25 YEARS ANNIVERSARY 12 PETplanet Insider Vol. 25 No. 05/24 www.petpla.net 25 YEARS ANNIVERSARY The material of choice for sustainable packaging based on an article by Dr Frank Welle, The Facts about PET PET (Polyethylene Terephthalate) was first developed for use in synthetic fibres 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 fibres, 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. Bottle now represent the most significant use of PET moulding resins. Making a PET bottle starts from the raw material: ethylene and paraxylene. These two substances’ derivatives (ethylene glycol and terephthalic acid) are made to react in order to obtain the PET resin. The resin, in the shape of small cylinders called pellets, is melted and injected into a mould to make a preform. The preform - a sort of test tube, shorter than the final bottle but with thicker walls - is then blow-moulded. During the blow-moulding phase, high-pressure air is blown into the preform allowing it to take the exact shape of the mould it is set into. The final product is, thanks to the molecular structure of the material, a transparent, unbreakable, resealable and lightweight bottle. The strength of the material It is the strength of the material that contributes to the success of PET. Indeed, carbonated soft drinks can generate pressure inside the bottle reaching up to 6 bar. Such high pressure however, thanks to the alignment of macromolecules (crystallisation) occurring both during the resin spinning process and the blow-moulding process, is not capable of deforming the bottle nor can it make the bottle explode. Another advantage of the material lies in its physical properties that allow for great freedom in design. Throughout the years, the PET industry has increasingly taken on environmental concerns, significantly decreasing the quantity of raw material needed for the manufacture of bottles. Nowadays, a 1.5 l PET container is manufactured with < 30 g of raw material. Another striking feature of PET on the environmental side is that it is fully recyclable. In 1977, the first PET bottle was recycled and turned into a bottle base cup. Soon however, the fibre industry discovered the “new” material source and started using it for making textiles, carpets and non-wovens. Today, even though the “bottle to bottle” recycling process is growing, the fibre market is still the major outlet for recovered PET. Lightweighting PET PET bottles are very strong, colourless and lightweight. PET is transparent and it allows the content of the container to remain visible. The strength and lightweight of PET is very important for beverage packaging since it makes the bottles safe for on-the-go or sports use. Over the years, the weight of PET bottles has been reduced and today a 1.5 l bottle can weigh as little as 20 to 30g. This process of light weighting represents a true benefit with regard to the environmental performance a bottle will have during its lifetime: production, transport to the consumer and end of life cycle. With its excellent material properties, PET is widely used today as a packaging material for liquids such as carbonated beverages and is one of the most suitable materials for the packaging of natural mineral and spring water. PET is used in the packaging sector in the form of films, trays or bottles, its principle use being in bottles. The interaction of PET with food and water No packaging material is fully inert and so there will always be some kind of interaction with the beverage or foodstuff it contains. In the case of food, mild oxidation may occur due to oxygen permeation. Likewise, carbon dioxide from carbonated beverages can permeate through the packaging material. In certain instances, there may also be a small degree of migration of components from the plastic packaging into the content. For consumer health protection, all such interaction must be reduced to a minimum. As with all other material in contact with food, PET packaging does comply with all European and national legal requirements. Such requirements include an assessment of the initial raw materials employed (i.e., monomers and additives) and the compliance with any restrictions that are established, such as migration limits. The requirements for the migration of monomers and additives according to the European Packaging Legislation is given in Table 1. Acetaldehyde Acetaldehyde is a by-product of the PET manufacturing process. It is produced when PET is heated to a high temperature to produce bottles. Many beverages and foodstuffs contain natural acetaldehyde. The trace quantities of acetaldehyde that may migrate from PET into bottled water are totally harmless, although they may cause the water to have a slightly fruity offtaste. When the concentration exceeds 0.02mg of acetaldehyde per litre, the consumer may be able to taste it. Based on consumers’ acceptance and local regulation, this is something that should be avoided in some countries whereas it is well accepted in others. PET bottle manufacturers have worked closely with the bottled water companies to optimise the PET bottle production process with a view to minimising levels of acet-
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