Understanding the Characteristics and Applications of Different 3D Printing Materials

Part 1: PLA and PETG

By Mitch, July 2024

In this, the first of a series of articles about different materials, I’ll explore the makeup of both PLA and PETG along with along with their good and bad points. Let’s first then start with PLA.

PLA (Polylactic Acid) is the most commonly used type of filament material in the world of FDM 3D printing.

So, what makes PLA such a popular and useful 3D printing material?

PLA - The Basics

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We've established that PLA is commonly used in 3D printing and has a variety of uses. But why is this? In simple terms, PLA is easy to use and work with, it's easy to produce and has good dimensional accuracy. PLA is the go-to material for most new users and old hands alike for these exact same reasons and the range of colors and different types within the PLA genre is extensive.

Standard PLA is the most common, but you can also find PLA+, silk, matt, rainbow, glow-in -the-dark and even colour changing PLA to name but a few. There are also variants of PLA where a particular additive has been included which changes the consistency and performance of standard PLA.

I've talked about the how PLA is easy to work with and this is partly due to its low melting point or GTT (Glass Transition Temperature) *. To become workable for 3D printing, you need a nozzle temperature of between 190-220ºC and a hot bed temperature of around 50-60ºC. This is pretty much the standard for entry level FDM printers which is why PLA is used so much in that realm.

The other aspect of PLA which is sometimes overlooked is that it is entirely made from natural, renewable sources such as corn starch or sugar cane. This makes PLA fully biodegradable under the right conditions which, with today's issues of waste and climate change, can only be a good thing.

PLA though does have both good points and things that could cause issues so let's now look then at these Pros and Cons as we commonly know them.

Pros

• Easy to work with: Low printing temperatures and easy to cut and sand in post processing

• Rigid and relatively strong: Can withstand a certain degree of impact

• Good dimensional accuracy**: Good quality PLA will be +/- 0.02mm or better

• Long shelf life: If stored correctly: PLA will last as long as you need it

Cons

• Low heat resistance: The low working temperature has a disadvantage when it comes to heat exposure when printed

• Blockages occur regularly: The low melting point again plays a part at slow printing speeds

• Requires cooling fans: Somewhere between a pro and con for this as most printers have fans anyway

• Filament can get brittle and break: If not stored correctly, the filament will harden and break. Vacuum storage is suggested and/or the use of a filament dryer

• Not suitable for outdoor use: PLA is vulnerable to water and UV light so won’t react well to being outdoors

PETG – A different choice

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PETG (Polyethylene Terephthalate Glycol) is a durable, hard-wearing polyester combination that can be used as a filament in FDM 3D printing.

Now, here’s the science part!

PET was first formulated in 1941 by the British scientists Dickson and Whinfield who patented their product for the manufacture of fibres. These fibres were intended to replace cotton as a source material for uses in textile manufacturing. It did however take until 1946 for PETG to be settled into the industry but it is still widely used today.

By 1952 use of PET had expanded into food packaging in the form of transparent film and then in 1976 in the use of rigid drinks bottles. Drinks with low oxygen sensitivity were particularly best suited such as carbonated soft drinks, mineral water, and beer. The significance of this can’t be understated as it made PET the most used plastic in the world.

PETG itself is a copolymerisation of the original PET. The addition of ethylene glycol (the “G”) made the PET less prone to crystallization and reduced its melting point. It also had a better thermal stability allowing it to be used to create flexible extruded parts as made by FDM 3D printers.

Why choose PETG Filament for 3D printing?

As a printing material PETG has excellent flexibility, durability, and chemical resistance. This makes it an ideal choice for 3D printing enthusiasts who may want to try more than just model making.

That being said, it is still a good choice for those modellers who need good impact resistance and additional strength in their creations. It’s also great for models requiring snap together or movable parts.

The use of PETG filament in 3D printing is much the same as that of PLA (Polylactic Acid); particularly if you are mainly interested in producing models for display etc. However, due to the properties of PETG mentioned previously, it is ideal for producing usable parts for machinery, medical devices, food containers and drinks receptacles.

The most common uses of PETG for the hobbyist 3D printing enthusiast could include:

• Cups – PETG is water resistant

• Lunch boxes – heat resistance can help prevent wilted sandwiches!

• Key fobs – good strength properties are ideal for an everyday item

• Outdoor plant pots – temperature resistance and water resistance combined

• Small handheld tools – pliers or handles for saws can be ideally suited

• Moving parts for models – snap together parts or those needed for items such as RC cars etc.

The uses in prototyping are also plain to see as the above items show the durability of PETG and its strength as a printing material.

How do I choose PETG filament?

When deciding to buy or use anything, it’s always worth taking a look at the Pros and Cons. In the case of PETG that’s no different and there are a lot of things to consider before you decide if PETG is the right choice for your project.

Let's then take a brief look at both sides of the coin.

PROS

• Strength and resistance to impact

• Flexibility

• Thermal resistance

• Good adhesion between layers

• Food grade - Check the laws and regulations regarding this in your country or region

• Minimal deformation when printing

CONS

• Can cause greater wear and tear to printer parts

• Higher printing temperatures

• Possible “stringing” issues when printing

• Can stick “too well” to build plates

• Can become brittle

• Scratches more easily

How to conserve PETG filament

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With any product you might purchase external factors are going to play a part in affecting the state of the filament. Therefore, you’re going to want to know how long it will last. Now for most people who are enthusiastic about 3D printing, a spool of filament might not last longer than 24 hours before it’s been used up! However, in this case, we’re not talking how much you use and how quickly but more about how long the integrity and quality of your PETG will remain intact.

Once you’ve purchased a roll of PETG it will have a natural shelf life of about 2 years under normal conditions. Atmospheric conditions and how well you store the filament will have an impact on that time span so keeping it stored correctly will be to your benefit. Damp, humidity or exposure to UV light and heat will have an effect on the quality of the PETG and in turn, the quality of your prints. Apart from trying to ensure your print workshop keeps the perfect environmental conditions, there are a few options available to you in terms of storage which will help you to avoid these external factors.

• Filament Drying Box: There are many of these on the market of varying types and cost and are basically electrical devices designed to dry and avoid humidity issues which may affect your filament. You could also make your own drying box and there are a few YouTube tutorials online to show you how.

• Vacuum Storage Bag: These are basically small, sealed bags specifically designed to fit a roll of filament and then use a vacuum pump to extract all the air. A small bag of desiccant is also added to help with damp.

Both of these options will of course be useful for all types of 3D printing filament.

And finally…

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PLA is a versatile and easy to use 3D printing filament which lends itself perfectly to creating models and prototypes. There are some issues that can occur while printing which can make quality and consistency a problem but overall, PLA is the perfect choice for display or demonstration items as long as they're used indoors and don't need to be subjected to any force or stress.

As an alternative to PLA, PETG is definitely worth a go especially if you’re wanting to print hard wearing and weather resistant items. The settings on your printer may take some time to perfect and there’s definitely a bit more wear and tear on the nozzle etc. but all in all PETG filament is a good choice for any 3D printing enthusiast.

As you might expect, Creality produce an extensive range of PLA and PETG filaments which can be bought direct from Creality.com. Check out the site for the best prices on everything you need to get started with 3D printing.

*See my previous posts about GTT as it refers to the workable temperature of the material rather than the more commonly referred to “melting point”

**Dimensional accuracy refers to the possible variation in diameter throughout a spool of PLA. The most commonly used diameter is 1.75mm so a dimensional accuracy of +/- 0.02mm means that some parts of the filament may be between 1.73 and 1.77mm)

 3D Printing Materials Part 2