Recyclers have found ways to compact the material to a more manageable size. Balers take foam packaging and compress it, reducing the bulk somewhat. Another method is to use limonene, a natural solvent made from orange peels. Limonene dissolves and concentrates EPS and can itself be reused. The chemical causes the EPS foam to "melt" without heat, reducing it to 5 percent of its original size. Thermal compaction uses heat to reduce chopped EPS to a concentrated brick that's easier to ship.

When it is burned in municipal incinerators, polystyrene yields nothing but carbon dioxide and water vapor. It's a good fuel for waste-to-energy programs that capture the heat and turn it to useful purposes, a process known as thermal recycling.

The polystyrene industry has been working to make recycling the material easier for consumers. For example, the Plastic Loose Fill Council's Web site can direct you to a nearby business that accepts used EPS packaging. Or you can call their "Peanut Hotline" to learn where to take loose EPS. Drop-off centers can also be found through the Earth911 Web site. The Alliance of Foam Packaging Recyclers allows consumers to mail in non-food EPS for recycling.

If recycling polystyrene sounds like a lot of trouble, what's the point of doing it? Read on to find out some reasons why.


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