I'm keen but it's not on my high priority list at the moment.
I'd be looking at using peltier effect with something like this:
to cool the raw plastic bits and then smash them through some sort of grate/small holes with a stored energy device. (wiki an industrial guilotine for an example) Not sure how low you'd need temperature to get nylon brittle though.
Also, you'd need to filter the output to exclude solids that could block your print nozzles.
I have many failed prints that could use recycling and I would gladly have smashed them into bits with a sledge hammer at the time
I know nothing about recycling filament however have seen plastic bags recycled into hoses used for garden watering systems. They feed the bags into a large solid steel auger that forced it through a heated die into water troughs for quick cooling. I think the whole chamber was heated and it was incredibly strong. It would be goodbye hand if you got caught in it.
I'm guessing you want to cool the plastic so it shatters into small bits to make feeding the auger easier? Would a preheat chamber that is at melting tempature as it enters the auger be an option?
I would imagine that something like the fillastruder would be what you would want to use.
instead of throwing beads/granules in there you would want to pre-grind up the plastic parts to have them uniform so they dont get stuck.
The biggest problem would be controlling what plastic you put into the machine. if it's recycled prints of your own then it's not too much of a problem, but recycled fillament would have very different properties to what you orignially printed with, simmilar to Diamond age's Virgin Black versus black fillament you get from othe suppliers where it is all the left overs re-melted and dyed
You could grind up reject parts using Liquid nitrogen to make them really brittle first. I think it really wouldn't be worth the hassle though. You'd only be doing it to satisfy some urge to save the planet, although it is questionable that it would be beneficial on that basis. It would probably end up costing more and results would be poorer than making your own filament from virgin pellets. Far better to put your energy into making your 3D printer reliable so you don't have so much reject stuff to send to landfill.
My Prusa Mendel i2 inspired Repstrap with welded steel frame: [youtu.be]
And my Smartrap derived Briefcase 3D printer: [youtu.be]
aprently you can do it with dry ice as well.
I would have thought something more along the lines of a shear rather than small scale like a blender.
You make a good point though, for example PLA is a biodegradable product (if composted correctly) having somewhere to send it so that it can be broken down, or knowing more about the process so you can attempt to do it at home would be a better use of our time, saving the planet wise.
also while we are at it, I'd be interested in seeing the whole process, from corn to fillament!