recycled filament questions

I've seen some chatter about recycling 1 gal milk jugs to use as filament but all the info I've seen on this relates to grinding or chipping up the jugs to extrude filament sized strands to use on a reprap or some kind of bulk granular extruder that used the ground/chipped plastic directly. Has anyone tried to strip cut the bottles and use them directly in a modified extruder?? I have some plans, somewhere in my heap of stuff, for a simple razor bladed jig that will cut a continuous strip from a 2 liter soda bottle to be used to weaving craft items. I was thinking that if I could cut strips that were volume compatible to a 3mm filament and modify an extruder to feed this I might be able to get by with this in the repstrap to build the actual reprap instead of putting out cash I don't yet have for the filament. I'm not sure how long a strip I might be able to generate with such a jig but maybe you could even butt weld several together to get a fairly long piece.

Anyone have any ideas at the average length of filament used to print the biggest part of a reprap, not weight but actual length of the filament used.

Using 100% recycled plastic as feedstock for a printer is a bad idea for lots of reasons. For some of the potential problems, please see this page, particularly the "What adverse effects does increasing regrind proportion have on plastic properties?" section.

[www.ul.com]

This topic comes up with shocking regularity (about once every 3 weeks) on various locations (IRC, here, /r/reprap on reddit, etc). Like I said, there are lots of reasons this is a bad idea beyond the impact recycled plastic has on the physical properties of the overall mix. Some of them are logistical, some of them are just plain unsound in theory.

After looking at the web page you linked to I'm not persuaded that slicing up existing plastic and using it directly without regrinding or chipping will significantly 'damage' the plastic's characteristics. I wouldn't be changing the physical structure of a sliced strip of 'blown' plastic any more than I would a filament of 'extruded' plastic which is what is being produced and sold to Reprappers for use in the current reprap machines. (At least that is how I ASSume it is being produced, I can be and often are wrong so I welcome correction )

The only down side I can see is with a problem with the length of available plastic strip obtained from a plastic soda bottle or milk jug not being long enough to produce an item without multiple stops and reloading of new strips. If it were possible to butt weld or even overlap a joint that wouldn't jam up the extruder then this would improve the usefullness. The other thing I see as a difficulty is the feeding of so thin a strip of plastic. A possiblility I just though of is cutting a wider strip and feeding it through a 'U' shaped pinch roller and feed tube so that the roller forms the plastic strip into the 'U' shape and the feed tupe would keep it in that shape until it hits the hot end. A 'U' shaped piece of thin plastic would be much stiffer for pushing than the same width and thickness in a flat strip.

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.

... all this fuzz about adjusting every brand of plastic to the printer - and/or degradation of the materials through recycling cycles - let me think, FDM-fabbing is only an entry-technology in DIY-3D-printing ... but it's actually changing the world and our view on manufacturing and physical objects!

For me the most interesting fabbing technologies will use powder - either grinded/powdered plastics, lignin (made from wood), sand, ceramic dust, metall powders, and so on ...

Powder/dust can be used in inkjet-powderbed-printers, as filler in paste-dispensers, or directly as fabbing material in SLS-printers.

This will reduce the complexity of material/thermal properties drastically, as the critical parameters are the particle-size and the used binder (or melting/fusing characteristics with SLS), what's much easier to handle ...

And additionally the possible accuracies depends on particle size and smallest spot - what's in the range of ten microns, compared to some hundred microns with common extruder nozzles ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Are you this big of an arrogant putz on purpose or do you just have a nack of coming across like one?

If you are the normal on this board I guess I'm on my own.

Goodbye and good luck in your chosen career as keeper of all reprap knowledge and what can and should be done or tried. I deal with enough know it all assholes where I work so I sure don't have the stomach to deal with one in my spare time. But then again I'm sure you'll post a reply that will 'show' me.

... shouldn't be an affront - sometimes I'm probing the feedback with controverse ideas to get a feeling for the actual situation.

FDM-fabbing is a big thing but sometimes linmited in the possibilities - mostly regarding materials, rigidity and accuracy.

With some ten years experience in rapid prototyping and microtech my point of view is maybe a little bit different ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Victor
I don't think wpflum was referring to you, I do agree that polymers degrade with recycling, but the problems can be overcome, I worked in the moulding trade during the first oil crisis and we had to overcome the problems to stay in business,
so I would say do some experiments to find the practical problems and ascertain the solutions, then decide if its viable.
last year I worked on a project where I was told " it can't be done" but it is now a working system.

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Random Precision