3D Printer Filament Types: Functional Filaments

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16 Jun, 2021

3D Printer Filament Types: Functional Filaments

Looking Beyond Common 3D Printing Filament Types

There are many 3D printer filament types that exist beyond the realm of common desktop filaments. In fact, there is a whole world of printable functional engineering plastics that can do a lot more than simply withstand moderate bending forces under mildly increased temperatures.

Maybe you’re interested in sending plastics into space or replacing metal components with polymers. Or maybe you need a conductive strong filament to print electronic components. Or how about a plastic that conducts heat rather than insulates?

If so, then good news. This article is going to take a look at some of these 3D printer filament types and introduce wondrous industrial-grade filaments. 

High Specific Strength Filaments

Most of the common filaments we looked at previously were fairly average in terms of the tensile strength of polymers, ranging from 30-50 MPa for ABS, and 60-65 MPa for unfilled PETG

PLA also falls broadly within that range. 

These consumer-grade filaments can be enhanced by the addition of fillers to increase the tensile strength, but adding a filler to an average plastic has diminishing returns considering the other high-end polymers available, which are stronger in their unfilled default state.

Such high-end, high-temp engineering polymers (such as PEI or PEEK, or PAEK) have higher molecular weights than the consumer level filaments, meaning they have higher melting points and higher densities. 

All being equal in terms of volume and geometry, parts printed with these advanced polymers tend to be heavier than parts printed with the basic filaments, yet the parts are significantly stronger per unit mass than common filaments. 

This means that less material can be used to achieve the same strength as the equivalent part made with a weaker material (ABS for example). With the reduction in materials, weight savings of up to 55% per part are not uncommon.

This is why a material’s specific strength (strength to weight ratio) is important, especially in aerospace. 

Research engineers in the domain of aerospace structures/materials (myself included) have been making use of these high strength/lightweight polymers in 3D printing for over a decade [1]. 

They have flown in space and are used extensively in civil aviation, particularly in aircraft interiors.

Here are a few commonly used high specific strength filaments used in aerospace with ABS and PLA for comparison. As you can see, the PEEK and Antero are clearly ahead here in terms of strength to weight.

Filament

Tensile Strength (MPa) 

Density (g/cc)


Specific Strength

(kN.m/kg)

PLA

48

1.26

38.1

ABS

32

1.05

30.5

ULTEM 9085

69

1.34

51.5

Z-PEEK

100

1.30

78.1

Antero 800NA 

90

1.28

70.31

Some of these plastics can even be plated using electroplating and electroless methods, but require some pretty specific changes to the surface chemistry of the parts, beyond what is achievable in the home printing enthusiast’s workshop. 

Regarding vapor smoothing, none of these plastics can be smoothed safely in the home as they require aggressive and potentially deadly chemicals.

ULTEM 9085, for example, can be smoothed (and strengthened) with the vapor but it requires the use of chloroform. Naturally, the use of a fume cabinet is advised when dealing with this stuff, lest you render yourself unconscious [2].

So why are these plastics so uncommon in the domain of consumer-level printing?

It’s largely due to the temperatures involved. The extrusion temperatures are in the region of 400-500 °C, which is not totally impossible on a desktop machine, but the real kicker comes from the chamber temperature requirements. 

Generally speaking, these types of filament can require chamber temperatures in the 200 °C regions (or higher) to produce fully annealed parts, which causes all kinds of headaches in terms of machine design and cooling. Not only that but the currents in the chamber must be managed properly as well, as even the slightest random cooler draft in the printer can result in warping and loss of layer adhesion which can result in build failure or diminished mechanical performance.

Another great feature of ULTEM 9085 is that it has a whole bunch of aerospace certifications for smoke, toxicity, flammability, and a whole lot more, which makes it attractive to aerospace manufacturing companies who don’t want to go through the expensive campaign of qualifying new materials/processes for use in aviation.

Currently, parts made from ULTEM 9085 can be found on the Airbus A350XWB aircraft, the International Space Station, and right here on my work table, as seen in the image below. The A350XWB features over 1000 additive manufactured parts made from ULTEM 9085 [3].

3D printed ULTEM cubeULTEM 9085 CubeSat (Image: Writer's own)

PEEK has been very popular in aerospace for years, even before its usage in additive manufacturing with many aircraft interior seals and panels being manufactured with the material.

