PET - polyethylene terephthalate, is a clear, strong and lightweight plastic belonging to the polyester family. PET began to be used for packaging in the middle of the 1960’s. PET was introduced in the production of films used in photography, video cassettes, photographic plates for X-rays and in packaging. At the beginning of the 70’s. the method for the production of bottles by blowing with biaxial orientation was developed. In the early 1970’s, the technique for blowing bottles was developed commercially.
The list of advantages for PET bottles is long. Let’s start from the beginning:
How is it made?
Polyethylene Terephthalate (PET) is a linear thermoplastic, long-chain molecule consisting of repeating units. PET resin is made through polycondensation of terephthalic acid (PTA) and ethylene glycol (EG) at high temperature and high pressure and followed by solid state polymerization.
Depending on its thermal processing, PET may exist both as an amorphous (transparent) and as a semi-crystalline (opaque and white) material. The Intrinsic Viscosity (IV) is an important characteristic of PET. The IV of the material is measured in dl/g (deciliters/gram), and is dependent upon the length of its polymer chains – the molecular weight of the polymer.
There are several PET grades:
| 0.60 dl/g | Fiber |
| 0.65 dl/g | Film |
| 0.76-0.84dl/g | Bottles |
| > 0.85 dl/g | Tire cord and strapping tape |
What are the applications for PET resin?
PET is used to make beverage, food and other liquid containers, synthetic fibers, as well as for some other thermoforming applications. The food industry has almost completely replaced glass with plastic bottles, even for wine and beer.
How can PET be identified?
Consumers can identify PET containers by the #1 recycling code symbol found on the bottom.
How is a bottle made?
Manufacturing PET bottles requires combining ethylene glycol and terephthalic acid to produce PET resin in the form of small pellets that resemble rice. These pellets are then melted at a temperature of 250 - 300ºC. When a liquid state is achieved, the plastic mass is injected into a mold to produce a ‘preform’—a thick-walled test tube with a finished neck and set of cap threads. It crystallizes while cooling, which gives the preform its desired features. The preform is then heated to a temperature of about 80º C, which makes it flexible. After placing it in a suitable mould, it is inflated with a high-pressure stream of air until it reaches the desired bottle shape.
What are the advantages of PET?
PET plastic has become exceptionally popular in recent years. Consumers appreciate its practical features demonstrated in its strength, resistance to breaking and low weight. However, its other advantages are also important: aesthetic appearance, a wide range of formability and colouring options and high transparency. More importantly, PET can be very easily processed by almost all recycling methods applied to polymer materials.
Light Weight / low total package weight - in 1989, 500 ml water bottles were composed of 24 grams of PET resin. Today, less than 10 grams of PET are used in 500 ml water bottles.
Safe / Unbreakable / Inert - PET is a very inert material that is resistant to attack by micro-organisms, and does not react with food products, which is why it is widely preferred for packaging foods, beverages and pharmaceuticals. Health-safety agencies around the world have approved PET as safe for use with foods and beverages.
Sustainability / much-reduced transport energy - Although the basic materials used for PET are petroleum based, the environmental impact of PET is very favorable in comparison to glass, aluminum and other recyclable container materials. That's because the light weight and strength of PET allows more product to be delivered with less packaging weight and less fuel than most other container materials.
Recyclability - The first PET bottle was recycled in 1977. Nowadays, post-consumer containers are collected from households and processed to make raw material for new applications. Best of all, PET is recyclable and highly sustainable. It is the most recycled plastic. PET can be recycled back into containers for foods, beverages and personal care products - or into carpet, clothing, automotive parts, construction materials, industrial strapping, polyester polyol and other products.
