If you look at the bottom of most plastic bottles and many plastic products, you will see a number or numbers surrounded by arrows that form a triangle. These numbers were developed by the Society of the Plastics Industry or SPI, and they are part of a resin identification coding system and commonly known as resin codes. Basically, the purpose of the code is to identify the type of plastic that was used to create the plastic.
In many parts of the country, items with a number one or number two are the only types accepted for municipal recycling programs. The number one indicates items that are made from the polymer polyethylene terephthalate or PET which includes soft drink bottles and water bottles. Biaxially oriented PET film is known more commonly as Mylar, and this is used for thin, flexible food packaging and other products. Thermoforming is used to create these products, which begin, as a large sheet of thin plastic. Heat is applied, and the plastic is formed to a mold, then cooled and trimmed to create a finished product.
If you see a number two on your product, this is a resin code that identifies the polymer HDPE or high-density polyethylene. Everything from grocery bags to hula hoops to milk jugs is created with this HDPE plastic. Even plastic surgeons sometimes use this plastic as part of surgeries for facial reconstruction. Again, this type of plastic is one of the two most common types and one of the two most often accepted by recycling centers around the country, although you typically don’t pay a deposit nor can you turn in these items and get your deposit back, as you can with water bottles and soft drink bottles.
The number three is used as a resin code to identify products made from polyvinyl chloride, which is commonly known as PVC. PVC is often used to create pipes and used in construction, but this plastic also is used to make plastic bottles that hold cleaners or other non-edible products and even used to create many toys. LDPE or low-density polyethylene is identified using a number four, and this plastic is often used in science labs because it is not affected by liquids that are acids, alcohols or bases. In addition, every time you buy a six-pack of beer or soft drinks, those flexible plastic rings are made from LDPE.
While it might not seem like diapers and carpet have much in common, both contain a bit of resin number five, which is polypropylene. This is a durable polymer which is also used to make bottle tops, such as flip tops on ketchup or salad dressing, as well as furniture. Because it is fairly heat resistant it can be used in laboratories, as well. Polystyrene is yet another type of polymer, and it is marked with resin code six and is often known by the brand name of Styrofoam. But generic versions of this polymer are used to create a variety of containers and cups, as well as packing peanuts that keep items safe in parcels during transit.
Strangely, there is no number eight, but there is a seven and a nine. Seven contains items that were created from an assortment of plastics, as well as nylon products and acrylic products. Nine is called ABS or acrylonitrile butadiene styrene, and it is very hard and durable and used to make Legos as well as musical instruments, pipes, golf club heads and much more.
Lenna Stockwell loves blogging about how stuff is made. To get further information about retail product packaging or to find out more about food packaging design, please visit the Indepak.com website today.