Dear EarthTalk: Why can't plastics of all types, instead of being initially sorted, simply be melted together to be separated later?

Author:Schand, L.
 
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Dear EarthTalk: Why can't plastics of all types, instead of being initially sorted, simply be melted together to be separated later? It must be a monumental and error-prone task to separate truckloads of plastics.--L. Schand, via e-mail

The reason plastics aren't typically melted together and then separated later is a matter of both physics and economics. When any of the seven common types of plastic resins are melted together, they tend to separate and then set in layers. The resulting blended plastic is structurally weak and difficult to manipulate. While the layered plastic could in theory be melted again and separated into its constituent resins, the energy inputs required to do so would make such a process cost prohibitive.

As a result, recycling facilities sort their plastics first and then melt them down only with other items made of the same type of resin. While this process is labor-intensive, the recycling numbers on the bottom of many plastic items make for quicker sorting. Many recycling operations are not only reducing sizable amounts of waste from going into landfills but are also profitable if managed correctly.

Manufacturers of plastic items choose specific resins for different applications. Recycling like items together means the reclaimed polymer can be used to create new items just like their virgin plastic forebears. The seven common types of plastic are: #1 Polyethylene terephthalate (PET or PETE); #2 High-density polyethylene (HDPE); #3 Polyvinyl chloride (PVC); #4 Low-density polyethylene (LDPE); #5 Polypropylene (PP); #6 Polystyrene (PS); and #7 Other/Mixed (O). One complicating factor is trying to recycle unmarked plastics and those embossed with a #7 (representing mixed resins, also known as polycarbonate). According to Earth911, a leading online source for finding recyclers for specific types of...

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