3D Printing Tutorial – Introduction (EN)

C3 – Thermoplastics – Filaments

In this third chapter we’ll introduce the materials that are commonly used with FFF 3D printers. We will present the thermoplastics and their main properties.

As mentioned in the introduction, thermoplastics are the materials used in 3D printing (FFF). You already know that thermoplastics can be heated (melted) and shaped.

When we talk about 3D printing and say “filament,” we’re referring to the thermoplastic thread that is sold on a spool. There are several thermoplastics, which means there are also several types of filament.

The most common filament types in FFF are:

• PLA – Polylactic acid – made from corn, or sugarcane for example, also used for bags or some containers.
• PETG – Polyethylene terephthalate glycol – similar to PET used for water and soda bottles.
• ABS – Acrylonitrile butadiene styrene – widely used in toys, phones, and automotive parts fabrication.
• Nylon – there are several varieties of this thermoplastic – used for clothing, carpets, and various other parts.

 

We’ll focus mainly on PLA. Why?

All the above listed materials are thermoplastics – we can heat them and work with them. However, the temperature at which we can work with them depends on the specific plastic. For example, to shape PETG you need to heat the plastic to about 230° C. To shape PLA, heating it to roughly 180 °C is sufficient. This means that when using PLA you can use a less powerful heater – you can save some energy. There are additional reasons to prefer PLA: it’s easier to work with, easier to find in the market, and is generally cheaper.

With time, after getting some experience from working with these materials, you’ll understand much more easily what we’re trying to explain. Below you can find a table showing two characteristic temperatures for these four thermoplastics – the glass-transition temperature and the melting temperature:

WP DataTables

But what exactly are the glass-transition temperature and the melting temperature?

You’re probably left a bit confused about what these temperatures mean, right?

The glass-transition temperature is the temperature at which the plastic starts to become soft and can deform. Later, when you start working directly with the printer you’ll understand this better.

You may have already seen one of your toys take on a strange shape after being left in the hot sun – or even inside a car? What happened? The toy warmed up until it reached its glass-transition temperature and became deformed. When it cooled down, it kept that odd deformed shape.

The melting temperature is the temperature at which the plastic completely loses its shape and becomes viscous, almost like honey. At this temperature the plastic is much easier to shape. When we start using the printer, this will be the temperature we have to heat the filament to in order to print.

Notice that the melting temperature is always higher than the glass transition temperature.

 

Different filaments, different characteristics…different uses?

Well spotted! In general, all filaments can print roughly the same kinds of objects. However, after looking at the temperature table above we can think more carefully about the function of the object we want to print and which material best fulfills that function. Sounds complicated? Not at all…

Consider a toy that has a motor. Some toys have motors that move arms or wheels, for example. Motors tend to warm up slightly when they’re in use. Imagine we’ll be using this toy on a summer day in the sun. The motor heats up when turned on, and it could get even hotter on a hot summer day. Therefore the toy must be built from a thermoplastic that can withstand a temperature rise without deforming. Looking at the temperature chart, we can immediately rule out some thermoplastics. Which ones? PLA and nylon, because their glass-transition temperatures are around 60° C. This toy needs a higher glass-transition temperature. PETG has a higher glass-transition temperature, but it may still be too low for the intended use. In this case, ABS would be more suitable.

There are many other properties that could be discussed, and we’ll cover some of them over time. For now, we will only present a table that introduces additional properties of these materials:

WP DataTables

 

Finally, we’ll introduce another example in order to illustrate some of these properties.
Imagine we want to print a cup for drinking water:

• The glass needs to be adequate to ‘hold’ the water inside – it should not be an absorbent material.
• The glass needs to be made of a non-toxic material – it must be safe to keep water if we want to drink it.

In this case, what would be the best filament to print the cup?

 

Let’s recap:

Thermoplastic – plastic that when heated can be shaped, and when cooling can hold a shape.

PLA – a thermoplastic that is easy to use and easy access on the market.

Glass-Transition Temperature – temperature at which the plastic starts to deform.

Melting Temperature – temperature at which the plastic loses shape and becomes viscous.

In summary:

There are various types of thermoplastics. Each with its own glass-transition, and melting, temperatures.
We’ll work mostly with PLA because it is easy to work with and it is easy to find in the market.

The presented concepts will be quite useful during the work with the 3D printer! If you managed to understand them, you will be able to realize why it is necessary to define specific temperatures for each filament we use with the printer.

So, understanding the different characteristics of thermoplastics allows a person to make a smarter choice about the best material that is required to print a certain object.

Finally, we’re sure that you do not even realize this but….do you know that in this chapter you’ve learned concepts in the field of Materials Science?

* * * Want to test what you’ve learned about Thermoplastics? * * *
* * * Solve a small quiz. Here!* * *

Ready for the next chapter? Do you have any doubts or questions to ask? Great!
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Don’t forget… HAVE FUN!