3D printing PLA question

[Marlin]

Does anyone have experience with melting away PLA?

BACKGROUND
A few years ago I was working on very small scale radio controlled
planes. Weight was fairly critical and one approach to building
lightweight airfames was to take a old plastic model and apply tissue
paper directly to the fuselage as in papier mache. Then after drying,
I'd slit the bottom of the shell and carefully remove the plastic from
the tissue paper. Inevitably the tissue would crinkle but the final
would smooth out so it didn't look too bad.


THE NEW IDEA
What would happen if I printed a sacrificial fuselage out of PLA, then
applied the tissue papier mache to the printed fuselage. The very
front of the fuselage would have a large hole and I'm imagining that I
could put the object in the oven and melt out the PLA. The oven
temperature would be fairly low, like 200-300 F. Does this seem like
a feasible approach?

Marlin

[Marlin]

I guess the one question I have is will the PLA ball up or liquefy?

[Jeff Hutchison]

This is a little different from what you're talking about...

http://clearmag.com/luxury/durapulp-a-world-without-plastic/

http://hackaday.com/2012/09/21/3d-printer-filament-made-of-wood/

 

BUT, I think that it hints at the possibility of this being a success with minimal discoloration and bonus strength if the PLA infuses into the paper!

 

Did you know that papier mache (accents notwithstanding) means "chewed paper"?  No wonder we don't translate it!.

 

Marlin

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[Jeff Hutchison]

As for the characteristics of the plastic in its molten state, I can safely say that it is quite "oozy" and that it should slowly flow out of the hole without any encouragement besides gravity.

[Charles Bornstein]

This is not directly on topic with regard to your project, but still may be interesting.

Here's a link to a page discussing using PLA as a substitute for wax in lost-wax casting.

The temps are higher than would be suitable for paper, but it still may be of interest.

http://3dtopo.com/lostPLA/

Charles

On Fri, Oct 5, 2012 at 11:23 AM, Marlin <marlin...@gmail.com> wrote:

Marlin

[Marlin]

Cool, this is encouraging. I think I will try to avoid the PLA
saturating the tissue paper if possible. The tissue will have been
soaked in Future floor wax (or whatever they call it now) and/or
Nitrate Dope so that it is essentially plasticized.

One trick I've done in the past is printing the paint scheme on tissue
on an inkjet printer so that the final layer of tissue adds the color
and markings.

On Oct 5, 11:40 am, Jeff Hutchison <jhutch1...@gmail.com> wrote:
> As for the characteristics of the plastic in its molten state, I can safely
> say that it is quite "oozy" and that it should slowly flow out of the hole
> without any encouragement besides gravity.
>

> On Fri, Oct 5, 2012 at 11:37 AM, Jeff Hutchison <jhutch1...@gmail.com>wrote:
>
>
>
>
>
>
>
> > This is a little different from what you're talking about...
> >http://clearmag.com/luxury/durapulp-a-world-without-plastic/
> >http://hackaday.com/2012/09/21/3d-printer-filament-made-of-wood/
>
> > BUT, I think that it hints at the possibility of this being a success with
> > minimal discoloration and bonus strength if the PLA infuses into the paper!
>
> > Did you know that papier mache (accents notwithstanding) means "chewed
> > paper"?  No wonder we don't translate it!.
>

[Marlin]

That's a great lost-wax story BTW. Thanks.

[Joe Kerman]

Lurker from sector67 in Madison, WI here.

Unlike ABS plastic, PLA has a really sharp dramatic transition from a
solid to a liquid. Where most thermoplastics will go from a solid, to
a gel of varying density. PLA goes instantly from a rigid hard
plastic, to a VERY runny liquid. So runny, that it can leak through
an otherwise tightly fitting threaded bolt. Leaking pla from 3d
printer hot-ends is a common problem.

You are looking closer to 375F (~190C) as a transition point for
melting out PLA. You might have to use silicone instead of wax paper
to pull it off, but its certainly a possibility!

Another thing to think about when working with PLA is that its
extremely "abrasion resistant". It will destroy sandpaper or any other
tools you attempt to use to finish it. (In fact, its very difficult to
recycle because it dulls the metal blades used to chop it up very
quickly)

[Francis Davies]

My experience with PLA is as follows:

I have put several large PLA 3D printed objects in the oven on a
baking sheet. At 175F (the lowest temp my oven can control to), the
objects become soft and saggy. Poking them with a stick shows that
they are sort of rubbery. They really are not liquid, though. When
the temperature was set to 375F, they did become liquid, but a very
viscous liquid. The edges of the resulting pancake shaped blob were
maybe 0.25" thick from viscosity and surface tension. This is not
like melting ice, for instance.

Hotter temps would certainly reduce the viscosity.

It would be easy to try this with PLA piece from the jar of random
pieces at the space.

Frank

[Mark Sullivan]

How about printing it with a soluble thermoplastic, like cellulose nitrate or polystyrene, and then rinse it out with acetone, MEK, etc?

- Dr Boom -

[Mark Sullivan]

> Cool, this is encouraging. I think I will try to avoid the PLA
> saturating the tissue paper if possible. The tissue will have been
> soaked in Future floor wax (or whatever they call it now) and/or
> Nitrate Dope so that it is essentially plasticized.

I think nitrate dope is mostly cellulose nitrate and cellulose acetate in an aromatic solvent.

If you printed the armature with cellulose nitrate and then dissolved it out,
you might dope the paper in the process.

- Dr Boom -

[Marlin]

That sounds like an interesting approach.  I do want to avoid temperatures above 400 F.  Can any of the lab's printers print cellulose nitrate?  Does it come on a spool?

One thing I'd worry about is the amount of solvent needed to dissolve.  There is a water soluable plastic that Greg was talking about for support material that could be washed away.  That might be cheaper and greener.

[Jeff Hutchison]

I found a source of 10' strings of nitro-cellulose... but you probably want to try printing with it using any of our 3D extruders:

http://www.dreamlandmagic.com/flash-string.html 

 

"Dr Boom" indeed.. haha!

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[Jeff Hutchison]

probably *don't* want... is what I meant to type, oops.