Polyethylene Terephthalate, commonly referred to as PET (or PETE) is a thermoplastic polymer resin. PET begins as white resin pellets that become transparent when heated and cured into a desired plastic part. We interact with this versatile material in our everyday lives from food and beverage packaging to personal care and beauty containers. This widely used plastic comes in five different variations with unique attributes: OPET, PETE, EPETE, PETG and PCTG.
PETE (or PET)
PETE is the most common variation of the thermoplastic polymer resin. The clarity of PET is considered to be the best of all plastics with very good chemical resistance. PETE is formed into containers via 1-Step or 2-Step Injection Blow Molding.
1-Step IBM is considered optimal to maintain the clarity and finish of the final bottle as the injection molded Preform is transferred immediately to the Blowing station to be formed into the final container, vs. the 2-Step IBM process, where the Preform is often tumble packed for storage and transferred to a different machine for blow molding at a later date, this results in minor abrasions, nicks and scratches that are avoided in the 1-Step process.
Here are some of the advantages of running PETE through a 1-Step process:
- Blemish Free Containers
- Lack of Transfer Ring
- Thread can be orientated with bottle cap
- Inconsistent wall thickness
- Long Cycle Times
PET Preforms are reheated before the Stretch and Blow Stage in 2-Step Injection Stretch Blow Molding
The “O” in OPET stands for oriented. PET is oriented biaxially during the 2-Step Injection Stretch Blow Moulding process. When PET is in the preform stage, the polymer molecule starts as an unbalanced chain, when the polymer is heated and stretched with a pin the molecule is oriented, or arranged, in parallel with the direction it is stretched. After the preform is stretched with a pin it is blown to the dimensions of the final container. Oriented PET has the benefit of increased durability, clarity as well as better barrier properties.
PET Preforms are often tumble packed and stored between the first and second stage in 2-Step Injection Stretch Blow Molding.
PETE is an extrusion grade variation of the base resin PET. The molecular weight is higher in this form of PET allowing a parison extrusion. PET containers that require a handle will often be formed from this variation, for example, the clear orange juice containers with handles you’d find at the grocery store. The chemical resistance and clarity is comparable with PETE.
Polyethylene Terephthalate Glycol (PETG) is an amorphous variation of PET. PETG cannot be oriented and therefore you will not find pre-forms of this type of resin. Extrusion, Injection Blow Moulding and 1-Step Injection Stretch Blow Moulding are all possible for PETG, it is also used frequently for 3D printing. Clarity and chemical resistance are considered good when compared to the previous three variations, however PETG has poor impact resistance.
PCTG is another amorphous form of PET. Like PETG, PCTG cannot be oriented, it is suitable for Extrusion, Injection and 1-Step Injection Stretch Blow Moulding. Due to its excellent impact resistance and clarity it is commonly used for products requiring higher impact resistance. PCTG resin is used often in cosmetic packaging components.