Powder Appearing On Fud After Storage

Discussion in 'Finishing Techniques' started by Model_Monkey, Dec 5, 2016.

  1. Cygnus3D
    Cygnus3D New Member
    I agree. I got some stuff over a year ago, and it turned powdery white as soon as I dried after the ultrosonic cleaner. I was able to paint the part with no issues and no reall loss of detail, so I guess this stuff is very variable.
     
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  2. mkroeker
    mkroeker Well-Known Member
    I see a hamster wheel turning here - stuff turning white as soon as it dries after cleaning is either showing surface corrosion from use of aggressive solvent (heptane) or areas that were in contact with support material (hence rough, and the presence of oily or waxy material of sufficiently similar index of refraction in the gaps will make it appear smooth and translucent). This is most likely not the "crystal growth" that some people see appearing on their once-perfect models weeks or months after painting them.
     
  3. matthewc83
    matthewc83 New Member
    Hi all,

    First off, thank you for the great discussion on this issue and providing good examples/pictures that helped us really identify some key details to help characterize the problem. The FUD-NY production team is aware of the concern surrounding this "crystallization" issue and I have been actively investigating it. That said, the point of this post is then twofold: first to help you all understand the nature of this "crystallization" and second to suggest a solution based on the findings, so bear with me for the long-ish post.

    Before all that, I want to clarify some of the confusion on this thread between "frosted" and "crystallized" because there seems to be a lot of back and forth between these two points. "Frosted" is a surface quality trait that is normal to FUD parts and apparent immediately after cleaning/stripping of oils and being left to dry. In contrast "crystallization" as defined in the thread (and is the main issue) is the appearance of precipitates (ie. crystal formation) after a period of time. Here are pictures side-by-side to delineate between the two:

    Side-by-side.JPG
    Notice how the "crystallized" model has a substantially rougher surface quality than the "frosted" model with jagged edges that seem to be crystals forming on the surface. Also notice how the "crystallization" is more apparent on support facing planes (will be important later).

    Now, time for the meat of the issue. After investigating, all signs point to this "crystallization" being a material issue stemming from UV degradation. This is quite normal for many synthetic polymers (e.g. weathering of polypropylene rope), and FUD being a synthetic UV curable acrylic is also susceptible to it. Specifically, this degradation is caused by the photooxidation of free radicals (a byproduct of UV curing and UV exposure), which react with oxygen in the environment and break down the cross-links created during machine curing. This can explain why customers who left FUD parts in their plastic packaging did NOT experience the issue, from limited oxygen exposure in the bag.

    As of right now, the only suggestion I could give is to limit exposure to oxygen as that seems to be the main culprit behind the crystallization. Coating painted parts with an oil or using oil-based paint could help stay crystallization for a longer period, but seeing as photodegradation is a naturally occuring phenomenon, it would only do so much.

    I hope that this post was helpful in some way, at the very least to help shed light on the what we believe is happening chemically to the parts.

    I'll keep monitoring this thread to keep the conversation open!

    -Matt
     
  4. stannum
    stannum Well-Known Member
    How would that explain crystals appearing after painting? Some people apply multiple coats of paint and end with UV resistant varnish. The items are fully wrapped (specially after multiple coats) and light will hardly reach the underlaying material (some of the pigments are very opaque and resistant to UV themselves).
     
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  5. Cygnus3D
    Cygnus3D New Member
    An additional data point: Stuff I ordered and cleand in an ultrosonic cleaner in FXD in june 2015 has not shown crystallization, even though it's been exposed to air. Some of it's painted some of it's not. This was orderd in the EU if that helps.

    If this really is a property of the material (maybe only for some batches of your raw material?) I think it's a huge issue. "Do not use the items you ordered" is not a very good solution :(
     
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  6. Model_Monkey
    Model_Monkey Well-Known Member
    Deeply concerned.
     
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  7. Bathsheba
    Bathsheba Well-Known Member
    I've gotten a couple pieces of FUD and all have developed an irregular white powder coating within a few weeks. I don't do any postprocessing. I don't think I should have to, and I certainly can't advise my customers to -- they're not DIYers, they're expecting a finished product.

    I may not have gotten around to turning off FUD for the few products I ever turned it on for, but that's on my list. It would have been nice to offer translucent versions of some of my designs, but I can't consider this material suitable for any application where appearance matters.

    If that's how it is, ok, but I think the material description should say so, rather than showing photos of new parts with the implication that they'll be stable.
     
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  8. ibis2001
    ibis2001 New Member
    Hi there,

    I've started a thread in an austrian narrow gauge forum about the same problem.
    Text is german - change it to english with a little help of an online-translator if you wish - but there are definitely some interesting photographs to look at.

    http://www.schmalspur-modell.at/viewtopic.php?t=11676

    Enjoy, or better fear...

    Regards from Cologne
    Ingo
     
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  9. 00dwkr
    00dwkr Member
    Hi Ingo, thanks for keeping the thread alive.

    I have had the same experience: with item 'cleaned' (soap and water, I think), and then painted with acrylic.

    I will stop purchasing FUD from Shapeways until this gets sorted out.

    Thanks. Take care: Dan
     
  10. Model_Monkey
    Model_Monkey Well-Known Member
    SW, is there anything more you have learned to help customers experiencing the deterioration of FUD over time?

    Is FUD chemically stable?
     
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  11. MitchellJetten
    MitchellJetten Shapeways Employee CS Team
    Sorry for not replying.

    Behind the scenes we are actively investigating the issue and are doing tests.
    In addition we are in contact with 3DS to see if they can assist in resolving the issue as well.
     
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