Most thermoplastic polyesters are based on polyethylene terephthalate (commonly abbreviated to PET, PETE or the obsolete PETP or PET-P) or polybutylene terephthalate (PBT).
Engineering thermoplastic polyesters are performance polymers. As a class, they combine excellent mechanical, electrical and thermal properties with very good chemical resistance. Polyesters also offer low moisture absorption (especially in comparison to in nylons (polyamides) and, therefore, exceptional dimensional stability. They also have good flow properties.
PET is the most common thermoplastic polymer resin of the polyester family. The majority of the world’s PET production is for synthetic fibers for clothing (in excess of 60%), with containers and bottles for liquids and foods accounting for about 30% of global demand. In total, PET makes up about 18% of world polymer production and is the fourth-most-produced polymer after polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC).
Polybutylene terephthalate is the second most important commercial polyester. It is a semi-aromatic thermoplastic that can be easily molded and thermoformed. Compared to PET, PBT has slightly lower strength and rigidity, slightly better impact resistance, and a slightly lower glass transition temperature. PBT and PET are both sensitive to hot water above 60°C. Both need UV protection if used outdoors, and most grades of these polyesters are flammable, although additives can be used to improve both UV and flammability properties.
More than 50% of demand for PBT and filled or reinforced PET is in molded electrical connectors, switches, and relays for automobiles and, to a lesser extent, printed circuit boards. This market is in transition as new forces drive up temperature requirements — notably miniaturization, increased crowding of automotive components under the hood, and newer lead-free soldering methods.
Due to the semi-crystalline nature of polyesters, the resistance to chemical attack and environmental stress crack resistance are exceptional, particularly in comparison to polycarbonates (PC).
Other properties of note:
- Very good heat and heat aging resistance
- Very low creep, even at elevated temperatures
- Very good color stability
- Excellent wear
Hydrolysis-resistant PBTs translates into improved warp and heat resistance. They allow connectors to meet global standards without redesign and retooling of existing connectors for a different polymer, albeit at a price premium.
Blends of PBT/PET and PBT/PC are common. A new PBT/PET blend for lightweight headlamp bezels is an improved version of the 20% mineral-reinforced grade currently used in headlamps. The new version boasts improved flow to allow for thinner walls.
Medical-grade PBTs are available and notably used in declutch tubes for an IV-therapy syringe, replacing five metal components. PBT can also be made into yarn. This has a natural stretch similar to Lycra and can be incorporated into sportswear. Due to its chlorine resistance, it is commonly found in swimwear.
Other thermoplastic polyesters are commercially available too.
Polytrimethylene terephthalate (PTT): a recently launched novel polyester for injection molding and extrusion. It is more easily processable and less prone to moisture pick-up than PET, while its mechanical properties are between those of PET and PBT. A catalyst breakthrough has made PTT a cost-effective alternative to PET and PBT, especially for carpet face and textile fibers, where it offers outstanding resilience, stain resistance, and color vibrancy. PTT can also be extruded into biaxially oriented films: A PTT/PET blend could replace PVC in shrink film for industrial bundling of bottles.
PETG and PCTG: glycol-modified copolyesters. PETG has long been extrusion blow-molded into relatively small, simple bottles such as refrigerator containers. New grades are opening the way for polyesters to penetrate tougher, thicker and larger extrusion blown parts.
PCT: increasingly used in electrical devices because they offer short-term heat resistance between that of PBT and liquid crystal polymers (LCP).
PCTA: an isophthalic acid-modified PCT tailored for injection and stretch-blow molding. One grade is said to reduce cycle times in thin-wall injection moldings (lower-cost PET crystallizes so quickly in wall sections thicker than 3mm that hazing results).
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References
- https://www.bpf.co.uk/plastipedia/polymers/polyesters.aspx
- https://www.ptonline.com/articles/thermoplastic-polyesters-it’s-a-good-time-to-know-them-better
- https://polymerdatabase.com/Polymer%20Brands/PBT.html
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Hi, Sir
I am looking for PBT 15%GF and PPS 40%GF Beige (similar with the FZ3600 PPS FDA) with FDA and EU10/2011 certified.
Are you able to recommend any supplier or substitute materials.
Hi Pang
Not off the top of my head, but the Prospector should be able to help! If not, other readers. Happy to take it on as a research project if you want to contact me privately.