Filament scrap as filler: Thoughts on re-use
That "other thread" got off on a weird tangent, but it occurs to me that scrap plastic might be a useful filler for weighting and strengthening large parts without lengthy and filament-intensive infill printing. My thinking is that one could simply create a slurry of shredded scrap plastic -- no need to even sort by type -- that can be injected into either a partial print, a mostly-hollow-print with filler ports or a multi-part print and you've got a good use for scrap filament and even shredded spools, all of which is difficult if not practically impossible to recycle. No need to shred to the level of refinement needed to create filament, but get parts down to "microplastic" size and squirt it in where needed.
The idea of creating a slurry of messy , expensive and temperature-sensitive epoxy that requires elaborate handling is (IMO) overly complicated, but some sort of room temperature injectable resin or glue might be practical. Grind up scrap plastic, mix it into a slurry with some sort of semi-fluid carrier and inject it into printed parts using something like a turkey baster (Stefan used a syringe in his CNC Kitchen post) should work.
I'd welcome any thoughts on what that less-messy, less-temperamental carrier fluid might be. I suppose thinned white or wood glue might be a good candidate for low-mess, low-temp and easy cleanup from mistakes. Hell, even plaster-of-paris might work though I'm trying to think of something a bit more pliable. Also any simple process for shredding scrap plastic down to small sizes are welcome. Thoughts? Looking forward to open discussion.
Edit: Bird-shot could be mixed in for added ballast.
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He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan
RE: Filament scrap as filler: Thoughts on re-use
I don't think you'd want to use anything that sets up hard or you will run into issues with thermal expansion/contraction rates. Wood glue shrinks as it cures, and many casting resins or epoxies get too hot if you cast large volumes at once.
My immediate thought is to use common silicone. Add a few drops of glycerin to aid curing the internals of such a solid mass, and you should be good to go. Bubbles and voids may be a concern if using the stuff from a tube but there are mold making options available that are thinner and should flow more smoothly. If you design the part with an internal texture to give it some grip, that may also aid the end result.
RE: Filament scrap as filler: Thoughts on re-use
I don't think you'd want to use anything that sets up hard or you will run into issues with thermal expansion/contraction rates. Wood glue shrinks as it cures, and many casting resins or epoxies get too hot if you cast large volumes at once.
Good points!
My immediate thought is to use common silicone. Add a few drops of glycerin to aid curing the internals of such a solid mass, and you should be good to go.
Perhaps something like caulk or silicone window sealer? A "fill your own" caulk tube might work as a applicator. (Edit: They exist!)
Bubbles and voids may be a concern if using the stuff from a tube but there are mold making options available that are thinner and should flow more smoothly. If you design the part with an internal texture to give it some grip, that may also aid the end result.
I'm not sure bubbles would be too much of a concern so long as the injected slurry is flows easily enough to fill most voids. I suppose the scrap plastic is more of a "feel good" addition, but much like carbon-fibre or glass-filled filament, I like to think it would add some strength.
Perhaps I should spend some time in a home improvement or crafts shop. I'm sure the basics are problems that folks have solved long ago.
Thanks for the feedback. This is an interesting "multi media" approach.
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He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan
RE: Filament scrap as filler: Thoughts on re-use
In researching thinning silicone, I found a helpful post... on a Mermaid costume forum of all places. It's apparently a technique for making tails.
"Wicking action silicone" is a thing in car repair as well. A bit pricey, but interesting.
This is going to be another deep rabbit hole.
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He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan
RE: Filament scrap as filler: Thoughts on re-use
There are a multitude of resins, some that claim no expansion or shrinkage during cure. Some weighted with metals. Some even conductive. Some not so exothermic.
Injection is the issue I see, the part would need to be well designed to handle the process, special openings made that will seal easily after the pour.
Then comes old plastic prep... how many of us have grinders capable of reducing a part to something on a micro-plastic scale. Will an old coffee grinder do? Mine is too small even for my test parts. Blender, food processor, maybe? Also need to think about density and how the reused plastic bonds and mixes with the carrier - floating bits won't work well.
But once you need to start adding resins as a binder, it's a rather silly idea to reuse the plastic scraps. A method to add really needs to be thought through, and not be something that breaks the entire FDM process. A second nozzle for example that takes chipped plastic, melts it down and extrudes it similar to the primary nozzle, but strictly tuned for volume infill. Anyone for a dual direct drive extruder??
RE: Filament scrap as filler: Thoughts on re-use
Some quick research has me thinking a good old manual meant grinder might be sufficient, at least to generate some testing samples.
Worst-case, 2 part prints that snap permanently together should work. For a bust, the base could be open at the top for filling, then the head snapped on.
