Thursday, July 28, 2005
How exciting. After a mix-up with NZ Post, a sample of 210g of PLA arrived for me to play with today. Thanks Vik!

I thought I'd check out the behaviour of the PLA. It turns out it melts at a much higher temperature than I expected. I expected it would melt between 130°C and 180°C. Here's what I found:

155°C starts to become noticably glassy, but granules are still quite hard.

170°C starts to deform

180°C granules merge together very slowly (still too viscous to flow in any useful way)

185°C slowly flattens to a single continuous mixture, but still very viscous. Quite meldable at this stage though.

200°C still quite viscous

230°C still quite viscous. I'm not sure it will extrude easily at <1mm thicknesses.

At this point there was a little bit of a smell, so I thought I wouldn't push it too much futher. Beyond this point becomes less useful in any case.

As far as mechanical properties, this stuff is very tough. Should certainly do a good job for a lot of parts. It's a bit harder than I expected, but also more brittle. I think those are usually traded off against each other, so no big surprise. If we can make our own, we may be able to tailor that to our taste. The brittleness doesn't seem like a problem, you have to apply quite a lot of force to crack it.

I also discovered it adheres really well to things. The small sample I melted in a ceramic container wasn't coming out and reheating only gets some of it out. I thought I'd try breaking the container around it on the offchance it would come free. It's well and truly bonded however, so that sample is ruined (getting the fragments of ceramic out will be next to impossible now). Something not to try again...

Good adhesion is a promising sign really since it means objects we create will probably be strong (lots of extruded rows need to bond together).

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