Introduction
In this post we’ll discuss PET plastic packaging, how it is manufactured and it’s uses but most importantly, how it is recycled. PET stands for Polyethylene Terephthalate and is one of the most common polymers used for plastic packaging.
It is mainly known for its use in the food and beverage industry. PET is used to make carbonated drink bottles, water bottles, plastic jars, vegetable punnets, food trays and strapping tape. It is also used in the textile industry (known as polyester). PET is a strong and durable plastic that can be flexible if stretched thinly.
Modern living has driven the desire for convenience foods in ready-to-prepare and single-serve formats. This has given rise to all sorts of products that could not exist without packaging – like carbonated soft drinks, long life milk, ready meals and household chemicals, even electronic products like computers and TVs that need to work as soon as they’re out the box.
But once it’s performed this function, packaging takes on an entirely different face: it becomes cumbersome waste. By not considering the impact of packaging on the waste stream, the ugly and unwanted perception people have of packaging will continue.
What is PET?
PET is highly flexible, colourless and semi-crystalline resin in its natural state. Depending upon how it is processed, it can be semi-rigid to rigid. It shows good dimensional stability, resistance to impact, moisture, alcohols and solvents.
PET is an aliphatic polyester. It is obtained from polycondensation reaction of the monomers obtained either by:
- Esterification reaction between terephthalic acid and ethylene glycol, OR
- Trans-esterification reaction between ethylene glycol and dimethyl terephthalate
The reaction produces PET in the form of a molten, viscous mass which can be easily spun directly to fibers or extruded or molded into almost any shape.
PET Chemical Formula: (C10H8O4)n
Plastic is often a more efficient material to choose than alternatives. That’s because plastics are incredibly energy efficient to manufacture and because they are lighter than alternative materials. 900g of plastic can deliver 37.8L of a beverage. You’d need 1.3kg of aluminum, 3.6kg of steel, or over 18kg of glass to bring home the same amount of a beverage. Here’s a look at some plastic resins and some of the ways they’re commonly used in packaging applications.
Key applications:
- Because Polyethylene Terephthalate is an excellent water and moisture barrier material, plastic bottles made from PET are widely used for mineral water and carbonated soft drinks
- Its high mechanical strength, makes Polyethylene Terephthalate films ideal for use in tape applications
- Non-oriented PET sheet can be thermoformed to make packaging trays and blisters
- Its chemical inertness, together with other physical properties, has made it particularly suitable for food packaging applications
- Other packaging applications include rigid cosmetic jars, microwavable containers, transparent films, etc.
How PET Packaging is made?
PET is sometimes referred to as polyester and is made from mono-ethylene glycol (MEG) and purified terephthalic acid (PTA), which is derived from crude oil and natural gas.
These two crude oil derivatives are reacted under a controlled set of conditions to form a polymer. Then, in a honey-like form, this polymer is extruded through a die-plate, cast into spaghetti-like strands, and cut into pellets. These pellets are crystallised and polymerised for a second time to increase their strength and to remove volatiles. The resultant FDA compliant pellets are packaged and sent to the plastics converters to make containers.
PET can be easily processed by injection molding, extrusion, blow molding and thermoforming. PET is generally extruded to produce films and sheets (can be thermoformed after) and blow molding is generally used to produce transparent bottles
Blow Molding:
- Blow molding is generally used to produce transparent bottles
- Mold temperature should lie between 10 and 50°C
Injection Molding:
- Melt temperature: 280-310°C
- Mold temperature: 140-160°C to obtain a crystalline PET (for technical applications)
- For transparent applications, mold temperature should lie between 10 and 50°C
- Screw with an L/D ratio of 18-22 is recommended
Extrusion:
- PET is generally extruded to produce films and sheets (can be thermoformed after)
- Extrusion temperature: 270-290°C
Benefits of PET Packaging
PET has numerous important characteristics that make it a valuable plastic. It is a naturally colourless and non-toxic, which means that it is ideal for use in the packaging industry as it allows consumers to see the product contained within and it does not contaminate products.
It can also be easily dyed, as some beverage manufacturers do with their green or brown bottles to resemble glass bottles.
PET is impermeable to liquids, which means that it is perfect for storing drinks under pressure. It also has a high strength to weight ratio, making it ideal as a protective packaging material. It will not shatter like glass jars and bottles, so PET is the most common replacement for these fragile packaging materials.
Due to its lightweight nature, PET is highly economical. Less polymer is needed to create the packaging as it is strong. This results in cheaper transport costs and less energy needed for the manufacturing of PET plastic. It is a widely recycled polymer because it can retain most of its strength and flexibility characteristics after being processed. This makes recycled PET (rPET) a readily-available and inexpensive material. These characteristics and benefits make PET one of the most common plastic packaging materials in the world.
