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Thermoplastic polyester
2-8 usd/kg
Thermoplastic polyester offers an amazing balance of properties considering its very low price. As a result, it dominates in textiles, films and engineering. The most important of this group is polyethylene terephthalate (PET, PETE) – a low cost plastic available in many formats and commercially significant in many industries. While they have moderate mechanical properties, they have some in-built resistance to weathering, chemicals and fire; which can be enhanced. As a packaging material polyester provides a barrier against water, CO2, oxygen and nitrogen – perhaps the most iconic use of this material is in plastic drinks bottles.
At high temperatures polyester is very sensitive to moisture and particularly vulnerable to water at over 60 degC. Copolyesters have been developed to overcome this shortfall and grades are available that are able to be utilised in reusable, transparent, dishwashable food and drink containers, for example. On the other hand, in the case of biodegradable plastics, this weakness may be enhanced to enable composting end of life. When combined with raw materials from biological sources, it is possible to make bio-based biodegradable polyesters that meet the most stringent composting requirements and are suitable for a range of packaging, textile and industrial applications.
Polyester may be partially, or wholly, derived from biomaterials. Certain types, such as polytrimethylene terephthalate (PTT), have biomaterial derived ingredients as part of their fundamental chemistry, which may or may not be advantageous, depending on the source of the material. Polyethylene furanoate (PEF) is 100% bio-based and offers a superior material to PET in many applications. These materials are not biodegradable.
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Amorphous polyethylene terephthalate (APET, PETE) is the same chemistry as semi-crystalline PET. Both are labelled as ‘PET’ – there is no distinction when it comes to recycling. The difference is that the polymer structure remains random and has not become organised (crystalline). As a result, it is transparent and tough, but has lower temperature resistance and reduced mechanical performance.
Synonymous with plastic stretch blow moulded drinks bottles – both disposable and reusable, in particular water, carbonated drinks, milk and juice – PET is one of the few plastics routinely collected and recycled. It is converted back into packaging (often mixed with virgin), or down cycled to make textiles, such as fleece. It is safe for food contact and can be sterilised by ethylene oxide and gamma radiation (not steam). It provides an effective barrier against water, CO2, oxygen and nitrogen, and is used to make thermoformed containers (trays, cups and containers), medical equipment and point-of-sale displays.
While it has moderate strength, it has good resistance to weathering, burning and most chemicals. It is available as transparent, semi-transparent or opaque colour. As an amorphous material, it is easier to process by 3D printing and thermoforming than semi-crystalline PET.
