APP – Mixing materials

The Filament Maker gives you the option to blend different materials together.

Options are countless ; you can create a material which really corresponds to your needs.

But not all blends will work perfectly or straight away. Working with additives can be “dangerous” for the machine, unless you follow a safe methodology.

1. What can you mix ?

First you must choose a base polymer. Obviously, it is impossible to extrude additives only, without a carrier material. Then, in theory, you can mix in any number of additives and other polymers, as long as they are compatible.

That includes:

  • polymers
  • “structural” additives (like carbon fiber)
  • “functional” additives (like carbon nanotubes)
  • “aesthetic” additives (like colorants)
  • chemical additives (like chain extenders)

2. How do I know two materials are compatible ?

Compatibility is hard to quantify. Here are a few basic rules:

  • polymers must have an overlap in the their processing windows
  • polymers must have a similar viscosity
  • all particles must be smaller than 4mm
  • all substances should have a similar shape (if possible): metal powder will work better with plastic powder than plastic pellets
  • additives which do not melt should be smaller than the 3D printer’s nozzle (often 0.4mm). In practice, an even smaller size is recommended (100 microns or less)

In most cases, the only way to be sure is to start experimenting, safely and methodically.

3. Where to start ?

There are two main difficulties when mixing different materials into filament:

  • Mixing. This means making the blend homogeneous
  • Controling the flow. This is crucial in order to obtain a good quality, consistent filament.

You can either achieve that in two steps or just one :

  • Pre-compounding the additives/plastics together. That is typically done with a twin-screw extruder, which mixes very well all kinds of compatibles materials into pellets. Then you can feed those pre-mixed pellets in the Filament Maker.
  • Skipping the pre-compounding step, and therefore combining the mixing and filament making processes at the same time with the Filament Maker. In that case, you can “manually” shake all the materials in a jar, and feed the blend directly in the hopper of the extruder. In general, you will be limited as to how much additive you can add. Having a good shape/size/composition/behavior compatibility is especially important here.

In a nutshell, dissociating the compounding and filament making steps, will allow you to work with more difficult blends (bigger percentage of additive, several plastics together…).

4. How much additive can I add ?

Because it can be very easy to clog the Filament Maker with additives or incompatibles blends of polymers, here is how to proceed carefully:

  • You should first experiment with the unmixed, unblended, base material (the carrier polymer). The goal is to see if the flow of carrier can be controled to achieve a good diameter tolerance. Most of the parameter finetuning can be done with the carrier only.
  • Then start with a small percentage of additive or added polymer, like 5% (weight). In such small quantities, the risk of clogging the equipment is low, and that already allows you to see how well the additive can be dispersed.
  • Then, if the first steps are successful, you can gradually increase the percentage of additive, 5% by 5%. If you skipped th pre-compounding step, there will be a critical amount of additive, beyond which the machine can become fully clogged. By keeping an eye on the motor current value in the datalog, and making small adjustments, you might be able to see it coming.