PET is a type of plastic raw material derived from petroleum, its formula corresponding to that of an aromatic polyester. Its technical name is Polyethylene Terephthalate or Polyethylene Terephthalate. It began to be used as a raw material in fibers for the textile industry and the production of films.
PET (Polyethylene Terephthalate), belonging to the group of synthetic materials called polyesters, was discovered by British scientists Whinfield and Dickson in 1941, who patented it as a polymer for the manufacture of fibres. It should be remembered that their country was in the midst of war and there was an urgent need to find substitutes for cotton from Egypt. It was not until 1946 that it began to be used industrially as a fibre and its use in textiles has continued to the present. In 1952 it began to be used in the form of film for food packaging. But the application that gave it its main market was in rigid containers, from 1976 onwards; it was able to make its way thanks to its particular aptitude for bottling carbonated drinks.
This is the polymer to which international machine manufacturers have devoted the greatest technical and commercial effort. Indeed, manufacturers have specifically designed, and with substantial investments, equipment and complete lines perfectly adapted to the parameters of PET transformation, whose accessible availability to all bottlers, together with the appropriate marketing of the raw material, has allowed the expansion of its use throughout the world.
Properties of PET
- Processable by blow molding, injection molding, extrusion. Suitable for producing jars, bottles, films, sheets, plates and parts.
- Transparency and shine with magnifying glass effect.
- Excellent mechanical properties.
- Gas barrier.
- Biorientable-crystallizable.
- Sterilizable by gamma and ethylene oxide.
- Cost/performance.
- Ranked #1 in recycling.
- Light
Disadvantages
Drying
All polyester must be dried to avoid loss of properties. The humidity of the polymer entering the process must be a maximum of 0.005%.
Cost of equipment
Injection blow moulding equipment with bi-orientation offers good payback for high production. In extrusion blow moulding, conventional PVC equipment can be used, providing greater versatility in the production of different sizes and shapes.
Temperature
Polyesters do not maintain good properties when subjected to temperatures above 70 degrees. Improvements have been achieved by modifying equipment to allow hot filling. Exception: crystallized (opaque) PET has good resistance to temperatures up to 230 °C.
Outdoor
Permanent outdoor use is not recommended.
Advantages
Unique properties
Clarity, brightness, transparency, barrier to gases or aromas, impact, thermoformability, easy to print with inks, allows microwave cooking.
Cost/Performance
The price of PET has fluctuated less than that of other polymers such as PVC-PP-LDPE-GPPS over the last 5 years.
Availability
Today PET is produced in South and North America, Europe, Asia and South Africa.
Recycling
PET can be recycled into the material known as RPET, unfortunately RPET cannot be used to produce packaging for the food industry because the temperatures involved in the process are not high enough to ensure the sterilization of the product.
Features of PET
Biorientation
It allows to achieve mechanical and barrier properties with thickness optimization.
Crystallization
It allows thermal resistance to be achieved for using thermoformed trays in ovens at high cooking temperatures.
Sterilization
PET resists chemical sterilization with ethylene oxide and gamma radiation
Ecological alternatives
- Returnability
- Reuse of grinding
- Fibers
- Polyols for polyurethanes
- Unsaturated polyesters
- Non-food packaging
- Alcoholysis/Methanolysis
- Incineration.
TECHNICAL DATA
| Viscosity limit value measured in dichloroacetic acid at 25°C | 1.07 |
| Melting point °C | approx. 252/260 |
| Acetaldehyde | ppm < 1 |
| Carboxylic group content | mval/kg 20 |
| Apparent density [g/cm 3 ] approx. | 0.85 |
Permeability values
| Oxygen 23°C, 100% RF | 2 |
| Nitrogen 23°C, 100% RF | 9 |
| Water vapor permeability | 0.9 |
| Carbon dioxide | 5.1 |
Chemical resistance of PET
Good general resistance especially to:
Fats and oils present in foods, dilute solutions of mineral acids, alkalis, salts, soaps, aliphatic hydrocarbons and alcohols.
Little resistance to:
Halogenated solvents, aromatic solvents and low molecular weight ketones.
Some applications of PET
Packaging
Manufactured by injection or blow molding with biorientation, by extrusion or blow molding.
Uses : soft drinks, toothpastes, lotions, powders and talcum powders, waters and juices, shampoos, wines, edible and medicinal oils, hair products, drugs, food industry and cosmetics and pharmaceutical laboratories.
Sheets and films
Manufactured by flat extrusion or bubble coextrusion. Bioriented films.
Uses : boxes, blisters, pouches for packaging food, medicines, cosmetics.
Others
Injection parts, manufacturing of engineering plastics used for cases of high thermal and mechanical demands.
Uses : Manufacture of engine casings, containers resistant to freezing and subsequent autoclaving, temperature-resistant monofilaments in acidic media.