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PET - What is it and What is the Influence of PET on Beverages?
PET - what sort of material is it?
The plastic PET is a polyester, chemically known as PolyEthylene Terephthalate. This plastic has established itself worldwide as a material for the production of drink bottles.
As a so-called thermoplastic it offers numerous advantages because it is easily moldable and thus allows production of individual bottle shapes, specifically designed as non-returnable items. Further advantages for the consumer are its stability and lightweight. In addition bottles can be made completely from PET, which simplifies recycling considerably.
Via numerous technical measures it has been possible to optimize PET bottles more and more in recent years, enabling advancements such as the production of returnable and hot-fill PET bottles. Through modification of the manufacturing process the so-called crystallization level can be increased. The higher the crystallization, the better the properties of PET in relation to gas permeability and resistance to heat and aggressive materials.
The disadvantage is that PET becomes increasingly brittle and opaque at increasing crystallization levels. Extremely crystalline PET is effectively white. This can be clearly seen on the neck of some returnable bottles already in the market.
A further optimization has been the use of another plastic, PEN (PolyEthylene Naphthalate), in manufacturing bottles. This plastic displays considerably better barrier properties than PET, but is significantly more expensive.
In the next issue we will deal with the influence of these materials on beverages.
PET - what is its influence on beverages?
Gas permeability is a major difficulty here, as it can lead to problems within the beverage. Because these processes occur as diffusion, independent of pressure, even a carbonated beverage takes up oxygen and at the same time releases carbon dioxide. The intruding oxygen can damage beverage ingredients, in particular vitamins and flavors.
In addition, PET can absorb flavor components of the beverage. This is a result of the structure of the plastic. The long polymer molecules are tangled within each other like a sponge. In this "sponge", flavor components are stored and later released again. When the crystallization level increases, this sponge structure becomes "untangled" and less foreign material may be absorbed. This has made the development of returnable PET bottles possible, despite the possibility of flavor absorption. At the same time, crystallization of the material also improves its resistance to heat, so that hot-fill PET bottles can also be produced using the same technology.
However, these disadvantages mean that the shelf life of a beverage in PET is usually shorter than in glass bottles. But through appropriate recipe design, the manufacturer of flavor systems can offset many of the disadvantages of PET.
