Does PolyMorph morph over time

I made a pen holder a few weeks ago out of PolyMorph, you can see it here [hydraraptor.blogspot.com] . I made it by pressing it into the corner of a folded sheet of metal while it was warm. When it had cooled I drilled a hole through it and the metal and bolted in on. As I remember it was a perfect fit. I removed it and left it on my bench for a few weeks. Now I have refitted it and it seems to be lose. I'd say it has shrunk by at least 1mm.

Can this be true or am I losing the plot? If so it would have dire implications for a precision machine made of it.

Edited 1 time(s). Last edit at 04/24/2007 04:10PM by nophead.

It shouldn't be doing that.

No but I think it has. I just removed it and had a close look. The bottom edge, which should be perfectly flat as it was cast against the sheet metal, is now quite curved.

I don't think it has seen any heat. The room window is north facing.

One question, is the volume of the object big enough so that it may have kept some heat inside it? Polymers have a big thermal inertia and if the volumes are big they will remain warm at the core.
Another possibility is that the material was stressed when cast. Over time, the stress may have been released, changing the shape.
It may also be that the polymer has undergone chemical reactions. This usually happens through oxidation due to UV radiation. I think this is less likely as the effects affect the surface more than the volume.
And of course, Polymorph may have a fusion point low enough so that at room temperature the flow is not to be neglected. Solid, amorphous materials may seem to be rigid, but they are solidified fluids, that change shape gradually.

****The bottom edge, which should be perfectly flat as it was cast against the sheet metal, is now quite curved.***

Ah! Now I see. You're looking at thermal contraction and distortion. This is something Vik knows a lot about with CAPA and I know a little about with HDPE.

Let me see if I can catch Vik's attention.

Here is the after picture [hydraraptor.blogspot.com]

I think I first used it the day after making it so it should have cooled by then and I think it was still flat at that point.

It was definitly stressed when cast because I pushed it into the corner of the metal and held it there while it set.

I was a bit worried at the time that I had squeezed all the water out.

I suppose I should make another one and monitor it.

Ah, so Polymorph has water in solution or suspension? Something like a gel or sol?
If so, variations in hydration may cause material changes over time.

I have seen the spectra of both Polymorph and Polylactic acid in the wiki. They are very similar indeed, and the differences at the infrared spectra could indicate interactions with water molecules in solution. Basically this could mean that Polymorph is PLA with some water content, to achieve a lower melting temperature. The drawback might be the volume changes you and Vik are witnessing.

The stress hypothesis might be worth investigating too, applying less/no pressure while setting.

Hot water is used to melt it. The instructions say to put the granules into hot water at 62C. When it fuses and turns transparent remove it with tongs and sqeeze the water out. I found it hard to melt with water at 62C so I used water straight out of the kettle. I assumed the water was only mechanically combined, not chemically but then I know nothing about chemistry.

I might try microwaving it next time, or is that a bad idea?

Edited 1 time(s). Last edit at 04/24/2007 07:03PM by nophead.

Do you have a "before" pic of that piece, nop?

A "before" image would help. I've made lots of things out of Polymorph, both splatted by hand and printed and I'm not seeing any deformity like you're witnessing. It does shrink on cooling, but I've only really noticed that when shaping it around a rod - you have to slit it to relieve stress.

Parts of Zaphod that were made in hot water have been functioning fine for over a year, and some replacement parts in my blender have been fine for 2 years. Now though I tend to use a fan heater. Is it hard to reproduce the part? Some experimentation would seem in order.

Vik :v)

Nophead: yes! definitely try microwaving, i would be very interested to see those results.
try low power settings first: defrost, then low power heater. short exposure time-frames.
Microwave radiation should not alter the chemical properties of the polymer as long as the temperature doesn't raise to high.

Having used 100

Oh, by the way: when doing the Microwave heating, just put a glass of water next to the polymorph. This is just a safety trick, to ensure that any excess microwave radiation will be absorbed by something.

Happy experimenting!

Forrest, Vic,
The best "before" image I have is here [hydraraptor.blogspot.com] but it is taken from the wrong angle to show the flat surfaces and it was already a couple of weeks old by then I think. The bottom and back faces were flat and at right angles when I last used it though because the pen was locked solidly. Now it spins around the single bolt because the back face is no longer in contact with the metal. I could just put a second bolt through it, but in the interests of science I will make a new one using microwaves this evening. I will try to take a decent before photo this time but photographing an amorphous white thing with rounded edges does not work very well.

Fernando,
Thanks for the tips.

One thing that surprised me the first time was how solid it was when I started with with water at exactly 62C. Having learnt since that plastic has a high specific heat capacity I probably used too small a water to plastic ratio.

As promised I made a new pen holder in the microwave.

Conclusions: Well I wouldn't recommend microwaving as a way of melting PolyMorph because it is not even enough. The outer edge, where it is in contact with the glass dish, is a lot cooler. Also it does not absorb microwaves anything like as well as water does.

I think most of the shrinking and curling occurs when it first cools down but I can't explain why the first one can no longer be locked in place. Maybe there is some further shrinkage over the long term.

Full writeup here: [hydraraptor.blogspot.com]

was it ever exposed to any warm temperatures that may have allowed it to melt/flow? even something like sunlight may have caused it if it was sitting out for a while. or if it was on a metal counter that got hot during the day... over the course of a few weeks it might have melted gradually to what you have now.

Zach,
No it was lying around on my desk in a room with a north facing window so it never got any direct sunlight. I doubt that it ever saw anything above 25C. One possibility I have thought of is that perhaps I bolted it on before it had finished shrinking, leaving it under tension against the metal. When I removed it it was allowed to relax and so no longer fits.

Interesting results with the microwave.
It seems that there is no significant water content in Polymorph, nor many oxygen hydrogen bonds, wich are the ones targeted by microwave radiation. So Polymorph is not a sol or a gel and will not undergo changes due to water loss.

If worst comes to wort, just put a nail or piece of stiff wire in it. That'll stop it curling!

Vik :v)