In the early days of aerospace polymer printing, PEEK printing was mostly achieved with the SLS method, using a PEEK powder feedstock.

These days, PEEK is being produced in filament form too, and we are seeing more companies using PEEK printing in aerospace.

By simply swapping out the materials, engineers can reduce the weight of (non-critical) components by around 40% when compared to aluminum. By the use of generative design and topology optimization in combination with these plastics, the weight can be reduced even further.

How much further? That’s for another article perhaps.

High Stiffness Filaments

High stiffness plastics deserve their own section apart from high strength to weight ratio plastics like those in the previous section. ULTEM and PEEK in their natural unfilled form are strong, and they are stiff when printed as part of thick structures, but they are kinda bendy when printed in 2mm thick coupons.

In fact, there are commonly available filaments that outperform these aerospace parts in terms of their stiffness, that you can print on your desktop printer. They just won’t be very economical to send into space if you’re planning on building large components. 

You can see a comparison of the stiffness (Young’s Modulus) of various filaments in the table below. The higher the value for Young’s Modulus, the higher the stiffness of the part. We have included PLA for comparison against a common desktop filament.

Filament

Young’s Modulus (GPa)

Density (g/cc)

Specific Stiffness

(MN.m/kg)

PLA

3.03

1.26

2.4

ABS

2.4

1.05

2.3

ULTEM 9085

2.27

1.34

1.7

Antero 800 NA

3.48

1.28

2.7

Z-PEEK

3.72

1.3

2.9

FDM Nylon 12 CF

9.46

1.19

7.9

As you can see, the carbon-filled Nylon is really crushing it here.

The photo below shows a propeller printed in an early version of the Stratasys FDM Nylon 12 CF. This part was printed as part of a materials beta-testing program that I and some colleagues did while working with Stratasys Asia. The same design was printed in FDM Nylon 12 CF and also in ULTEM 9085.  Note the rough surface finish. This was during the early stages of the development of this specific material and the printing parameters were still being experimented with.

The chemistry of the plastic and the process were optimized for the production version of the material, resulting in better printing and an improved surface finish.

CF Nylon 12 drone propeller (Image: Writer's own)

The difference in stiffness of those materials at that thickness was significant. While ULTEM was strong in tensile strength, it deflected under loads to the point that it was useless in flight. 

The CF Nylon 12 was much stiffer and successfully achieved flight on the test drone. Stratasys claims that their FDM Nylon 12 CF material has the highest specific stiffness and the highest flexural strength of any FDM filament currently on the market. We have no reason to doubt that.

As you can see, the strongest plastic is not necessarily the stiffest, and vice versa, especially when you introduce filled plastics into the equation. 

This is why light/stiff filaments get a special category of their own in this article.

High-Temperature Filaments

ABS holds its strength at 100 degrees celsius, and even PLA needs a nozzle temperature close to 200 degrees to extrude, and so in a sense, all thermoplastic filaments are high temperature (from a human perspective). You wouldn’t want to accidentally grab a PLA nozzle while it’s cooling, speaking from experience.

But when we talk about high-temperature filaments, we are referring to materials that not only have a comparatively higher glass transition temperature (Tg) and resulting nozzle temperature, but also a higher heat deflection temperature (HDT) to go with it. These plastics have much longer polymers than your average off-the-shelf filaments and so require higher energy (more nozzle heat) to change phase and extrude. They can require temperatures over 400C to print at and often require advanced thermal management of the chamber environment. 

As we discussed in the previous article, these common desktop filaments’ HDT values max out at around 100 °C for ABS and about 60 °C for PETG. PLA is even lower.

That is, this is the maximum temperature that the test coupon can withstand without deflecting some specified distance (0.25mm) under some specified load (264 psi/ 1.8 MPa in this case).

In short, parts made from these high-temperature engineering plastics have a higher HDT and can maintain the integrity of the structure under higher temperatures.

The table below shows a variety of filaments and their HDT values. We have included ABS / PETG to show how they compare against high-temperature engineering plastics that are actually intended for high-temperature applications.

