PET is used worldwide to make containers for beer, wine, other alcoholic beverages, carbonated soft drinks, water, juices and nectars, consumer products ranging from medicines to household cleaners, food and dairy products, and industrial products ranging from oils to chemicals.
Like all polymers, PET molecules consist of long chains of repeating units containing carbon, oxygen and hydrogen.
What we now know as PET was first developed for use in synthetic fibres by British Calico Printers in 1941.
Although originally produced for fibres, PET began to be used for packaging films in the mid 1960s and then, in the early 1970s, the technique for ‘blowing’ bottles was commercially developed and the PET container industry that we know today was born. The manufacture of bottles, jars and other containers – rather than fibres – is now the largest user of PET resins.
Making PET containers
Making PET starts with the raw materials ethylene and paraxylene – or, more accurately, with their derivatives, ethylene glycol and terephthalic acid. These are made to react under high temperature and low vacuum pressure to form a polymer chain that is PET resin.
The resin, usually in small cylinders called pellets, is melted and injected into a mould to make a preform – a test tube shape that is smaller than the finished container that it will become but with thicker walls. The preform is then blow-moulded by injecting high-pressure air that forces the material into the exact shape of the mould in which it is placed.
Strength and versatility
The strength of the material is one of the reasons that PET is ideal for the production of containers.
Carbonated soft drinks can generate pressure inside the bottle reaching up to 6 bar. Even this high pressure is not capable of deforming the bottle, however, as a result of the alignment of PET macromolecules (crystallisation) which occurs both during the resin spinning process and the blow-moulding process.
In addition to being strong, PET is lightweight, shatterproof and retains freshness when used to contain food or drink. It is resistant to attack by micro-organisms and does not react with food products, which is why it is widely used for packaging foods, beverages and pharmaceuticals.
PET also has environmental benefits when compared to other materials and is completely recyclable.
Health and chemicals
PET does not contain Bisphenol-A (BPA), a compound used to make polycarbonate, (a different type of plastic found in some baby bottles, the lining of metal cans, water cooler bottles and reusable sports bottles). Some legislators and consumer groups have called for a ban on BPA in children's and infant products, citing a possible connection to developmental and reproductive disorders.
PET contains no phthalates. Plasticiser phthalates are sometimes used to soften other types of plastic and some people believe these may be endocrine disruptors. Nor does PET contain dioxins, a group of compounds sometimes formed with high-temperature combustion and certain industrial processes involving chlorine.
Health and regulatory agencies around the world, including the US Food & Drug Administration and the European Food Safety Authority, have declared PET to be safe for food and beverage use.
Other uses
PET is usually called ‘polyester’ when used for fibres or fabrics. More than half of the world's synthetic fibre is made from PET.
PET film is used extensively as video, photographic and X-ray film as well as for packaging.
PEN
We are working not just with PET but also with PEN (PolyEthylene Naphthalate), a polyester which provides a very good oxygen barrier. It is therefore particularly well-suited for bottling beverages such as beer that are susceptible to oxidation and for containing some pharmaceutical and chemical products where protection from the atmosphere is important.
Plant-based resins
We are leading the industry in our use of blends of PET and plant resins which can offer further environmental benefits.
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