FUD FXD forming small crystals after time?

[SandyEggoJake]

@Lemosteam, as a customer oriented service provider, I suspect SW will eventually report out the findings ... but I do suspect the myriad of competitors (both service providers and material/technology innovators) will do so first.  The one group least likely to talk openly about the crystal composition (if it is an inherent material characteristic) is 3DS, as their business model is currently dependent on selling SR200 etc.  But you can bet this is an area for active R&D, and a rich field for patent development.  Yes, I already checked out the MSDS, but note it still redacts the ID of the 3DS proprietary monomers and polymers.

BTW, a bath or rinse of true distilled water will not leave any residual ... all H20 will (eventually) evaporate leaving zero precipitate. 

@peteski, Chemical trace analysis is widely available and common place now.  And I highly suspect that SW or rather 3DP has already gathered samples and determined the crystal composition.... otherwise SW would not have been able to rationally suggest a cause.  For me, the composition of this trace material is but an intellectual curiosity.  After all, like John, I've not yet seen it on my stuff nor a reliable method on how to induce it.  So getting sufficient quantity of a reliably pure sample to test is a far bigger challenge than sparking up the ol' mass spec.  But I just ordered some of John's lights and pass car details.  Perhaps an avoidance test with some sprues could be fun citizen science stuff... after all, my kid has a science fair each year.



 



 

[SandyEggoJake]

Wait!  Don't wipe those tippers!

If @Chris333 is willing to provide me ... oh say a 20 car of his frosted and excellent narrow gauge tipping mine cars  ...  with the understanding I'll never give them back (nor ever dust them) but put them to immediate revenue service on for my long intended South Bay Salt Works!  (Sparkles ain't a bug - its a feature!)



Seriously, this could be interesting....

Chris, you say this effect is more visible on dark painted surfaces.  But the pigment might also ******** the phenomena.  The common white pigment Ti02 is a highly effective UV absorber (think sun block).  So do you recall which specific primer and top coats you used on the items which produced the most sparkles?  Other details would also be interesting - age of print, time from print to paint, time post paint before the crystal bloom, exposure to UV sources (sun light, florescent or halogen lighting), etc.

[Chris333]

But I only have 16:
https://www.shapeways.com/product/5AB67KS8C/nn3-v-tipper-x-16?optionId=3702926
 

[Lemosteam]

@Chris333 , did you use any agitation in cleaning those parts or just a soak?  Just curious.

@SandyEggoJake thanks for the order!  I have lots of sprue material I can send yo you with a stamp.  PM if you want to share your address.  Also, I am still interested to know the composition of the powdery residue that can be scraped off easily.

[Chris333]

Those last tippers I showed were one of my first 3D items. Doubt I even heard of Bestine back then. So I probably soaked them in Acetone. They have also been sitting around the longest. Sorry it was around 5-6 years ago...

Now a days using Bestine I soak them and swirl the parts around every once in a while. Been wanting an ultrasonic cleaner, but I'm cheap. I do get wax build up in the bottom of used Bestine so I now it is doing something.

[SandyEggoJake]

Yep, Acetone isn't compatible with SR200.  That is likely part of the issue - if not the cause.  Recall what primer and paint?

Been wanting an ultrasonic cleaner, but I'm cheap.

Wife flipped when she found I borrowed hers ... so (also being cheap) I just ordered a CHIna! special for ~$5 bucks with shipping.

[SandyEggoJake]

@Chris333  Any sparkles showing on items for which you are confident you didn't use Acetone? 

[SandyEggoJake]

One alt working hypothesis (quite unrelated to the UV breakdown theory) is these crystals are 2-hydroxyethyl methacrylate a component in pHEMA.  Related to the chemistry of the Triethylene glycol dimethacrylate ester which constitutes a major portion of SR200.   Best method to ID such is GC & NMR.

pHEMA is very hydroscopic (used to make contact lenses) and thus will pull water out of the air, but when dried will crystallize and expand.  SW apparently uses a water base to clean oils off parts right before they ship them.  Note the case on someone moving to AZ and found the crystals after storage  - perhaps a hotter / drier environment.  Solvents like n-Heptane (Bestine) actually causes it the precipitate out of an aqueous solution (and likely to dry out such forcing recrystalization).

@Chris333, you stated your layout is in your basement?  Do you have humidity / moisture in your basement in the winter & spring that goes away in the summer (and you notice this bloom when it is dry)?  It there much temp fluctuation also? 

