Saturday, July 30, 2005


PLA thermal characteristics

After receiving some sample PLA from Vik, I thought I'd just see how this stuff behaves at our extruder temperatures.

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.

I didn't test further than this because the current extrusion system won't be very happy at any higher temperatures.

This suggests the PLA is an extremely high MW sample. In all likelihood if we can produce our own PLA it will have a lower melting point. In fact we might have the reverse problem where we can't get it high enough.

An odd thought just struck me. Not sure if it would be useful but.

Fishing line is essentially a spool of thin extruded nylon. Readily available in reasonable quantities. I also found a site that lists spools of polyethylene monofilament among their products. It seems like this would be relatively easy to feed into a deposition head.
In a similar vein, there are spools of Strimmer/Weedeater line available in slightly larger diameters. It might be fun to see what the MP of some of those are too.

The main problem with high MP materials is the high viscosity. This leaves trails over the machined artifact like spiderwebs.

Vik :v)
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