Numbers in the Arrows

Let’s call this blog a plastics primer.

Plastic Identification CodesThere are five groups of plastic polymers that are used worldwide in packaging. Each of those polymers has specific properties and its Plastic Identification Code (PIC) can identify each of them. That’s the number you find inside the three-chasing-arrow recycling symbol. That symbol indicates whether or not the plastic can be recycled into a new product. It used to be called the Resin Identification Code — introduced by the Society of the Plastic Industry in 1988 to provide a uniform system to identify types of polymers and help recycling companies.

Before recycling, most plastics are sorted according to their resin type. That sorting used to be done by hand, which is why those RIC numbers were so handy. Today, automatic sorting systems, which use near infrared scanners, are used to separate the plastic. Some plastic products are also sorted by color before being recycled, and the number is now called the Plastic Identification Code.
Once the plastics are sorted, the items are shredded. Those shredded fragments undergo a number of different processes to eliminate impurities, such as paper labels. Those processes also get rid of food waste, which can be absorbed by the plastic packaging. This material is melted and turned into various forms of pellets, which are then used to manufacture other products.

So, since you now know what those numbers are, here’s a guide to what they mean.

  • PET-1 is polyethylene terephthalate. Known for its clarity, strength and resistance to moisture, you’ll find it used in soft drink, water and salad dressing bottles; peanut butter and jam jars; and small consumer electronics.

  • PET-2 is high-density polyethylene. It’s known for stiffness, strength, toughness, resistance to moisture and permeability to gas. You’ll find it in milk, juice and water bottles; grocery bags; and some shampoo/toiletry bottles.

  • PET-3 is polyvinyl chloride. PVC is versatile and strong, and found in blister packaging for non-food items, electrical cable insulation, and rigid piping.

  • PET-4 is low-density polyethylene. It’s easily processed, strong, flexible and a barrier to moisture. Those reasons make it work for frozen food bags and squeezable bottles, such as ketchup bottles and clingy film wraps.

  • PET-5 is polypropylene. It’s strong and tough, boasting resistance to heat and chemicals including grease and oil. It’s also versatile and is a barrier to moisture. No surprise that it’s used in reusable microwaveable containers; kitchenware; yogurt containers; margarine tubs; microwaveable disposable take-away containers; and disposable item such as cups and plates.

  • PET-6  is polystyrene. It’s versatile and easily formed, which is why you will find it in egg cartons; packing peanuts; disposable cups, plates, trays and utensils.

  • PET-7 is a mix of various types of polymers. For that reason, there are no common properties because those depend on what polymers are added.  But it’s a sign of just how plastic-filled modern society has become.  You’ll find a combination of polymers in everything from cases for cell phones to sunglasses and automotive parts to protective shields.

— Frank Graff

Frank Graff is a producer/reporter with UNC-TV, focusing on North Carolina Science Now, a weekly science series that airs Wednesdays, beginning in August 2013, as part of North Carolina Now on UNC-TV. In addition to producing these special segments, Frank will provide additional information related to his stories through this North Carolina Science Now Reporter's Blog!

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