August 10, 2020
Understanding Polyester Alternatives
Here’s a polyester primer for differentiating the sustainable options designers have when specifying these ubiquitous plastics.
Polyester is a material that everyone has heard of but few understand: It is actually a family of polymers that encompasses applications like bioplastics, the clear stiff soda bottle, and the resin used in fiber-reinforced composites for massive wind turbines. To ensure you can make an informed decision when a vendor talks up an amazing new product, here are the predominant types:
PET, PETE, and APET, in water bottles, fabrics, and carpet fibers: The most common of the polyesters.
PTT, the new carpet fiber:
Polytrimethylene terephthalate combines the best properties of nylon and polyester and is now being used in carpets and other home furnishings, as well as in automotive fabrics.
PET-G, in transparent interior panels: This version doesn’t “haze” or crystallize, maintaining the appearance of the material over time. Unfortunately, it is also a little easier to scratch, so it’s recommended that you leave the protective liner on until installation is complete.
PBT, in electrical parts and lighting: Familiar to lighting designers and prevalent in HVAC and electrical components, polybutylene terephthalate is the workhorse polyester thanks to its greater resistance to heat, corrosion, and UV radiation.
Because of PET’s ubiquity—it accounts for 13 percent of all plastics on the planet—there has been a lot of work on developing nonpetroleum-based versions, with some success. The two chemicals that make up polyester, 70 percent purified terephthalic acid (PTA) and 30 percent monoethylene glycol (MEG), can be made from natural sources, though bio-based PTA is somewhat more expensive. That’s why your PlantBottle currently uses only 30 percent bio-based sources—the MEG part—despite earlier intentions to use 100 per- cent biological sources.
Even though water and soda bottles account for only 25 to 28 percent of all PET, their easy availability makes this form of post-consumer recycling the most effective among plastics. Recycled PET from bottles is great for making fabrics and molded furniture—hello, Emeco 111 Navy Chair—and there remains a good supply of it, whether from a New York curbside pickup or a beach in Haiti.
The big advantage of bio-based PET is that it can be recycled with oil-based PET with no loss of performance or value.
Other polyesters, like PBT and PTT, cannot be recycled with PET, and manufacturers cannot put the “1” recycling symbol on anything that is not APET. There are companies, however, that will take those plastics if you have sufficient volume and the materials are “clean” (i.e., with no paint or attachments and not too weathered from sunlight).
Andrew Dent is the EVP of materials research at Material ConneXion and chief material scientist at SANDOW.
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