Polyethylene terephthalate (or poly(ethylene terephthalate), PET, or PETE) is the polyester family's most common thermoplastic polymer resin. PET has a glass transition temperature of 67–81 °C and a melting point of 260 °C.
Polyethylene terephthalate has high strength and stiffness. It exhibits excellent electrical insulating properties. It is very lightweight. It has good gas (oxygen, carbon dioxide) and moisture barrier properties. It has a broad range of use temperatures, from -60 to 130 °C. PET has low gas permeability, particularly with carbon dioxide.
Polyethylene terephthalate is suitable for transparent applications, when quenching during processing. It doesn’t break or fracture. It is shatterproof, recyclable, and transparent to microwave radiation.
The advantages of Polyethylene Terephthalate as a material are that it is shatterproof, is non-reactive when in contact with food or water, and provides a high strength-to-weight ratio. Being lightweight also provides for cost savings when transporting products using PET packaging.
The glass conversion temperature of PET is about 165℃, and the temperature range of the material is 120~220℃. PET has a strong hygroscopicity at high temperatures. For glass fiber reinforced PET materials, bending deformation is very easy to occur at high temperatures. The material liquefies at high temperatures (as opposed to burning) also makes it an ideal material for recycling. Hence it is considered to be a green plastic.
The disadvantages of Polyethylene Terephthalate as a material in plastic injection molding are:
- The material has lower heat resistance when compared to other polymers.
- Resins made from PET can oxidize, resulting in a degradation in the taste of food and beverages when the items have a long shelf life and are stored in PET packaging.
- PET is not a biodegradable plastic, which may be a disadvantage depending on the intended application.
Injection molding is mainly used to enhance the molding of PET. In general, PET can only be molded by a screw-type injection molding machine.