Polyethylenterephalat (PET)

PET is widely known as polyester and is often associated with the term "PET bottle". It was first developed in the USA in the early 1940s for the production of synthetic fibres as an alternative to silk and is still a common component in textiles today. At the beginning of the 1960s, another large field of application for this plastic was opened up with the start of the production of so-called polyester films. From the beginning of the 1970s, the blow moulding of hollow bodies - especially bottles and containers - became the third major area of application.

A distinction is essentially made between two groups. The group known as A-PET (amorphous) has a low crystallinity with a rather low melting point and can be processed over a wide temperature range without the risk of melt fracture, i.e. breakage when deformed under heat.
A-PET is mainly used for transparent, thermoformed trays, containers or bottles as packaging for food, cosmetics or chemical-technical products.

The group known as C-PET (crystalline), on the other hand, has a high crystallinity with a high melting point of over 280 ° C and is characterised by high gloss and good transparency.
Films made of C-PET are well suited for thermoforming containers, trays or trays, which have the property of dual ovenability, i.e. heat resistance when used in convection ovens and microwave ovens.


The petrochemicals P-dimethylbenzene and ethylene serve as raw materials. Terephthalic acid dimethyl ester and ethylene glycol are produced from these. There are two processes for the production of PET. In the polycondensation process, PET is obtained from terephthalic acid and diethylene glycol by splitting off water.

The second and most commonly used process is the transesterification of dimethyl terephthalate with ethylene glycol, splitting off methanol. The reaction takes place under heat at temperatures between 260 and 270 ° C. In a further step, any remaining small amounts of water are reduced to small residual values of less than 0.01 % by reheating for several hours. On the one hand, this prevents hydrolytic degradation of the end products, and on the other hand, the mechanical properties improve significantly due to the polycondensation that continues at this stage. PET is often chemically modified to influence the crystallisation and thus the melting point.

By applying specific processes, different grades of PET are obtained, which differ in their properties with regard to their melting point and processability.

Polyester films have very low permeabilities for water vapour, oxygen and flavouring substances, but not yet low enough for sole use as barrier films. They do not contain plasticisers and are physiologically harmless. In addition, they are odourless and tasteless and are resistant to most organic chemicals, solvents, fats and oils.

The property profile of polyester films is excellently suited for many areas of application and can be specifically adapted to the respective application by modifying the starting material polyethylene terephthalate and the manufacturing process. Possible applications include, for example, photographic films in photography, magnetic tape films for magnetic recordings, microfilms and films in reprography, electrical insulation films and capacitor films in electrical engineering, and a wide range of applications in packaging technology. Here, polyester films are often used in combination with PE due to their good mechanical properties and high temperature resistance. Additional barrier layers made of EVOH (ethylene/vinyl alcohol copolymer), for example, can be incorporated into the composite.


Polyester films are generally produced by flat film extrusion. After extrusion, the film is cooled down quickly to achieve the finest possible crystalline state of the polymer. This is often followed by further processing in a stretching process to produce oriented polyester films, the so-called BOPET films (biaxially oriented). This results in a significant increase in the crystallinity of the film. Further crystallisation and, in particular, fixation of the film structure is achieved by reheating. This process leads to an excellent development of the mechanical properties with the result that the oriented polyester films have particularly good tear, impact and abrasion resistance as well as excellent toughness. The optical properties are sufficiently good. Outstanding are the thermal properties regarding cold and heat resistance (about -70 °C to 150 °C) even during prolonged use. Especially because of their good temperature resistance, polyester films are increasingly used as packaging for microwave applications.


Important applications for polyester films or laminates are the use as cooking bags, menu trays with dual-ovenability, baking films in the household or films for medical packaging. Another advantage of polyester films is their excellent suitability for metallising and printing. The most outstanding properties of PET are its excellent temperature resistance and its outstanding mechanical properties. The optical properties are satisfactory.

Furthermore, PET has good barrier properties with low permeabilities for gases, water vapour and aromas. However, the barrier values are not sufficient as a stand-alone barrier film. However, it is very suitable as a composite with other plastics such as preferably PE and incorporated barrier layers of gas or plastics such as EVOH and can be easily metallised as a supplementary coating. Furthermore, it is odourless and aroma-neutral, resistant to organic chemicals, solvents, fats and oils, and physiologically harmless.

PET surpasses all other plastics in terms of the versatility of its applications.

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