Polyethylene terephthalate glycol, known as PETG or PET-G, is a thermoplastic polyester that delivers significant chemical resistance, durability, and formability for manufacturing. PETG is an adaptation of PET (Polyethylene terephthalate) where the ‘G’ stands for glycol, which is added at a molecular level to offer different chemical properties. PET uses the same monomers as the glycol modified PETG, but PETG has greater strength and durability, as well as being more impact resistant and better suited to higher temperatures.
Due to the low forming temperatures of polyethylene terephthalate glycol it is easily vacuum and pressure formed or heat bent, making it popular for a variety of consumer and commercial applications. These properties also make one of the more widely used materials for 3D printing and other heat-forming processes. PETG is also well suited for techniques including bending, die cutting and routing.
How is it Made?
In order to understand how polyethylene terephthalate glycol is made, it is important to first understand how PET was discovered and created.
Advances in polymer chemistry in the mid-20th Century saw scientists discover new materials that could be used instead of traditional organic products. Phthalic acid polymers were in use in paints and varnishes, while glycol-based synthetic fibres were being used in textiles. However, the phthalic acid products were too soft to be used as fibres and the glycol-based materials had melting points too low to allow for their use in textiles.
British scientists, John Whinfield and James Dickson combined these substances in 1941 to create polyethylene terephthalate (PET). Using the process of esterification to heat glycols with terephthalic acid, they created long-chain molecules of PET that could be turned into fibres with high melting points low dissolvability. PET became widely used in textiles by 1946 and by 1952 PET was being used as film for food packaging. In 1976, PET was used for the manufacture of rigid bottles that could manage carbonated soft drinks, beer and mineral waters. Despite being one of the most widely used plastics today, PET does have some disadvantages, including being susceptible to crystallisation at high temperatures. This turns the PET opaque and weakens its structure.
The creation of polyethylene terephthalate glycol-modified, or PETG, replaced the ethylene glycol in the molecular chain with a larger monomer, cyclohexane dimethanol, which stopped the crystallisation associated with PET. With improved heat resistance, PETG molecules do not collect together as easily as with PET, which lowers the melting point and inhibits crystallisation.
This means that polyethylene terephthalate glycol can be used for thermoforming, 3D printing and other higher temperature applications without losing its properties.
What is it Used For?
PETG has applications in a range of industries due to being resistant to heat, impact and solvents. It is widely used for packaging (both retail and medical), advertising displays and electronic insulators.
It is also widely used in 3D printing since the glycol prevents the problems associated with PET, such as overheating and becoming cloudy and fragile. It is also possible to sterilise PETG items. With good adhesion between layers, minimal deformation during printing, good resistance in low temperature environments, chemical resistance against bases and acids, and an absence of odour while printing, PETG is becoming the favoured material for 3D printing.
polyethylene terephthalate glycol is ideal for producing parts that are flexible with a good resistance to shock, such as pressure-clad items, protective parts or food containers.
Is it Environmentally Friendly?
PETG can take decades to break down completely when sent to landfill, but it is easily recycled using chemicals to break the polymer chains back down to their original components. These components can then be used as raw materials for the manufacture of new polymers.
Producing fresh plastics uses a large amount of energy and water, so recycling plastics back into production greatly reduces the consumption of natural resources. Recycling also prevents PETG products from breaking down into microscopic fragments that pollute the oceans and the world’s water supply, threatening aquatic life.
So, while polyethylene terephthalate glycol, like all plastics, can be harmful to the environment, it’s recyclability can greatly reduce or remove this negative impact.
Properties
As a copolymer, PETG combines the properties of PET and glycol. This combination means that the overheating issues associated with PET are reduced.
The main properties of polyethylene terephthalate glycol include hardness, chemical and impact resistance, transparency and ductility. An easily extruded material with good thermal stability, PETG is particularly compatible with food uses. polyethylene terephthalate glycol is particularly good for 3D printing, having an extrusion temperature of between 220° and 260°C, with a print speed of 40-60mm/s.
However, for all of the positive properties, PETG requires the use of a heating plate to avoid the warping found with ABS 3D printing and is more prone to scratches than PLA. It is recommended that a heating tray does not exceed a temperature of 80°C. The sticky appearance of PETG also means that printing supports can be difficult to remove.
