Polyethylene terephthalate (PET), also known as polyester, is a clear, strong and lightweight thermoplastic polymer plastic that is widely used for the production of polyester fibres and various packaging applications, from foods to consumer products.
PET is produced from high purity ethylene glycol (EG) and terephthalic acid (TPA). EG is a colorless liquid obtained from ethylene, and TPA is a crystalline solid obtained from xylene. The manufacture processes are as follows:
TPA is mixed with EG and catalyst solution in a paste and fed into the esterification system. The esterification occurs by splitting off water in atmospheric pressure.
The product from esterification step is sent to the pre-polycondensation unit where the reaction takes place under vacuum.
The pre-polycondensation product is fed to the final polycondensation reactor which operates under raised temperature and vacuum.
4) Pelletization & Crystallization
The polyester melt is processed either into fibres / filaments or sent to the solid state polycondensation (SSP) unit to make bottle grade chips.
It can be noted that the first part of the manufacturing process consists of melt phase reaction used to produce copolymers with an intrinsic viscosity (IV) suitable for textile applications. But when very high molecular weights are desired, as is the case for bottle grade PET resins, the polymerization may be carried out in stages.
PET usually incorporating glass fibre reinforcement has been used extensively in automotive body mouldings, tire yarns, bumpers and housings.
Plastics for Packaging
PET resin (excluding textile grade PET resin) is predominantly used for making bottles. An estimated 96-97% of PET resin goes into making bottles for various applications. Even in bottling applications, there are various sub-categories based on the end use.
Moreover, PET sheets are widely used in packaging a range of products such as consumer products, pharmaceuticals, food & beverages, engineering items. Transparent packaging for food is made of PET sheets.
PET is used in fiber applications. PET is widely used in textiles, and is commonly called “polyester.” Polyester is the dominant fabric in the world today, and is used for a wide variety of applications such as clothes, ropes, carpets, upholstery, seat belts.
PET monofilament is mainly used for making mesh fabrics for screen-printing, filter for oil and sand filtration, bracing wires for agricultural applications (greenhouses etc.), woven/knitting belt, filter cloth, and other such industrial applications.