Very Informative! Nice work!
I’ve been looking to buy or manufacture a cheap twin-screw extruder for compounding/recycling my own polymers, but the price of our 11mm twin screw in the lab is sadly at 80.000€ at the moment and that isn’t feasible. If you manage to stumble upon a good deal for such an extruder, please let me know as the ones you listed are all single screw extruders!
I’d have a few things to add, which I learned working in the University Extrusion Lab in Paderborn here in Germany.
1. The heating of the extruder barrel is merely to keep the polymer in a molten state, as well as to homogenise the temperature of the extrudate. The main heat energy is dissipation energy coming from shear forces between the granules in the barrel!
2.When recycling household polymer waste, you have to deal with a lot of additives in the polymer that were specifically added for the product. E.g. a PET bottle consists of various layers (absorption, CO2 containment, etc.). You’ll also have to deal with these additives when extruding your own filament.
3. For each recycling circle, the molecular length of the polymer chains decreases, resulting in lowered mechanical properties. A good rule of thumb is that the properties become too bad to use after about 10 cycles. That’s why we only add a ratio of 40% recyclate to 60% when processing it.
4. Cleaning. Our extruder in the Lab uses a filter mesh as well as a vacuum degassing system to remove unwanted impurities in the product. I haven’t tested the mini-extruders you listed, but I fear that chemical and other residues might gunk up a printer nozzle over time, as they do tend to clog our mesh filters.
If you have any more questions, feel free to ask. I’ve got some experience to share!
