What is Polyester?

PET is short for polyethylene terephthalate, the chemical name for polyester. 

PET is a clear, strong, and lightweight plastic that is widely used for packaging foods and beverages, especially soft drinks, juices, and water. 

It is also popular for packaging food and special grades of PET are used for carry-home food containers and prepared food trays that can be warmed in the oven or microwave. 

The basic building blocks of PET are ethylene glycol and terephthalic acid, which are combined to form a polymer chain. The resulting spaghetti-like strands of PET are extruded, quickly cooled, and cut into small pellets. The resin pellets are then heated to a molten liquid that can be easily extruded or molded into items of practically any shape.

PET was first synthesized in North America in the mid-1940s by DuPont chemists searching for new synthetic fibres. DuPont later branded its PET fiber as "Dacron." Today, more than half of the world's synthetic fibre is made from PET, which is called "polyester" when used for fibre or fabric applications. When used for containers and other purposes, it is called PET or PET resin. 

In the late 1950s, researchers found a way to stretch a thin extruded sheet of PET in two directions to create PET film, which is now used extensively for video, photo, and packaging films. In the early 1970s, the technology was developed for blow-stretch molding PET into bottles. 

What is polyester film and what can it be used for?

Polyester is a versatile plastic film that excels in having an exceptional combination of high tensile strength, chemical resistance, thermal stability, flatness, high temperature resistance and thermal and electrical insulation properties. In addition, translucent polyester in this state offers excellent clarity and gloss. 

Polyester is also known as Biaxially Oriented Polyethylene Terathalate (BOPET). The name “PET” is the common abbreviation for the chemical name “polyethylene terephthalate” and biaxially oriented means that the film has been stretched in both the machine and transverse directions making it stable. 

Biaxially oriented PET film can be metallized by vapor deposition of a thin film of evaporated aluminium onto it. The result is much less permeable to gases (important in food packaging) and reflects up to 99% of light, including much of the infrared spectrum. For some applications like food packaging, the aluminized BOPET film can be laminated with a layer of polyethylene, which provides sealability and improves puncture resistance. 

BOPET film is also available in white which is often used for yoghurt pot lids and in ‘hazy’ which gives a matt finish. 

What can polyester packaging film be used for?

Polyester can be used as a single web film or as part of a laminate structure. 

Single web

We are probably most aware of single web polyester being used as the lidding film on ready meals. It easily seals to PET trays and can be made to peel off rather than needing to be cut with a knife. As polyester is heat resistant the tray and the lidding still intact can be placed in an oven and the product cooked in the packaging.

Polyester is also used extensively for produce punnet lidding and often has ‘hole punch’ holes made in the film or can have micro-perforations to allow gas to escape extending shelf life.

Single web polyester is also used for food on the go where the product is heated in an oven in supermarkets or service stations. It can be perforated to allow steam to escape which is particularly useful for sausage rolls, pies, and crispy rolls where it is better for any steam to escape. 

It can also be used for part cooked bakery items that can be ‘finished off’ in store whilst still in the packaging. Often used for frozen products. The products can be made a long time in advance at the manufacturers, frozen and then sent to store to be defrosted and ‘cooked’ in the oven, giving that just cooked smell attracting shoppers.

Where the perforated pack needs to go into an oven and the polyester is printed, special inks must be used to prevent the ink migrating to the food and our product is fully certified for this. 

Laminate

Used in a laminate the polyester retains its barrier properties but not always its heat resistance properties. 

For example, laminating it to PE (polyethylene) will mean that it can no longer go into the oven, as the PE would melt. However, this property of PE makes it an excellent heat-sealing layer where the polyester is there for barrier or for its high gloss. This laminate has many variations but is a popular structure for many food products for example powders and free flowing products like pulses and nuts.

The polyester on the outside of a pack gives a glossy finish especially when it has been reverse-printed and the inks (the design) are viewed through this glossy film.

The polyester used in laminates is usually just 12 microns making it the most cost-effective option, even over polypropylene.

Polyester film can also be supplied with Post Consumer Recyclate (PCR)  included which makes the film exempt from the Plastics Tax.

What is rPET?

While all PET is fully recyclable, rPET has the extra benefit of being made with recyclable material. Up to 80% of the rPET contains raw materials of recycled PET reducing the polymer and oil raw material used to manufacture. 

The extra benefit to using rPET is that not only is it predominately made from recycled material, but it uses less energy to make an rPET tray than it does to make a virgin PET. 

What is APET?

Otherwise known as amorphous polyethylene terephthalate APET, is a type of PET and one of the best clear plastic materials for thermoformed packaging. 

APET is highly shiny and transparent clear plastic packaging.  Its optimum use is for displaying food and non-food products on-shelf visual merchandising in retail. 

Polyester is a hard -working film and can be used in many different packaging formats.

31 | 03 | 2021