Material: Polystyrene

Hi,

Since I'm waiting on shipments to start building the RepRap, I have been trying to make and evaluate plastics as a source material.

I have been trying to make them from starch by adding vinegar and some glycerin, but the result seems to lack real plastic properties such as strong cohesion of the material (it's still crumbly). I used these instructions:
[www.instructables.com]

Then I found another instructable to reuse polystyrene:
[www.instructables.com]

It is essentially the usage of waste styrofoam (not really recycled in practice anyway) to give it a second life as a usable polystyrene. Putting it in aceton will solve it and let out the gas that makes it this light material.

I don't know what the material characteristics for extruding it would be, but perhaps someone has tried it already?

I might make some polysterene from foam tomorrow. In a closed can, it seems that you can keep it stored for a while (see linked article).

Just wanted to share this. (I hope I'm not duplicating an old discussion here)

Regards,

Erik de Bruijn
Hopefully RepRapping soon...

Regarding the potato - sorry, starch plastic, have you also tried the HCl / NaOH variant? Idea is to use hydrochloric acid instead of vinegar and netralising it with sodium hydroxide. Look here:

[www.chemsoc.org]

No, I've not yet tried any of those two methods. But I'm curous anyway. The non-vinegar recipe has the advantage that no odor would disturb my wife. ;-)

Howie

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Airspace V - international hangar flying!
[www.airspace-v.com] for tools and toys

I seem to recall reading somewhere on the internet that a way to make improvised napalm is to dissolve polystyrene foam into petroleum until you get a suitably sticky flammable gel/slop.

So I guess for folk who have difficulty getting hold of acetone, petrol may do instead.

I can't say I have ever really ever tried though, legitimate uses for napalm in Suburban UK are severely limited

Let us know how you get on though in using this as a way to recycle Styrofoam into useful plastic.

aka47

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Necessity hopefully becomes the absentee parent of successfully invented children.

It could be usefull if we solve some major problems: the bubble formation of evaporating solvents and to get the evaporation to be uniform. Also, we need to get rid of all the acetone from the room, so ventilation will be necessary. It would be desirable to remove all the acetone in the mix to get a solid body. This would probably shrink the printed layer in some way, as we reduce the volume of extruded material by at least the amount of solvent it contained.

... when heating the topmost layer to evaporate the solvent (IR-heater or hot air) then it should shrink mostly vertically, so you should calculate the layer-hight/slicing with this shrinking.

Horizontal shrinkage should be in a very low percentage, when layered on a complete hardened surface.

Another excelent point should be the good interlayer adhesion, as the acetone re-solve the surface of the the underlaying layer, so it should form a perfect bond.

Viktor

Acetone

I know it is a lot of trouble and possibly not possible or expensive but acetone recovery as well as heating the air would be better than dumping it out to the environment.

Possibly using a peltier module to cool outgoing air from a fume proof enclosure and dumping the heat into warming the incoming air to the enclosure.

This should also accelerate solvent evaporation.

Filling the polystyrene slop with something that doesn't dissolve in the acetone may help with shrinkage (Usual lineup of fillers used with polymers perhaps) and bulk it out a touch.

cheers

aka47

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Necessity hopefully becomes the absentee parent of successfully invented children.

Hi,

... i tried with polystyrene (styropor) solved in acetone:

It's very easy to dissolve - simply put as many foam in the acetone as you want.

When the foam dissolves it morphs to a paste with a fixed amount of acetone in it, the other acetone stays as separate fluid phase and didn't mix/solve, so you can extract the paste and let the not embedded acetone in the pot.

Then i put some paste in a syringe and tried to output some trays manually:

It's possible, but you have to apply much force with thin needles - so i tried a yellow type with 0,8mm OD (=Outer Diameter) and a green one with 1,3mm OD.

The paste didn't stick very well on not acetone-solvable materials, but stick excelent on styropor.

With thin trays it's a very good basis, with thicker trays (>1mm) the acetone in the paste start dissolving the basis too, so the trays sinks into the styropor.

When releasing, the stuff forms very fast a dry skin and dries in some minutes to a selfsupporting soft-elastic solid, so you can output the next slice and it sticks very good to the dried surface beneath.

A bad point is the forming of very strong cobwebs which didn't rip apart, so the releasing at the end of a tray has to be optimised.

When heating with hot air, then be carefully - over 50

On heating

Is heating actually really really necessary ??

Ambient temperature airflow (room temp approx 19 to 21 deg C) so long as the air flow is increased should be sufficient. You are only really needing to carry a way the vapor so more can evaporate and ensure that the paste doesn't get too cold (evaporative cooling).

If heating the air flow 35 deg C should be more than enough, with as you suggest thin layers. (Layers is what I think you mean by trays ???)

Thoughts for what they are worth...

aka47

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Necessity hopefully becomes the absentee parent of successfully invented children.

Hi Andy,

... i tested with heating for faster hardening, it's not essential when you wait between the slices until it's hard enough ...

Today i tried the hardened polystyrene - it's complete hardened, but stays brittle, so i't not such a good material for fabbing.

I think it's more suitable for sacrifice mold-forms or as support-material.

Viktor

I think ABS can also be dissolved in acetone. I wonder if that behaves in a similar way but ends up with a stronger result?

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[www.hydraraptor.blogspot.com]

... ABS should work much better - AFAIK after solving in acetone and complete drying it's around 70% the strength of bulk (e.g. extruded) ABS.

I used this sometimes to glue together or repair ABS-elements ...

Viktor

If you were to deposit layers of solved ABS and purposefully heat them above 50C you could create an interesting material; light, rigid, thermal and sound insulating and possibly useful as a sacrificial shock absorbing liner. Just a random thought.

What about creating a light underpressure in an airtight volume to accelerate evaporation?
I envision some kind of a vacuum pump sucking air out of the reprap and condensing/recycling/disposing the solvent out of the air.