Carbon Fiber 3D Printing, Part Four: Matrix Materials

In parts one, two and three of this series, we’ve discussed the variety of technological developments taking place in the 3D printing of composites but have not yet covered the materials used. Well, except for carbon fiber.

The matrix materials used with carbon fiber can be just as important as the reinforcement material itself. In this section, we will explore the matrix polymers used so far in carbon fiber 3D printing. We’ll also take a look at some other reinforcement materials used instead of carbon fiber.

Chopped Fiber-Filled Filaments

Outside of additive manufacturing (AM), the range of matrix polymers that can be reinforced with fiber materials stretches the gamut, including many epoxy, polyester, nylon and vinyl formulations. In 3D printing, however, each new material that is developed is processed based on the parameters of a given AM technology.

For 3D printing filaments filled with chopped carbon fibers, there is a broad mix of matrix materials in use, from ABS and PLA to Polycarbonate and PEEK. In fact, there are just about as many carbon fiber composite filament types as there are thermoplastic types in FFF 3D printing.

Outside of chopped carbon fiber-filled filaments, however, the matrix materials are much more limited. And, while more are being developed, the two predominant matrix polymers in use by continuous reinforcement 3D printing companies are nylon and variations of PAEK.

Nylon (Polyamide)

Many of the interesting startups focused on continuous carbon fiber 3D printing technologies use either nylon 6 or nylon 12 as a matrix material. The first commercially successful synthetic polymer, nylon is a silky, flexible material derived from crude oil. After being used for bristles in toothbrushes, the plastic became widespread when it was used for making parachutes, body armor, ropes and helmet liners during World War Two.

Scanning electron microscope image of a nylon fibre. Image courtesy of CSIRO.

Nylon is known for its impact, abrasion and chemical resistance, as well as its flexibility, durability and dimensional stability. It is also hygroscopic, meaning that it readily absorbs moisture, which can negatively impact the aforementioned properties.

In AM and elsewhere, you may come across different variations of nylon, including 6/6, 6, 6/12, 11 and 12. So far, in carbon fiber 3D printing, only 6 and 12 are commercially available. Nylon 6 has hardness, tensile strength, and abrasion resistance similar to nylon 12. Nylon 12 has lower moisture absorption, good chemical resistance and can accept high loading of filler materials. Nylon 12 also has the lowest melting point of the varieties discussed.

The PAEK Family

The polyaryletherketone (PAEK) family of semi-crystalline polymers sort of represents the gold standard of plastics in 3D printing. These family members must have good genes because they all exhibit high mechanical strength, temperature and chemical resistance, and low flammability. The materials in this group also demonstrate high dielectric strength and thermal conductivity.

A CNC fixture 3D printed with PEEK reinforced with carbon fiber. Image courtesy of Desktop Metal.

You’ll learn from third wave desktop 3D printer manufacturers that extremely high extrusion temperatures are necessary to print with PAEK plastics and that an enclosed, heated chamber is necessary to maintain proper interlayer adhesion.

Companies that offer reinforcement 3D printing with PAEK polymers are focused on PEEK and PEKK. However, it’s worth mentioning their lower-cost cousin polyetherimide (PEI), better known by the brand name ULTEM, simply because it is an important polymer in AM overall.

Whereas PEKK possesses all of the same properties as PEEK mentioned above, PEKK can exhibit greater compression strength and also has a much wider of processing parameters than its extra-ether-inclined sibling. It can be printed at a lower temperature than PEEK with better layer adhesion. PEI is weaker and less temperature resistant than its cousin but is more affordable.

Though PEI is not yet offered by a composite 3D printing company, it’s not unlikely that it will be, given its lower price and the fact that it already has aerospace standards associated with it, thanks to its wide implementation by Stratasys.

Carbon Fiber Alternatives

Basalt fibers. Image courtesy of Technobasalt.

Fiberglass: Fiberglass is a low-cost alternative to carbon fiber. Though not as stiff, it is stiffer than a plastic material on its own and demonstrates high electrical insulating properties and good heat resistance.

Basalt: Born from volcanic rock, basalt is comparable to fiberglass in terms of cost, but is stronger than the most common type of fiberglass, E-glass.

Aramid: Though more expensive than the other reinforcement fibers discussed in this series, Aramid (which may be more familiar by the brand name Kevlar) is less dense and therefore lighter than the other materials.

Ceramics: Ceramics can demonstrate high strength, stiffness, temperature stability and durability.

There are always new materials in development and some of the companies we’ve mentioned in our series have previously discussed some of the materials they’re exploring. So, we’ll certainly see this list expand. In the next section of our series, we will look at the applications of fiber reinforcement 3D printing.

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