Filament

HDT  @ 264 psi / 1.8 MPa 

Glass Transition Temperature (°C)

Tensile Strength (MPa)

PLA

51

63

48

ABS

99.9

105.2

32

ULTEM 9085

153

186

69

Z-PEEK

160

143

100

ANTERO 800NA

147.23

155.81

90

Triboplastic Filaments

Triboplastics are tribologically optimized plastics designed for use as bearing surfaces and other components experiencing relative motion while being in contact with other components.

The word tribology derives from the Greek verb τρίβω, tribo, (to rub), so we are discussing plastics with low coefficients of friction. 

One of the main manufacturers of triboplastic filaments (or tribofilaments) is the German company Igus, which specializes in plastic bearings and other components for motion hardware and other machinery.

They have a long history of manufacturing molded/machined triboplastic parts and have now made some of these plastics available in filament form. The graph below shows the rate of wear of various common plastics in comparison to the iGlidur triboplastics from Igus.

iGlidur triboplastics rate of wear (Image: Igus)

These triboplastic materials work by a self-lubricating mechanism inherent in the polymer itself [4].

These filaments all require high nozzle and high build chamber temperatures, so you may struggle to print them on a consumer grade printer. 

Electrically Conductive Filament

Generally speaking, plastics are electrical insulators. They hold a charge and have high electrical resistance. 

To have a path to the ground, conductive fillers must be added to the material in order to lower the surface resistivity and allow the charge to flow. Typically some form of carbon is added to the feedstock by the filament manufacturer to vary the surface resistivity and by extension, the electrical conductivity of the material.

The surface resistivity of a material itself determines the rate at which electrical charge flows through (or over) an object, be it plastic, metal, or miscellaneous.

Materials with a low surface resistivity (typically below 1 x 10 5 Ω/ sq) are considered to be electrically conductive. 

Materials with higher values of surface resistivity in the range of 1 x 10 5 Ω/ sq to 1 x10 11 Ω/ sq. are considered to be electrostatic-discharge safe materials (or “ESD safe” materials for short) [5]. Anything higher than that, and you’re looking at an insulator. Most plastic filaments that are not intentionally engineered to have specific electrical properties fall into this category. 

Electrically conductive filaments are widely available and come in a range of common polymer flavors including PLA, ABS, PETG. 

On the higher end of the filament market, there are conductive versions of PEEK commercially available such as PEEK ELS CF 30, which contains carbon fiber. 

There are other conductive PEEK filaments in the research stage and utilize graphite nanoplates and carbon nanotubes. Suffice to say, conductive filaments with high specific strength are widely desirable in aerospace (satellites especially). The image below shows the conductive PEEK currently under research by the European Space Agency [6] and their partners.

Conductive space PEEK...conducting! (Image: Piep)

ESD Safe Filament

As mentioned in the previous section, a material with surface resistivity in the range of 1 x 10 5 Ω/ sq to 1 x10 11 Ω/ sq. is considered to be an electrostatic discharge (ESD) safe material. This means that they slow the charge down as it passes through the body of the object, which makes these filaments suitable for applications requiring ESD protection [7].

ESD safe filaments are used in electronics manufacturing/testing, especially for jigs, fixtures, and enclosures designed to protect electronics from accidental ESD damage.

When an arc occurs in an ESD safe material, it does so at a slower velocity, and with lower energy, as it tries to the ground. High energy arcs destroy electrical components, as you can see in the image below. 


ESD sparks over RF electronics componentsESD sparks over RF components

 ESD safe materials are all about reducing that energy so it can dissipate without damaging anything. You don’t want the resistivity too high though, lest your filament becomes an insulator. Insulators store charge. ESD safe materials let the charge out gradually. Conductors let it pass through quickly.

Once more, the material properties are altered by the addition of carbon in some form, and so there is a range of ESD safe materials available for all budgets ranging from ESD safe PLA filaments through to static-dissipative high-temp engineering plastic filaments such as VICTREX PEEK ESD101.

Thermally Conductive Filament

Plastics are generally good thermal insulators (if they don’t melt) and many high-temperature engineering plastics are used for exactly that purpose.

Compared to metals, however, they are pretty terrible at conducting heat.

There are thermally conducting filaments available, however, which are suitable for the printing of all manner of heat-management-related tasks such as heat sinks and radiators. 


