EXPANDED POLYSTYRENE & POLYSTYRENE PROCESSING


There are several techniques available to recycle expanded polystyrene (EPS) foam packaging and solid polystyrene waste into useable polystyrene. The technique varies with the source of the waste and the intended use of the recycled material.


POST-INDUSTRIAL FOAM WASTE

Waste from EPS foam packaging plants is usually shredded into small particles called regrind which is reused as filler material in the manufacture of EPS packaging parts. To make this filler, the foam material must be ground into small pieces and these pieces sifted to get the appropriate filler size for the product. At Verpola, in Belgium, the chunks are ground to bead size and the bead is sold for use in concrete and brick products.

 

 


CLEAN POST-CONSUMER FOAM WASTE

Clean post-consumer packaging waste is collected from assembly plants and product distribution centers such as computer stores. This waste is condensed (compacted) into a dense foam block at the collection center and shipped to a foam recycler. Compaction of the foam makes it easier and cheaper to handle and transport to a recycler. At the recycling plant, the compacted blocks are cut into small chunks of foamed plastic and then fed into an extruder where the material is heated, mixed and pelletized into solid (unfoamed) polystyrene beads or tubes. These beads or tubes can then be blended with other batches of polystyrene to obtain the desired material properties for a specific plastic product such as such as plastic lumber. They can also be mixed with a foaming agent or a gas in an extruder and formed into foamed parts such as packaging peanuts or tubes.

 

 


DIRTY EPS POST-CONSUMER FOAM WASTE

Dirty post-consumer EPS waste, collected from local garbage (dirty packaging foam, used foam plates) requires more complex processing than clean EPS. Before the foam can be reprocessed it must first be freed of food and other contaminants. A technique to sort the foam from these contaminants has been developed by Utah State University in conjunction with Larry McIntyre of The Recycling Professionals, Inc. In there approach, the foam is first shredded into large pieces so that it can be easily handled and moved on a conveyer system. Then, the chunks of contaminated foam are rinsed in water and floated in a water bath. The food and saturated paper sink to the bottom of the water bath while the foam chunks float. The floating foam is then moved into the cleaning systems were it is washed to remove grease and dirt from the plastic. The cleaned foam is then ground into smaller components and densified. Densification of these small chunks of foam is done using the HudnutŠ process that uses heat to shrink and compact the foam material. The compacted material is then fed to an extruder to make foam or solid polystyrene.

 


POST-INDUSTRIAL AND POST-CONSUMER SOLID POLYSTYRENE WASTE

Solid polystyrene waste like CD cases and plastic dinnerware are ground into solid chunks and fed into an extruder to form polystyrene beads or products. Before a batch of recycled polystyrene is used to make solid or foamed parts, it must be characterized to determine its properties such as melt index or impact strength. Then, this batch is blended with other batches of recycled and new polystyrene to obtain the desired properties for a new product.

At PRS in Belgium,aluminum laminated polystyrene waste (generated in the production of aluminum foil lids for the food industry) is converted into aluminum and polystyrene in a unique process that separates to the plastic from the metal.


PROCESSING CHALLENGES FOR RECYCLING EPS AND PS:

  1. It is very difficult to remove dirt and grease from EPS foam. Consequently much of foam in the trash ( foam plates and foam packaging) are not processed currently.

  2. Foamed material soaks up water when washed or stored in outside containers. This changes the density of the material and makes it more difficult to weigh, sort and handle.

  3. It is difficult for the consumer to distinguish EPS foam from polyethylene foam so this is often a contaminant in the EPS brought to the reprocessing center.

  4. Some EPS materials such as home insulation contain flame retardants. When these materials are mixed with foam from packaging and other waste that do not contain flame retardants it significantly changes the flow behavior and properties of the material. Flame retardant material is considered contaminants in current EPS recycling processes and can ruin an entire batch of material.

 

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