Making filament by mixing several thermoplastics is possible, but only under specific conditions.
In this article, it is assumed you wish to blend two polymers named A and B.
Please note that this article only covers the blending of several polymers. Inert additives are a completely different matter, since they don't need to melt inside the barrel.
1. Each individual polymer must be processable on its own
Extruding good quality filament can already be difficult when working with a single unmixed polymer.
Please find our extensive guide on the matter. Selecting the right material is really crucial - not all materials can be turned into good filament.
2. The different polymers must be compatible with one another
Even though you can produce good quality filament out of A and B individually, perhaps they won't react well when mixed together.
Though it is hard to give exact numbers, here is a set of 'rules of thumb' to keep in mind. In order to be compatible, A and B should have :
- a similar particle size
- a similar density
- overlapping melting ranges (obviously, you wouldn't be able to properly melt PLA and PEEK at the same time)
- a similar viscosity
As always, we advise you to start small, and break the project into steps.
Step 1: Process A on its own. Really take the time to experiment its processing window, try different temperatures. Again, please feel free to follow our extensive guide.
Step 2: Same for B.
Step 3: If there seems to be a thermal overlap at which both A and B can be processed reasonably well, then pick the easiest of the two, and go for a 90/10 mix.
Step 4: While adjusting the settings slightly, if needed, test different A/B ratios.
4. Special method: precompounding
The easiest route to work with polymer blends is to purchase pre-compounded pellets. This means that the pellet supplier has already done the mixing work for you, and that the blended pellets can be treated as just one normal thermoplastic. You might even have access to processing recommendations on it Technical Datasheet.