3d pellet suppliers need to look into this. Perhaps they are milking the relatively new
market for flexible filament.

My scrounging interests go further into use of recycled rubber and plastic cross linked
to become TPE.
Here is  one outfit that do it entirely from recycling, cryogenic, no added chemicals.
http://www.rticryocanada.com/technologi … -blending/
and
http://www.enduraprene.com/

I have purchased a mini shreader, and have successfully produced granular that will flow down
a hopper into my filastruder #1632.  I takes a good two hour effort to manually grind pet and hdpe milk bottles.
A good arm exercise. A motor would double the shreader costs, and this is just a low level expensive filament
replacement experiment, costing about 20 da vinci 600g filament cartridges. 
I would discount the shreader as that has a lot of uses outside 3d printing.