Recycling 3D printer filament isn’t a new idea, and in fact there are quite a few devices out there that will take chunks ABS, PLA, or just about any other thermoplastic and turn them into printer filament. The problem comes when someone mentions recycling plastic parts and turning them into filament ready to be used again. Plastics can only be recycled so many times, and there’s also the problem of grinding up your octopodes and companion cubes into something a filament extruder will accept.
The solution, it appears, is to freeze the plastic parts to be recycled before grinding them up. Chopping up plastic parts at room temperature imparts a lot of energy into the plastic before breaking. Freezing the parts to below their brittle transition temperature means the resulting chips will have clean cuts, something much more amenable to the mechanics of filament extruders.
The setup for this experiment consisted of cooling PLA plastic with liquid nitrogen and putting the frozen parts in a cheap, As Seen On TV blender. The resulting chips were smaller than the plastic pellets found in injection molding manufacturing plants, but will feed into the extruder well enough.
Liquid nitrogen might be overkill in this case; the goal is to cool the plastic down below its brittle transition temperature, which for most plastics is about -40° (420° R). Dry ice will do the job just as well, and is also available at most Walmarts.