PLA vs. Methylene Chloride: Joint Peel Strength

The only commonly available PLA adhesive seems to be methylene chloride, which is common only because it’s part of really nasty paint stripper that actually works; I suspect you can’t buy the pure stuff anywhere.

Anyhow, I picked a pair of flat line width test plates from the PLA scrap pile, dabbed paint stripper on each, and clamped them together overnight:

PLA test coupon - clamping

PLA test coupon – clamping

Unlike acetone on ABS, paint stripper doesn’t actually combine the parts into a single fused unit; I could peel the two plates apart with some effort:

PLA test coupon - paint stripper adhesion

PLA test coupon – paint stripper adhesion

That picture shows the results of two glue-and-peel tests, with much the same result along the top and bottom edges. Some solvent damage appears as a thin white line around the edge of the glued joint, but with some care that wouldn’t be too bad.

I think paint stripper makes an acceptable adhesive for PLA, at least for joints that aren’t subject to peeling loads. You must design an interlocking mechanical joint, perhaps filled with epoxy, to withstand peeling loads, which isn’t nearly as good as the ABS option of just fusing the parts together.

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    • #2 by Ed on 3-May-2013 - 10:27

      True, but down at the bottom of that description we find, in red letters:

      This item is sold and shipped to schools and businesses only. Not available to individuals or residential addresses.

      So mere civilians can’t buy the pure stuff these days…

      • #3 by Jason Doege on 3-May-2013 - 11:47

        It’s not very hard to incorporate. I maintain a corporate shell from when I was an independent contractor. It might be a bit expensive if this was the only reason you did it but if you ever do consulting work there is plenty of reason right there.

        • #4 by Ed on 3-May-2013 - 12:42

          if you ever do consulting work

          Been there, done that … [grin]

        • #5 by polytechnick on 4-May-2013 - 22:07

          That would appear to be a whole lotta trouble to go through for what is a rather simple operation. If the goal is to simply join two pieces of (mis?)printed PLA parts, rather than necessarily fuse them together, a simple epoxy resin will do splendidly. It adheres well and FDM prints provide plenty of surface area to grab onto.
          I actually find adhering parts together by dissolving them at the joint to be a rather difficult approach and would prefer a solution that does not require, ahem … dissolution (pardon the pun) every time simply because it’s easier to apply, control and check results of.
          As far as I can tell, the only time adhesion by dissolution might be required is to join pieces of optically clear plexy or acrylic or another such material for a joint that does not obstruct the view. It’s hard to call an FDM-printed PLA part of any shape “transparent” as such and so any clear epoxy resin would do just fine as the adhesive.

        • #6 by Ed on 5-May-2013 - 08:22

          a whole lotta trouble

          I’ll grant you that… and it’s toxic, too!

          FDM prints provide plenty of surface area

          I try to put the joining surfaces on the bottom (platform) side of each part, so they come out with (ideally!) glass-smooth surfaces and precisely positioned holes for alignment pins. For example: helmet mirror mount, triple-cylinder thing, and blinky light mount.

          Those flat surfaces don’t provide much room for an epoxy film (although perhaps I shouldn’t be so generous with the stuff), which is why I like a thin application of solvent to each surface, followed by clamping: good alignment, invisible joint, and perfect fusion.

          I loves me some epoxy, though, so I should think about adding narrow recesses across those surfaces. The unsupported interior surfaces would be wonderfully rough and, assuming the alignment pins do their job, the epoxy would hold the parts together without requiring any adhesive near the visible edges. Sounds like a win to me.

          Thanks for the nudge!

  1. #7 by Red County Pete on 3-May-2013 - 11:45

    For the marginally suicidal really intrepid, there’s a YouTube video on how to distill methylene chloride from paint stripper. Shows up on a search “Jasco methylene chloride stripper”. (Needs the brand name for the search to work right in Bing.)

    The video I mentioned is this (youtube dot com/watch?v=h50gn_VUpT0). Looks like Jasco is now selling non-methylene chloride strippers, but they were the biggest supplier of the goop on the Left Coast for years. Note: with my dialup connection, I don’t do videos, so no idea on the utility of the content.

    • #8 by Ed on 3-May-2013 - 12:41

      Much to my astonishment, methylene chloride boils at 40 C, well below acetone’s 56 C… so all you need is gentle heat.

      Not that I’m going to try it, mind you: the failure tree rooted in a can of paint stripper atop a hotplate seems much too bushy!

  2. #9 by Red County Pete on 3-May-2013 - 12:01

    I think I triggered the spam filter on a youtube video on distilling methylene chloride out of stripper, (search for “Jasco methylene chloride stripper”) but a search on “distilling methylene chloride” brings up the bit that the other ingredients in stripper are water soluble, while dichloromethane isn’t. Not sure how much of the “bad” stripper is out there, but I’ve seen it in gallon quantities at Home Depot as of a couple months ago. Must have been the right stuff; the cans were starting to buldge–one of the reasons why I won’t use it anymore.

    We use a private mail box for receiving stuff, but I think I’d get in trouble with hazmat orders…

    • #10 by Ed on 3-May-2013 - 12:36

      triggered the spam filter

      I set it to trigger on anything that looks like a URL, which gets rid of essentially all the spam. Other than that, I have no idea how they tag things; of late, I’ve seen a bunch of obvious spam that must be close enough to standard English to evade the rough-cut tests and appear in the moderation queue.

      It’s up now…

  3. #11 by david on 3-May-2013 - 15:09

    The interwebs say: ” PLA is soluble in chlorinated solvents, hot benzene, tetrahydrofuran, and dioxane”. Gee, I can’t think of any problems there!

    But, actually. THF ought to be available in the form of PVC glue, and is rather safe as long as it’s peroxide-inhibited and you don’t store it too long or distill it.

    http://www.e-zweld.com/webresources/files/msds/pvc_1.pdf for example.

    I wonder if that would give a better bond.

    • #12 by Ed on 3-May-2013 - 18:46

      The interwebs say

      My search-fu must be weakening, because I didn’t find any of that.

      tetrahydrofuran

      My can of PVC cement dried up, but THF is the last ingredient in Purple Primer… which actually softened the surface of two more of those little PLA slabs, which are now clamped together. PP looks awful on natural PLA, but if it does a decent job of bonding, that makes up for a lot.

      [Update: Works perfectly and produces a fused joint that I can't pull apart!]

      Next time out, I’ll pick up some clear PVC cement (in the lowest viscosity version) and see what happens.

      Thanks for the tip!

  4. #13 by equinoxefr75 on 4-May-2013 - 01:36

    Hi,

    II used pvc cement to glue pla. It works pretty well.

    Regards

    Pierre

    • #14 by Ed on 4-May-2013 - 07:49

      It works pretty well.

      Indeed it does!

      I tried some Purple Primer yesterday and this morning I can’t peel the joint apart: that’s good enough for me!

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