I'm going to re-watch Stefan's video. I think he was able to fill cubes with gyroid infill without too much fuss.
and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan
RE: Filament scrap as filler: Thoughts on re-use
One of my projects I never got around to finishing was a plastic injector molder. Mostly angle iron construction.
It used chopped up plastic; milk cartons were the material of choice.
Certainly sounds like like your scrap would work. Right temperature range.
This PDF describes it:
RE: Filament scrap as filler: Thoughts on re-use
The area of concern is the infill gap vs chopped plastic size. 1:1 won't work, 1:1.5 will probably still have flow issues, 1:2 might have a chance, and 1:3 is my guess for basic minimum to get the bits inside the infill (if the bits are spheres). Then add in viscosity of the binding agent, 1:6 is probably minimum for things to simply flow. Even then, vacuum fill is a reasonable requirement to get material evenly distributed. That almost implies a need for a form... But since bits will be chips, with sharp edges that like to hook onto things, mincing to 1:20 or even 1:50 is probably going to be needed.
Maybe the best use of old plastic is for use as an agent to break up hard clay soils, something like vermiculite. PLA would be relatively harmless, PETG a tad bad, ABS a bit worse... but probably a better place for it than as microstructures in the ocean food chain.
RE: Filament scrap as filler: Thoughts on re-use
Grinder anyone??
RE: Filament scrap as filler: Thoughts on re-use
This might be good as the first stage chopper - used to produce bits small enough for the typical meat grinder inlet. But a bigger processor may still be needed for parts > 100 mm.
Waring has a commercial food processor that has an optional metal bowl... bit that adds up to $600+.
Found this small cheap unit in metal: https://www.amazon.com/dp/B07GWFFKWV
RE: Filament scrap as filler: Thoughts on re-use
Grinder anyone??
That'd surely work, but I was hoping to keep it below the cost of a printer (or two). Need to find an old manual cranked meat grinder at a garage sale.
I'm not so worried about a perfect fill, but will definitely go with low infill or even manually designed internal supports. Weighting the base is the main thing.
and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan
RE: Filament scrap as filler: Thoughts on re-use
Under $20, adds plenty of weight for less than the cost of a used meat grinder.
https://www.amazon.com/Silver-Zinc-Plated-Metal-4-5mm/dp/B01E9JUGU6
or maybe this raw material:
RE: Filament scrap as filler: Thoughts on re-use
Wow - found this deal, the hex shape might be best since it will pack a bit better - and only $4 a pound.
https://www.rotometals.com/zinc-hexagonal-pieces-99-995-1-pound/
RE: Filament scrap as filler: Thoughts on re-use
Interesting options. It just dawned on me that a sand slurry would probably work for weighting purposes. The stuff sure manages to work its way into every crevice after a day at the beach.
and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan
RE: Filament scrap as filler: Thoughts on re-use
Sand is actually a good option; and resins that will work with it as a binder are readily available. But I'm curious as to why most urethane mixes say do not use wood stirrers ... seems that sort of eliminates them for PLA compatibility reasons - cellulose is cellulose, no?
RE: Filament scrap as filler: Thoughts on re-use
PLA isn't cellulose, it's polymerized lactic acid. Chemical structures and properties are *very* different.
(Cellulose is polymerized glucose)
RE: Filament scrap as filler: Thoughts on re-use
PLA isn't cellulose, it's polymerized lactic acid. Chemical structures and properties are *very* different.
(Cellulose is polymerized glucose)
Interesting (and thank you for the correction). Somewhere I read PLA is plant based, and I glommed onto cellulose as the natural base material. Now I have to go back to the books and actually read the material carefully. Darn.
RE: Filament scrap as filler: Thoughts on re-use
PLA isn't cellulose, it's polymerized lactic acid. Chemical structures and properties are *very* different.
(Cellulose is polymerized glucose)
Interesting (and thank you for the correction). Somewhere I read PLA is plant based, and I glommed onto cellulose as the natural base material. Now I have to go back to the books and actually read the material carefully. Darn.
My guess (as a chemist,among other things) is that it's probably a resin cured by a catalyst. There are a few possibilities as to why wood stirrers might be advised against, some of the more common ones being:
- Cellulose has (somewhat) similar ring structures to polyurethane and the curing catalyst is poisoned or trapped by it, causing your pour to not set properly
- The hydroxyl groups in the cellulose are liberated by the resin and form water and/or hydroxide anions (base). Or, even just the natural moisture present in the wood, since it is a porous material. Water and many resins do not mix as it can cause things like rapid heating, boiling, or producing unpleasant fumes. Changing the pH of the mixture can also have all kinds of fun results.
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RE: Filament scrap as filler: Thoughts on re-use
Thanks! Always enjoy learning new things.
RE: Filament scrap as filler: Thoughts on re-use
fast setting glue like uv activated ones seem like a good way give the scraps good adhesion