How Is a Plastic Bottle Made?
- Though synthetic replacements for natural materials such as wood, rubber, or glass have been attempted, and created, since the early 19th century, it wasn't until 1909 that Belgian-born American inventor Leo Hendrik Baekeland invented what scientists consider the first true plastic. His invention, which he called "Bakelite," was a combination of formaldehyde and carbolic acid which was used for everything from telephone parts, to costume jewelry, to electrical insulation.
True plastics are a relatively stiff material made of "polymers." Polymers are long chains of molecules made by joining smaller molecules together. By mixing formaldehyde and carbolic acid, Baekeland created a relatively sophisticated plastic that was easily molded and set into a rigid form. - There are two basic methods to making a plastic bottle. The first is something called "thermomolding," which heats the plastic sheets until they are soft and pliable. Then the sheets are formed around a shape using more heat and a pressurized mold. After releasing from the mold, the bottle cools very quickly and is ready to be filled.
The other method is called "blow molding" and works on the same principle as blowing up a balloon. First, a sheet of plastic is formed into a tube. The tube is placed inside the mold and injected with hot gas. The hot gas causes the tube to expand to take on the shape of the mold. Once the bottle is formed, the mold releases the bottle, which cools quickly and is ready for use.
In both methods, the screws on the neck of the bottle are formed as part of this process, because it is the most efficient way to acquire a uniform screw shape. - Plastic was adopted as a replacement for glass in the making of bottles. Plastic is a mere fraction of the weight than glass, it is relatively cheap compared to glass, and is almost as recyclable as glass. Plastic also transfers cold and heat better; this means that a plastic bottle will allow the liquid inside to become colder, faster. The trade-off, however, is that glass bottles are keep beverages colder longer than plastic.
Plastic bottles had a huge impact upon the beverage industry. For instance, milk was often sold in quart or half-gallon glass bottles because anything larger was heavy and cumbersome to use or carry. In the late 1960's, dairies began switching to plastic half gallon and the new, larger gallon jugs. This allowed dairy producers to sell through supermarkets and stores instead of relying upon milk delivery services. Also, unlike glass bottles which had to be returned, washed, and sanitized, plastic offered a disposable method of milk delivery which cut down on overhead for dairy producers. - Originally, plastic was envisioned as a cheap, disposable alternative to heavy, expensive glass. What was not known at the time was the environmental effects of disposing of plastics in landfills and other traditional waste disposal methods. Plastic can take up to 450 years, or more, to "break down" into its components. In recognition of the immense problem that plastic poses to landfills and garbage disposal, many municipalities and states offer some form of recycling. For example, California, Michigan, and Maine all require deposits on plastic and other beverage containers, which is then refunded to the consumer when they recycle those items. In cities such as New York City, Montreal, and even Cincinnati, Ohio, municipal regulations require that the waste management companies provide recycling bins and curb-side pick-up of recyclable materials such as plastic bottles. Other municipalities and states, however, do not require recycling from the consumer nor the waste management company.
- Consumers may note that plastic bottles, much like almost anything else made of plastic, comes in different thicknesses, rigidity, and opacity or color. Sometimes the difference is merely due to how much plastic is used in making the item, but usually it is due to the different resins used to make plastic. Typically, there is a small three-arrow triangle on the bottom of a plastic bottle with a number between 1 and 7 inside and a three or four-letter combination under the triangle. These are used by the recycling center to sort the different plastics into their appropriate resins for better recycling.
The most commonly used plastic in making plastic bottles is resin #1 Polyethelene Terephthalate or PET. PET bottles are typically clear and stiff, resisting leaks well. Upon recycling, PET is ground up into small flakes and then spun into the fiber called "polyester" which is used to make carpet, "fleece" clothing, and food containers.
The second resin used in making plastic bottles is resin #2 High Density Polyehtelene or HDPE. HDPE bottles are used to hold milk, juice, and water, are typically clear or milky white, and somewhat rigid and resist leaks very well. HDPE has a good resistance to chemicals and so is often turned into synthetic decks, picnic tables, and fences (as well as bleach or other chemical containers) upon recycling. In these forms, it is able to resist the weather much better than conventional wood sources.