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PET was
first developed for use in synthetic fibers by British
Calico Printers in 1941. The patent rights were then
sold to DuPont and ICI who in turn sold regional rights
to many other companies. Although originally produced
for fibers, PET began to be used for packaging films in
the mid 1960s and then, in the early 1970s, the
technique for blowing bi-axially oriented bottles was
commercially developed.
Bottles
now represent the most significant use of PET molding
resins.
The
manufacturing of a PET bottle starts from the raw
material: ethylene and paraxylene. These two substances'
derivatives (ethylene glycol and terephthalic acid) are
made to react to obtain the PET resin. The resin, in the
shape of small cylinders called pellets, is melted and
injected into a mold to make a perform. The perform, a
sort of test tube shorter than what the bottle will be
but with thicker walls, is then blow-molded. During the
blow-molding phase, high-pressure air is blown into the
perform allowing it to take the exact shape of the mould
it is set into. The final product is a transparent,
strong, and lightweight bottle.
It is
the strength of the material that contributes to make
PET the success it is. Indeed, carbonated soft drinks
can generate pressure inside the bottle reaching up to 6
bar (125 PSI). Such high pressure however, thanks to the
alignment of macromolecules (crystallization) occurring
both during the resin spinning process and the
blow-molding process, is not capable of deforming the
bottle nor can it make the bottle explode.
Throughout the years, the PET industry has increasingly
taken on environmental concerns, significantly
decreasing the amount of raw material needed for the
manufacture of bottles. Nowadays, a 1.5 liter PET
container is manufactured with just 35 grams of raw
material!
Another
striking feature of PET on the environmental side is
that it is fully recyclable. It was in 1977 that the
first PET bottle was recycled and was turned into a
bottle base-cup. Soon however, the fiber industry
discovered the "new" material source and started using
it for making textiles, carpets and non-wovens. Today,
even though the "bottle to bottle" [and bottle to other
packaging products] recycling process is growing, the
fiber market is still the major outlet for recovered
PET.
PET
containers form part of everyone’s daily life; they
contain water, soft drinks, and many other sorts of
liquids as well, such as detergents or soap. [Also, many
vegetables, bakery products, and processed foods are
packaged in PET containers.]
The
main reason lying behind the success of PET containers
is that, thanks to the molecular structure of the
material set into a web, it is unbreakable. Furthermore,
PET packaging is lightweight, transparent, re-sealable,
and inert to the attack of substances present in
food-products such as acids, bases, and fats.
Another
advantage of the material lies in its physical
properties that allow for great freedom in product
design.”
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