Polyethylene terephthalate
type of polyester commonly used for bottles and clothing
Polyethylene terephthalate (or poly(ethylene terephthalate), PET, PETE, or the obsolete PETP or PET-P) is the most common thermoplastic polymer resin of the polyester family and is used in fibres for clothing, containers for liquids and foods, and thermoformed parts for manufacturing, and in combination with glass fibre for engineering resins.
In 2025, annual global production of PET was 31 million tons with 2031 projections showing over 40 million tons. In the context of textile applications, PET is referred to by its common name, polyester, whereas the acronym PET is generally used in relation to packaging. PET used in non-fiber applications (i.e. for packaging) makes up about 6% of world polymer production by mass. Including the >60% fraction of polyethylene terephthalate produced for use as polyester fibers, PET is the fourth-most-produced polymer after polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC).
PET consists of repeating (C10H8O4) units. It is commonly recycled, and has the digit 1 (♳) as its resin identification code (RIC). The National Association for PET Container Resources (NAPCOR) defines PET as: "Polyethylene terephthalate items referenced are derived from terephthalic acid (or dimethyl terephthalate) and mono ethylene glycol, wherein the sum of terephthalic acid (or dimethyl terephthalate) and mono ethylene glycol reacted constitutes at least 90 percent of the mass of monomer reacted to form the polymer, and must exhibit a melting peak temperature between 225 °C and 255 °C, as identified during the second thermal scan in procedure 10.1 in ASTM D3418, when heating the sample at a rate of 10 °C/minute."
Depending on its processing and thermal history, polyethylene terephthalate may exist both as an amorphous (transparent) and as a semi-crystalline polymer. The semicrystalline material might appear transparent (particle size less than 500 nm) or opaque and white (particle size up to a few micrometers) depending on its crystal structure and particle size.
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