No, look: you completely missed the point. Here it is again, in lots more detail...
Every time you heat up and cool down a thermoplastic, its mechanical and chemical properties change. This is mostly because the volatiles in the plastic cook off when it's heated, but there are some other things going on at the chemical level that I won't get into. This is the reason why you can only use so much "regrind/recycled/reprocessed" plastic in a mix: It's already been heated and cooled at least twice in its life as a plastic (but probably many more times). It doesn't matter if you chip it up into little tiny pieces or cut it into "strips" - unless you chemically re-polymerize the plastic, it will have inferior properties compared to new, "virgin" plastic ore.
So, that's big issue number one. Still with me? Here are some more issues that I alluded to earlier, but didn't elaborate on:
Issue number two is any source of consumer plastic is going to be contaminated with biological stuff, probably whatever the container was holding, but depending on where the plastic has been it could have all sorts of stuff on it. And I'm talking about more than the chunks of leftovers or the skin of milk left behind in a milk jug: plastic is porous, so it will absorb whatever it is in contact with to some degree. If you want to reuse this plastic you absolutely must get it very clean. A trip through your dishwasher is probably not sufficient. Just a quick google search reveals that recycling centers use a multistage process.
And crucially, much of this plastic is chemically broken all the way back down to the monomer, which you would not be doing with recycled plastic for a reprap.
Issue number three is the quality of the base plastic would be unknown and highly variable. Not all plastic is created equal - One supplier's blend of ABS is not the same as another supplier's. For most of what commercially recycled plastic is used for this doesn't matter - it's used for cheap containers or other short-life packaging where the physical properties of the plastic are not very important.
This does not apply to reprap. Even if you don't care about the strength of the plastic after it's printed, other properties that matter a whole lot, such as the glass transition temperature, the melt flow index, etc,
would be completely uncontrolled. Let's play a mind experiment... Let's say we have a 5m long length of filament made from various recycled plastics. Along this 5m length the Tg could vary as much as 10 or 15 degrees, depending on contamination, mixing of the regrind chips, how well it was extruded, etc. Ask yourself how predictably that piece of filament is going to extrude.
Fourthly, based on your post it sounds like you want to cut strips out of some piece of plastic, and feed those directly into an extruder? I don't think that's feasible. You basically have 2 options for how you actually use this recycled plastic:
- You can grind it up, and extrude it into filament for use with the normal reprap extruder design. You could either build your own filament making machine (and spend a couple months dialing in a process to get consistent output), or arrange with a filament manufacturer to make you filament from your chipped up recycled plastic. Shipping for this option will, pardon my french, be a bitch.
- The second option is to design your own miniature screw drive extrusion machine that mounts onto your reprap. This has been done experimentally.
In closing...
You can (and probably will) argue until you're blue in the face that none of these things are impossible. I won't argue that, because that's not what I'm trying to get across here.
Technical achievability does not necessarily equate to a good idea on cost, effort, and efficiency grounds. Solving all of these issues to enable repraps to use some degree of recycled plastic would involve a high cost in time, energy, and money for minimal payback.
I agree that the need for filament is a weak spot in the reprap supply chain. However, at the moment I think it's the most appropriate half-way measure between using raw plastic pellets directly and keeping the cost down and the design of the extruder simple. The cost of the filament is pretty low considering how much you can make with one spool.
If you are still not convinced that using recycled plastic is an unsound idea, I encourage you to do some research into the technology of injection molding, which has a lot of overlap into the plastic handling and processing side of reprap.