Heat sink printed with TCPoly Ice9 filamentPrinted plastic heatsink. (Image: TCPoly)

The heat sink seen in the above photo was printed with plastic from the TCPoly Ice9 range of filaments. TCPoly claims to have the filament with the highest thermal conductivity of any plastic in the world. They come in a range of polymer types including PETG, TPU, and Nylon.

Let the buyer beware, however. While these commercially available thermally conductive filaments can be 50 times more thermally conductive than traditional plastics, they are still 10 times less thermally conductive than metals at the time of writing this article.

It is still early days for thermally conducting filaments, and they do seem to be best suited for a fairly narrow range of specialized applications. As the value of these applications becomes more apparent, we will likely see more filaments available with even higher levels of thermal conductivity. There is ongoing research that is yielding conductivity levels in polymers exceeding those of pure metals [8].

Because these filaments can be printed on a slightly modified desktop printer, it means that custom thermal management solutions can be printed very easily compared to the traditional route of manufacturing for such items (machining).

When combined with topology optimization and generative design, thermally conductive feedstocks could yield some very interesting designs indeed.

Summary

As we have seen, there are functional filaments available to suit every budget, be it for the consumer-level printer or an industrial-grade printer.

Naturally, there are a lot of consumer-level filaments available with enhanced electrical properties because frankly, it’s not that difficult for manufacturers to mix a pile of carbon dust up into a vat of molten thermoplastic. 

The higher-end engineering plastics, however, are more costly and offer enhancements not just to the mechanical and thermal properties, but many also offer superior chemical resistance, FST ratings, aerospace certifications, low outgassing, and a whole lot more.

And this is why there is such a huge price difference between a consumer-level functional filament and a high-end functional filament. 

Development and testing are not cheap, and certification takes a lot of time and money.

So while these advanced high-temp engineering plastics are typically beyond the reach of the average consumer due to the high cost of machinery and the plastics themselves, there are still plenty of interesting plastic filaments around for those wishing to experiment with their desktop printers.

With the slightest modifications to a $300 printer, anyone can now print electrically or thermally conductive items with ease and with a range of acceptable strengths and stiffnesses for more Earth-based applications.

References 

[1] Keane, P., Chua, C. and Joshi, S., 2016. Embedding Electronics In Printing ULTEM 9085 Quadcopter. In: International Conference on Progress in Additive Manufacturing (Pro-AM 2016). Singapore: Research Publishing, pp.79-84.

[2] Fischer, M. and Schöppner, V., 2016. Fatigue Behavior of FDM Parts Manufactured with Ultem 9085. JOM: the journal of the Minerals, Metals & Materials Society, 69(3), pp.563–568.

[3] Stratasys, 2020. Stratasys to Produce 3D Printed Flight Parts for its A350 XWB Aircraft. [online] Stratasys. Available at: <https://www.stratasys.com/explore/blog/2015/airbus-3d-printing> [Accessed 11 June 2021].

[4] Igus, 2020. Self-lubricating Plastics. [online] Igus.com. Available at: <https://www.igus.com/info/self-lubricating-plastics> [Accessed 11 June 2021].

[5] Keane, P., 2020. Electrically Conductive Polymer Composites for 3D Printing - 3D Printing. [online] 3DPrinting.com. Available at: <https://3dprinting.com/3d-printing-use-cases/conductive-materials-for-3d-printing/> [Accessed 11 June 2021].

[6] ESA, 2020. Testing 3D-printed plastic electrical component. [online] Esa.int. Available at: <http://www.esa.int/ESA_Multimedia/Images/2020/11/Testing_3D-printed_plastic_electrical_component> [Accessed 11 June 2021].

[7] Keane, P., 2020. ESD Safe Materials for 3D Printing - 3D Printing. [online] 3DPrinting.com. Available at: <https://3dprinting.com/3d-printing-use-cases/ESD safe-materials-for-3d-printing/> [Accessed 11 June 2021].

[8] S. Shen, A. Henry, J. Tong, R. Zheng and G. Chen, "Polyethylene nanofibres with very high thermal conductivities", Nature Nanotechnology, no. 5, pp. 251–255, 2010. [Accessed 11 June 2021].

More by Phillip Keane

Phillip is an aerospace/manufacturing engineer, writer and university lecturer from the UK specializing in 3D printing for aerospace applications, CAD, topology optimization and project management. He did a BEng in aerospace engineering at Coventry University in the UK, an MSc in Space Studies at I...

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