The previous video was about technical ceramics and where they save money. This time we look at the plastics side – and at a possibility that only arises because we process pellets rather than filament: we can blend something in during printing and thereby change the end product.
Why this only works with pellets
A filament is finished. It was compounded, coloured and extruded to diameter at the manufacturer – nothing about its composition changes after that. Whoever prints chooses from what exists on a spool.
With us the material arrives in its raw form, as pellets. That allows us to process not only that one material in the print head but to introduce additives.
What an additive actually does
The simplest example is colour: a white base material with red colour powder blended in produces a pink to red part – depending on the proportion.
It becomes interesting when you change that proportion during printing. Picture a cube: the first layer is still white, from layer two onwards we blend in colour powder and gradually increase the proportion. The result is a continuous gradient from white through pale pink to deep red. The same principle works with any other property.
Three additives that matter in practice
- Colour powders for colours and colour gradients.
- Antibacterial additives such as silver particles.
- Blowing agents that foam the material.
The blowing agent is the most interesting lever here. Take a very durable, tough elastomer: foaming creates porosity, the material becomes flexible but retains high tear strength. It is precisely that combination that makes it usable for bandages and orthopaedic technology.
Where this is needed
Around 200 different types of plastic are in circulation, each with its technical application – transparent, food safe, durable, heat resistant. Sometimes it makes sense to change these properties deliberately to suit the application.
This is especially clear in medical and orthopaedic technology. No two feet are the same, no two bodies, no two seating profiles. For individual treatment with hard and soft zones, 3D printing is at an advantage anyway – but only blending allows those zones to be executed as genuine transitions rather than assembled from parts.
We are currently working on projects for wheelchair users where the seating profile is scanned and hard and soft zones are derived from it. With leg amputations, where a wound swells and subsides, we can respond individually – and where wound fluid or bacteria come into play, silver particles make the part antibacterial. More on this in our article on orthopaedic technology.
A thought experiment: the bespoke shoe
You can take this all the way. The sole has to resist abrasion from gravel and stones – so we print it with one head from the material in its original form.
Then we start blending in a blowing agent. A head with a large nozzle quickly lays down a soft midsole in high volume, which can already contain zones: firmer at the heel, softer in the middle, firmer again at the front – depending on what the foot looks like.
Finally another head takes over the fine contour and blends in silver particles, so the shoe stays antibacterial even with heavy perspiration or an injury to the foot.
When the geometry is not flat
A bandage is cylindrical, not a flat part. In our system one axis can be replaced by a rotary axis: the bandage is mounted and printed through a rotationally symmetric motion. That makes bespoke knee or elbow supports with hard and soft zones possible. How this works together with textiles is described in our article on printing onto textiles.
And when the part breaks?
Then it can be recycled. The part becomes regrind, and because regrind is also in pellet form we can blend it straight back in – within the process, with no detour via filament production.
Plastic is an excellent material but always carries the aftertaste of being bad for the environment. With this process the same material can be used several times over instead of being thrown away after one life. We have a separate article on regrind too.
Chapters in the video
The video is in German; the chapter titles below link straight to the relevant passage.
- 0:00 · Intro – what additives make possible
- 0:29 · Why pellets rather than filament – blending live
- 0:49 · ~200 plastics & their properties
- 1:18 · Individualisation: medicine, orthopaedics, footwear
- 2:07 · What are additives? (colour powder & gradient)
- 3:07 · Antibacterial & blowing agents: foamed structures
- 3:34 · Applications: supports, orthoses, wheelchairs, wound care
- 4:27 · Example: the bespoke shoe (firm sole → soft zones)
- 5:39 · Rotary axis: printing directly onto supports
- 6:18 · Recycling: blending regrind back in live
- 7:05 · Conclusion & sign-off