Polyethylene terephthalate is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination with glass fiber.
PET bottles account for 30% of the material demand. It contains the chemical elements carbon, hydrogen, and oxygen. If fully burned, it produces only carbon dioxide and water. For specialist bottles polyvinyl alcohol is sandwiched with PET to educe its oxygen permeability.
When produced as a thin film, PET can be coated with a thin film of aluminum metal to reduce is permeability, and to make it reflective and opaque.
When PET degrades, several things happen: discoloration, chain scissions resulting in reduced molecular weight and formation of acetaldehyde. Which is a colorless liquid with a fruity smell. It forms naturally in fruit, but it can cause an off-taste in bottled water. When acetaldehyde is produced it altering the taste and aroma. For bottled water, low acetaldehyde content is quite important, because if nothing masks the aroma, even extremely low concentrations (10-20 parts per billion parts of resin, by weight) of acetaldehyde can produce an off-taste.
One way to alleviate this is to use a copolymer which lower the melting temperature and reduces the degree of crystallinity of PET (especially important when the material is used for bottle manufacturing). Thus the resin can be plastically formed at lower temperatures and/or with lower force. This helps to prevent degradation, reducing the acetaldehyde content of the finished product to an acceptable (that is, unnoticeable) level.
Bottle processing equipment
Most common manufacturing involves a perform, which looks like a test tube with bottle threads already in place, its placed into the blow mold where the shape is created as its inflated between the moulds two parts. This is a two step process. With a one step process where raw materials is put into the machine is used for non standard shapes.