Oxygen Absorber at 200-350 deg F For Curing Photopolymer

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Discussion Overview

The discussion centers on the challenges of curing a photopolymer in an anoxic atmosphere at high temperatures (200-350 deg F) to prevent interference with a gypsum-based investment during casting. Participants explore various methods to absorb oxygen and maintain the integrity of the polymer during the curing process.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant proposes using aluminum foil with charcoal to absorb oxygen during the curing process but questions the reactivity of carbon at high temperatures.
  • Another participant suggests alternatives to carbon, such as nitrogen or dry ice, to create an oxygen-free environment, while also raising concerns about the potential for fire from carbon reactions.
  • A participant mentions using steel foil with charcoal at higher temperatures to prevent oxidation, indicating that fire is not a concern in their commercial burnout oven.
  • There is a suggestion to bathe the models in argon before sealing them in foil to achieve a near oxygenless environment, although this may not be a sustainable long-term solution.
  • Surface treatments post-curing are discussed, with concerns about their effectiveness and the potential for detail loss in the models.
  • One participant expresses interest in the possibility of electroplating a polymer as a solution to surface treatment challenges.

Areas of Agreement / Disagreement

Participants express differing views on the best method to absorb oxygen during the curing process, with no consensus on the optimal approach. Concerns about fire risks and surface treatment effectiveness also remain contested.

Contextual Notes

Participants acknowledge limitations in their proposed methods, including the reactivity of materials at high temperatures and the challenges of applying surface treatments evenly without compromising model detail.

EricM81
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Basic Question:

I am trying to heat cure a photopolymer for a couple of hours at 350 deg F in an anoxic atmosphere. My idea was to seal the part in aluminum foil with charcoal to absorb the oxygen, but was not sure that the carbon and oxygen would react at that temperature.

Extra Background Info For The Extra Curious:

I'm working with a 3D printer that uses a light cured polymer (B9 Creator). 3D models are sliced into layers and projected one at a time into a vat of photopolymer. It starts the reaction and cures the model just enough to make it solid. Any more and the light would bleed into the next layer. Once a part is printed, it's washed with IPA to remove liquid polymer and then fully cured. The cured model is placed in a gypsum based investment and the polymer is burned out of the mold for casting.

Problem:

The polymer is reacting with the investment. Gypsum based investment utilizes a complex chemical reaction. Normally, water is mixed with the powder and a slurry is poured into the mold. The water and binder harden the slurry into a solid. The next reaction completes the hardening. If you heat the model at a specific rate, water is expelled and the cristobalite expands at a rate that maintains dimensional stability.

One way that the polymer interferes with the investment is through thermal expansion. If you fully cure the polymer with a UV light box, the model will undergo thermal expansion. Thicker cross sections will break down the investment just as the cristobalite begins to expand.

The other way it interferes is if you opt to heat cure the model. Heat will complete the reaction initiated by light and allow the model to undergo thermal expansion prior to being in the investment. However, heat cured models will interfere with the investment's chemical reaction leaving a rough surface finish.

Recently, someone tried curing the models by heating submersed models in baby oil (microwave). The results are reportedly perfected. My theory is that the heat plus anoxic environment are making the model thermally and chemically inert. I would like to test this by sealing them with aluminium foil and oven curing them in an anoxic atmosphere.
 
Thanks Greg. To phrase as simple as possible, at what temperature does carbon react with and absorb oxygen?
 
I don't know about the carbon, but that would not be my first approach. A reaction would also heat up the carbon, with the risk of starting a fire.

If oxygen is the problem: do you have access to nitrogen, dry ice or something else you can use to flush your heat chamber?
EricM81 said:
However, heat cured models will interfere with the investment's chemical reaction leaving a rough surface finish.
What about some special treatment of the surface after curing?
 
At higher temps to prevent oxidation, we use a kind of steel foil with charcoal to absorb oxygen, which is why it was my first thought for doing it at 350 def F with aluminium foil.

Fire is not a problem. This is in a commercial burnout oven that's made to allow airflow and burn out all of the carbon in the chamber.

I can bathe it in argon while I seal the foil. That will give me a near oxygenless environment for testing, but if successful it's not a great long term solution.

Surface treatments have varying levels of success. Plus they're hard to apply in a thin layer evenly without pooling. You tend to lose detail, sub 1mm holes get filled in, etc. If only you could electroplate a polymer.