Friday, July 15, 2005


Polylactic Acid

We recieved a sample of polylactic acid in the mail today. Some preliminary tests with a bowl of boiling water and a hair dryer on max setting were conducted. Results are as follows: It doesn't melt.

Using a k-type thermocouple probe, we checked the temperature put out by the hairdryer at 120C (approx.) At this point a few grains started to turn transparent and welded to one another.

As we have no way of making polylactic acid rod, we can't quite feed it through our extrusion nozzle. Yet. Time to bake polylactic acid cookies...

Vik :v) & 4sh

I've actually had reasonable success today melting and extruding polyethelene using a variation on you guys' extrusion head. It was built around a copper pipe, with plaster of paris substituted for the PTFE tape and no PTFE rod, and some nichrome salvaged from a toaster. Quite a bit less of an elegant setup, admittedly, but it did get hot enough for me to jam some cut-up milk bottles into it, melt them, and both extrude and draw material out the other end. Oh, and there wasn't so much risk of heinously nasty chemicals coming out if I overheated it :)
It might be quite worthwhile to look into building a self-heating unit to preprocess material at temperatures above 100 C and easier to manage than a hairdryer...
Plaster of Paris is a very good idea. I suppose cement might work too? Or clay?

If you've got any pictures, I'd like to see them.

Vik :v)
I'll see if I can get pictures about.
As for the cement and clay, certainly they ought to work - the cement might be a smidge more awkward to work (plaster of paris can make a very nice, spreadable paste if you don't use much water), but the clay certainly ought to work nicely.
Both might also not do the slight browning I'm seeing where I've got nichrome near the surface.
I've actually gotten some portland cement-based bricks to decompose before with heat, but that was by bringing them up to glowing orange several times. If you get the right clay, though, you could run molten glass through it without too much trouble...

Now I'm all off thinking about a high-temperature head for glass rod... *sigh*. lol. Make it out of a good clay or something else that'll take the heat, run a propane blast through it and pack it in refractory insulation... it might even work. Maybe. Perhaps have an industrial manufacturer make little 1x1 cm thin tungsten cups with a hole in the bottom, and build a ceramic insulator/burner/etc around it...
Okay. Enough insanity.
I've put a couple pics up at my until-now unused blog.
Having made one, how small do you think it would be practical to make an HDPE milk bottle squirter? I'm not much bothered if it's not up to fine work - we'll need the RepRap equivalent of "cast iron" parts in any event, so any trick that works is a good one.

Any plans to push the plastic out with something?

Vik :v)
Well, the only way thermally this differs from the extrusion head you guys have is that it's got insulation that's not as easy to work with and ought to be able to do higher temperatures safely.
What I'm thinking is that separate from the machine you've got something that looks vaguely like a pot, where you put whatever form of HDPE you've got lying around, which is kept at a reasonable temperature for melting the plastic.
You either draw out or use some sort of drive mechanism to push/pull a relatively thin rod out of that mass of plastic. Then you run that through variously sized nozzles on the machine.
This was more me just finding out if I could make such a thing functional than a proper prototype.
Well you seem to be getting results. Keep it up!

Vik :v)
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