PETG can quickly take in moisture and will keep better in a cool and dry environment.
Advantages
polyethylene terephthalate glycol offers a number of advantages over other substances, including acrylic and polycarbonate. These advantages include:
1. Strong and Cost-Effective
PETG’s strength and impact resistance means it is ideal for glazing and high-strength display units. It is also ideal for 3D printing products, displays and signage.
2. Food-Safe and Recyclable
PETG is safe for use for food containers and bottles for drinks. It is also fully recyclable, which reduces waste and the potential negative environmental impact.
3. Easily Formable
PETG is both vaccum and thermo formable and can withstand high pressures without cracking. It can be injection moulded into a variety of shapes or extruded into sheets.
4. Easily Coloured
PETG is naturally transparent, which allows for unique effects, but it can also easily be coloured and blended to create different appearances.
5. Non-Toxic and Odourless Emissions
PETG is non-toxic and odourless during 3D printing, making it perfect for both home and office use.
Disadvantages
There are very few disadvantages associated with using polyethylene terephthalate glycol, but care still needs to be taken, particularly with the temperature parameters.
1. Parameters need to be Followed
When 3D printing PETG, it is advised that the correct temperature parameters are used. It is advised that you follow the parameters set down by each material manufacturer, usually 210-260 ºC extruder and 60-80 ºC base, although a cold base can also be used. A low printing speed is also recommended (30 – 35 mm/s) while the optimal values for the 3D printer are achieved.
2. Prone to Oozing
PETG is more prone to oozing than either PLA or ABS, which means that you will need to experiment with bridging and retraction settings during 3D printing. As a result, there may also be a requirement for more post-processing to remove any blemishes.
3. Brittle if not Stored Correctly
PETG will absorb water if not stored in a dry environment, which will make parts more brittle.
4. Environmental Issues
As with all plastics, PETG has a potentially negative environmental impact if not disposed of properly. It can take decades to decompose and lead to micro-plastics being fed into the world’s oceans. However, PETG is readily recyclable, which removes these environmental problems.
Production Methods
PETG is produced using a two-step, melt-phase polycondensation process. This relatively simple process joins two different monomers together, accompanied with the release of a small molecule such as water.
PETG can be injection moulded, sheet extruded or extruded as a filament for 3D printing. This clear, amorphous thermoplastic can also be coloured during processing.
Applications
The properties of polyethylene terephthalate glycol make it suitable for a wide range of different applications, including:
1. Food and Drink Containers
Because it has good chemical resistance and is easy to thermoform, PETG is widely used for items such as cooking oil containers, drinking bottles and FDA-compliant food storage containers. It is also used for cosmetics packaging and the light weight and high strength delivers advantages for distribution costs and effectiveness.
2. Medical and Pharmaceutical Applications
The rigid structure of PETG means that it can survive harsh sterilisation processes, which makes it an ideal substance for medical implants as well as packaging for pharmaceutical and medical devices.
3. Retail Stands and Displays
polyethylene terephthalate glycol is widely used for point-of-sale retail stands and displays. Since it can be coloured, it is also ideal for signage.
4. Machine Guards
PETG is also used to manufacture machine guards. The clear plastic is easy to form while also offering protection for users. PETG guards are often used in food processing as they are easier to form than polycarbonate and more durable than acrylic.
5. 3D Printing
As mentioned above, PETG has gained popularity for use in modern 3D printers. A polyethylene terephthalate glycol filament prints easily and provides excellent layer adhesion. Low shrinkage rates allow for larger prints than with PLA or ABS, while PETG is also strong, chemical resistant and odourless while printing. It is advised that a cooling fan is used while printing with PETG, while problems with printing bed adhesion can be overcome by putting down a layer on the build plate.
Future of PTEG
The future of polyethylene terephthalate glycol looks bright as the global market continues to increase, although there is an ongoing need to ensure used PETG materials are recycled.
Conclusion
polyethylene terephthalate glycol is a well-used and versatile plastic with many properties that are better than those of comparable materials. With an increasing uptake in 3D printing applications, PETG is also widely used in the food and medical industries.
Source: https://www.twi-global.com/technical-knowledge/faqs/what-is-petg