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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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Sustainability concerns
Microplastics
Polyethylene terephthalate (PET) is uniquely placed as a recyclable material. Its use in packaging containers, in particular drinks bottles, provides a reliable and steady stream of high quality recyclable material. In addition, the molecular structure and chemistry of PET mean it maintains stable crystallisation, thermal and mechanical properties throughout recycling, which are often closely comparable to virgin material. Therefore, it can be used as a direct replacement in many cases.
rPET is available as semi-crystalline (opaque) and amorphous (transparent). It is converted back into packaging – rPET is available that can be used in food contact applications – as well as textiles for fashion and moulded automotive parts, for example.
It is a valuable recycled material, desirable for many applications and sought after by companies wishing to reduce their use of virgin material. As a result, it tends to be more expensive.
Some studies have raised concerns about the generation of microplastics during plastic recycling. PCR material is shredded and washed – the water carries tiny fragments of plastics into the environment if not very carefully filtered. It is therefore essential to ensure the source of recycled material is not adding additional negative environmental impacts during processing.
