I recently came across this industrial grade meet grinder. Its located in a laboratory used for, among other things, injection moulding.
I’m told that its used to grind plastic granules down into a fine powder. What is particularly interesting though is that this will only work if liquid nitrogen is poured in while it is grinding or else it will quickly become jammed. It seems the liquid nitrogen cools to the plastic (−196 °C, 77 K , −321 °F) and so reduces its fracture toughness and allowing it to be broken into smaller pieces.
So is this a practical approach for those at home wanting to attempting to recycle their own plastic for use with a 3D printing? Obviously not all of us have access to liquid nitrogen or even dry ice, so would a home freezer provide much of an advantage?
I was unable to find any useful information on the deformation properties of HDPE, ABS or PLA at low temperatures in the limited time I have available and so its difficult to tell if a domestic freezer (-20°C?) would be cold enough to make a usable difference.
If anyone wants to put on their science hat and undertake a few home tensile tests on a short lengths of 3mm filament to produce a stress-strain curve at low temperatures and at room temperature it could provide interesting results.