Plastic Bottle Making Process
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The Popularity of Plastic Bottles
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Plastic bottles hold just about any type of liquid nowadays---soda, ketchup, shampoo. You'll find them in all shapes and sizes, too. For manufacturers, plastic bottles are inexpensive, lightweight and sturdy. What makes a plastic container considered to be a bottle is that the body shrinks down to a narrower neck before going out the opening.
What is PET?
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The most-common plastic bottle you see nowadays is the soda bottle. It is made from polyethylene terephthalate, also known as PET. PET is used for 14 percent of all plastic containers and 43 percent of soda bottles. It was developed in 1941, but it wasn't used for soda bottles until the 1970s.
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Before the Bottle is Made
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Before a plastic bottle can be manufactured, the PET must be made. PET is a polymer that is made from petroleum hydrocarbons. It comes from a reaction between terephthalic acide and ethylene glycol. The process to make PET is called polymerization.
Making the Bottle
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The process to make PET bottles is called stretch blow molding. PET pellets are injection-molded in a thin-walled plastic tube. The tube is then cooled and cut into shorter lengths. Each length of tube is inserted into a mold that is shaped like the bottle the manufacturer wants to create. A steel rod is inserted into the tube and blows out highly pressurized air. This pushes the plastic and PET against the inner sides of the mold. Under this high pressure and high temperature, the molecules in the PET polarize, in essence, crystallize, which give the bottle its strength. The consistent pressure also ensures a uniform thickness to the PET. The bottle bottom is made from a separate mold during the process and attached later.
Finishing the Bottle
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The mold is then cooled quickly to keep any of the PET from flowing inside the mold. The bottle is then removed from the mold and trimmed to remove and PET that leaked through cracks in the mold. The bottles are then packaged and sent to the company that ordered them. Lids and labels are made in an entirely separate process.
Recycling
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With the rapid acceptance of PET bottles in the marketplace, PET began to fill up landfills, which creates environmental problems. PET can be and is recyclable. The plastic can be remelted and mixed with unused PET to create new bottles.
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References
- Photo Credit Plastic bottles make up 43% of soda bottles. Courtesy of Wikimedia Commons.