Also, do these crystals show true iridescence... a color change when you change the view angle.   

http://pubs.acs.org/doi/10.1021/j100548a009

[Chris333]

Wish I could be more help with the "exactly what did you do to clean the model"      Now I soak everything in Bestine or Beacon:
http://www.beaconadhesives.com/beacon-adhesives-launches-rubber-cement-solventthinner/

Usually the first thing I do is spray it with primer so I can see what I have. Then I will sand down any lines, scrape areas with a flat screw driver and stuff like that. The black tippers just got cheap 99 cent flat black spray. Some times between sanding I *might* do a quick dip in Acetone since it evaporates quick. No soaking for days though, it will warp the parts.

As for my basement the temp doesn't change much and right now it is 45% humidity down there. I don't get water, but it could be a little damp. In the winter time I run humidifiers upstairs and was just looking into one that goes on the furnace. I would say it is more humid in the summer time.

The green speeder is showed was just designed in June so I'd say nothing much in the basement has changed since then.

The specks do change color like pink, blue, purple. In my first photo a few of the specs show up colored.

[narrowminded]

I have a set of Chris's small tipper cars for experimenting and painted one.  It was washed in an ultrasonic cleaner with mineral spirits (didn't have Bestine) and dishsoap.  Rinsed with tap water, also in the ultrasonic cleaner.  It has visible sparkling.  It was painted about a year ago.

[narrowminded]

... it was brush painted with flat black, inexpensive (cheap), acrylic enamel with no primer.

[Chris333]

I took a tipper last night and cleaned the sparkles off with a brush. It works, but it is very hard to get into all the small spaces and a I broke off a small post.

So they can be cleaned off.

[SandyEggoJake]

>I would say it is more humid in the summer time.

Actually, if it is a pHEMA related hydroscopic cmpd, that makes more sense.  Catching up on pHEMA, it's actually being used (or at least studied) as the motive material in printed humidity sensors, apparently expanding with the addition of -OH from atmospheric H2O and contracting again when dry.  So a purified cmpd in this family might bloom as a crystal that expands out of surfaces during periods of humidity.   

Of course all this could be a red herring....

BTW, I'm losing a bit of faith the crystals are 2-hydroxyethyl methacrylate specifically.  But I think we're on the right path, as this fits with a SW observation that crystallization tends to be more pronounced on surfaces that contacted the the wax support (and clearly differentiates this from the frosted effect, also seen in this support contact regions), as well as not seen on parts keep in a bag (not fully buying the SW observation that low o2 is sufficient or necessary to prevent the bloom, for the contrapositive doesn't explain why many others haven't observed this phenomena). 

Also, this study has me also questioning if Bestine (n-heptane) might be too harsh to be an ideal wax remover.  You see, it seems FUD actually isn't a single compound, but an admixture.  The core of the lattice is a urethane dimethacrylate polymer, which results in a white brittle structure and undergoes more polymerization shrinkage than might be desired.  So triethylene glycol dimethacrylate is added to the soup, which improves viscosity but also polymerizes and gets added into the lattice (perhaps akin to muscle on bone?) resulting an a smoother appearance but also less brittle part.  So this whitening effect of acetone and other harsh solvents might be actually stripping the TEG-DMA out of the FUD, leaving the a more brittle urethane shape with more pronounced frosting (not crystals).  The crystals come later... but perhaps also via the solvent exposure, which might convert the TEG-DMA to another compound, but leaving some as a hydroscopically unstable byproduct which in the right conditions leaching out to form these iridescent crystals.  And of course, lets not forget the SR200 has proprietary photoinitiators (perhaps these are the so called free radicals?) which remain as trace compounds in the FUD, and under the right conditions might likewise be remolding the lattice.   

Anyway, all this has been a (LACK OF REAL) thought experiment ... by one who has never worked in this particular corner of chemistry.  But I've zipped some technical questions over the SW and 3DS and will update here if I hear anything more.

Without an adequate fleet of blooming items from which to harvest the sample, getting an adequately pure and significant sample to run both GC & NMR would be a challenge... but it does get interesting if that cut of tippers comes with z gauge wheels and Plymouth to haul them around! 
   

[SandyEggoJake]

Some  details from 3DS on FUD (SR200)... including post processing and finishing recommendation  ... can be found on page 28-32 of the following.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&ved=0ahUKEwiq_LbxjaTXAhXl64MKHXp6DZEQFgg6MAM&url=http%3A%2F%2Finfocenter.3dsystems.com%2Fproduct-library%2Fsystem%2Ffiles%2Flegacy%2F3DSCentral%2520-%2520Legacy%2520Products%2FProJet%25203500%2520Series%2FCustomer%2FPost-Processing%2520the%2520Parts%2F2107_VisiJet%2520Material%2520and%2520Post%2520Processing%2520Guide.pdf&usg=AOvVaw18AKCPTN2PPUYEDYYyb0ge

[Chris333]

Corn oil?