(Real Simple) -- This primer reminds you of what you can and can't recycle -- and why.
Food particles on paper can contaminate an entire batch of recyclables.
Plastic
Most plastics are recyclable," says Keith Christman, senior director of packaging at the American Chemistry Council Plastics Division, in Arlington, Virginia.
The problem is, not all plastics are recyclable everywhere.
Almost all recycling programs accept plastics numbered 1 and 2. (Look for the number on the underside of a product, inside the ubiquitous triangle of chasing arrows.)
But the numbers are not regulated federally; 39 states have various rules, so what you see can be inconsistent.
"The plastics industry has put the recycle symbol on everything," says Marti Matsch of Eco-Cycle, in Boulder, Colorado. "People think the symbol means the item is recyclable, but that's not always true." More than a tool for recycling, "the symbol identifies what a certain plastic is made of," Christman says.
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Here, a cheat sheet.
No. 1: Polyethylene terephthalate (PET, PETE), the most widely recycled plastic, is used for soft-drink bottles and is also commonly found in textiles, which explains why a bottle can be turned into fleece.
No. 2: High-density polyethylene (HDPE) is used for detergent bottles and grocery bags.
No. 3: Polyvinyl chloride (PVC or vinyl) is what salad-bar containers are made from.
No. 4: Low-density polyethylene (LDPE) is used for dry-cleaning and fresh-produce bags.
No. 5: Polypropylene (PP) is what makes bottle caps, yogurt cups, and drinking straws.
No. 6: Polystyrene (PS) is also known as Styrofoam.
No. 7: These "other" plastics, such as polycarbonate baby bottles, are generally not recyclable at most centers.
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Paper
Putting the wrong type in the wrong bin can make a difference.
Recycling facilities work to keep similar papers together so they can get the most money for their products. (For example, office paper, which has long fibers, is worth a lot more than the "mixed paper" of cereal boxes, which has shorter fibers.)
Another factor is food contamination. Plastic, glass, and metal containers are cleaned to remove food, but paper is not. Food particles can contaminate an entire batch, as the food (along with the paper) begins to biodegrade if it is left to sit.
When paper is recycled, it is pureed into a pulp "smoothie" and passes through screens that take out anything that's not paper: chunks of wood, plastic, or glass; paper clips; staples.
It's then treated with chemicals to remove inks, which means recycled office paper can still be white.
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Metal
Recycling metal saves an enormous amount of energy and money.
All steel products, for example, contain at least 25 percent steel scrap, which requires 75 percent less energy to produce than "virgin" steel and explains why scrap metal has become a valuable commodity.
As for aluminum cans, recycling just one saves enough energy to run your TV for 2½ hours.
Metal is separated into two piles -- ferrous (containing iron) and nonferrous. The device that figures this out? An industrial-size magnet that attracts ferrous metals, like steel, but not aluminum, which is nonferrous.
Glass
Recyclable glass almost always refers to "container" glass -- that is, bottles and jars. Other types, like windshields and Pyrex, have different melting points and are not accepted by most recyclers.
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All About Waste and Recycling • Environmental Policy • Boulder (Colorado)
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