Key advantages and Properties:
- It has a higher strength and stiffness than PBT
- It is very strong and lightweight & hence easy and efficient to transport
- It is known for its good gas (oxygen, carbon dioxide) and moisture barrier properties
- It exhibits excellent electrical insulating properties
- PET has broad range of use temperature, from -60 to 130°C
- As compared to PBT, it also has higher heat distortion temperature (HDT)
- It has low gas permeability, in particularly with carbon dioxide
- PET is suitable for transparent applications, when quenching during processing
- PET doesn’t not break or fracture. It is practically shatter-resistant and hence, a suitable glass-replacement in some applications
- It is recyclable and transparent to microwave radiation
- PET is approved as safe for contact with foods and beverages by the FDA, Health Canada, EFSA & other health agencies
- Excellent resistance to alcohols, aliphatic hydrocarbons, oils, grease and diluted acids
- Moderate resistance to diluted alkalis, aromatic & halogenated hydrocarbons
Limitations:
- Lower impact strength than PBT
- Lower moldability than PBT, due its slow crystallization rate
- Affected by boiling water
- Attacked by alkalis and strong bases
- Attacked at high temperatures (>60°C) by ketones, aromatic and chlorinated hydrocarbons and diluted acids and bases
- Poor burning behavior
Recycling of PET
Polyethylene Terephthalate or PET products are 100% recyclable and is the most recycled plastic worldwide. PET can be easily identified by its recycling code #1.
As with virgin PET, recycled PET (rPET) can be used to make many new products, including polyester staple fibre/filament used for apparel (clothing), home textiles (duvets, pillows, carpeting), automotive parts (carpets, sound insulation, boot linings, seat covers) and industrial end-use items (geotextiles and roof insulation), and new PET packaging and bottles for both food and non-food products. It is generally blended in a ratio of virgin to recycled, depending on the application required.
To date, recycling PET bottles has saved over 1 million tonnes of carbon, avoided using almost 5 million m3 of landfill space and reduced resource consumption. Recycling plastic bottles decreases the need for raw materials and saves energy. Recycling a single tonne of plastic bottles saves 1.5 tonnes of carbon versus landfilling or incineration. (Credit: Worldwide Responsible Accredited Production – WRAP).
Low diffusion coefficient makes PET much more suitable than other plastic materials for use as a recovered, recycled material.
Post-consumer PET bottles are collected and processed through a series of special washing processes or by a chemical treatment to break down the PET into its raw materials or intermediates which are further used to produce recycled PET (rPET) flakes.
Further heat treatment of recycled PET flakes removes any volatiles making them safe and thus meeting the requirements to be safe for direct food contact.
Also, PET bottles and containers that find their way to the landfill pose no risk of harm or leaching. Since the polymer is inert, it is resistant to attack by micro-organisms, and won’t biologically degrade. PET bottles can also be easily crushed flat and hence, takes up relatively little landfill space.
In Closing
As per Petco, PET is widely recycled in South Africa – it has some of the highest recycling rates of any polymer, due to the sheer volume of products and packaging made from PET and its ease of processing. Over 74 300 tonnes of PET were recycled in South Africa during the last financial year and these rates have been steadily increasing for the past five years.
Plastics South Africa reports the input recycling rate for 2018 as 46,3% for all plastics.77 This is the ratio of plastics collected for recycling against the total plastic entering the waste stream
Closed-loop recycling means that a material can be recycled indefinitely without degradation of properties, using less raw materials and PET is material
Why do we produce plastic packages that are recyclable rather than biodegradable? The answer is simple: because in our view it makes better sense from both an environmental and economic perspective to capture the raw material and energy contained in plastic that can be used again and again, instead of losing it as it degrades. And of course because we have no data to confirm the full results of the biodegradability of these other products, we cannot with good conscience produce these.
At Dispak, as South Africa’s Largest Manufacturer and Distributor of PVC, Polyprop and PET sheeting and packaging, we develop various film and packaging solutions to meet whatever your need may be.
Everything we manufacture is 100% recyclable and we welcome drop off’s at our facility in Chamdor, Krugersdorp. With a reputation for stringent quality to exacting standards, we hold A BRC Global Standard for Packaging and Packaging Materials.
“All about Plastics – What is PET?”, 7 January 2021, https://www.plasticsinfo.co.za/2021/01/07/all-about-plastics-what-is-pet/
“Polyethylene Terephthalate (PET): A Comprehensive Review” https://omnexus.specialchem.com/selection-guide/polyethylene-terephthalate-pet-plastic
“How is PET Recycled”, https://petco.co.za/how-is-pet-recycled/
WWF Plastics report: 02 November 2020, https://wwfafrica.awsassets.panda.org/downloads/wwf_plastics_report_final_2nov2020.pdf