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Additives in SLA

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I have a few chemical questions about my Stereolithography (SLA) printer. As best I understand it, my resin liquid is really just a bunch of Monomers and Oligomers and Photoinitiators.

Question 1: what happens when the Photoinitiator is exposed to uv light and why does this help the monomers/oligomers connect together?

Question 2: When I add additives to my resin (pigments, other molecules, etc) does the additive essentially get tangled up in the long cured polymer strands OR are the additives forming covalent bonds with monomers/oligomers?

Question 3: it seems like most people just mix in additives with their resin and then use it immediately. Doesn't it make sense to try to get the uncured resin to form covalent bonds with the additive? As long as I pick a molecule that has multiple valance electrons and I mix it well with my resin, how can I cause the monomers/oligomers to form covalent bonds with the additive molecule?

If you could share any articles or websites that go into details about this topic and the chemical reaction side of SLA, that would be awesome.

Thank you!

1. The photoinitiator makes radicals during irradiation which propagate from monomer/oligomer to monomer/oligomer making a network

2. Its getting tangled up

3. No, the resin is not binding to the additive, it is simply dissolving it or if it is insoluble (like a pigment) then it is wetting the surface.

Look up free radical polymerization of acrylates. Your additives usually do not contain free radically polymerizable groups on them.

Hi wildfyr,

Thank you for your response.

Ok, so let's take for example phosphate, which (I think) is a negatively charged radical.  If I mix in phosphate as my additive in my resin, what will happen?

I realize that this is a simple question with probably a really complex answer, but I am trying to learn more about this topic (specifically, the chemical reactions that occur).

My thought is that if I mix in the phosphate with the monomers, that the phosphate will react with some of the monomers and bond to the monomer (creat a bond with the monomer and phosphorus, release some oxygen byproduct). Then, when I apply UV light and polymerization occurs, then my polymer chains will have phosphorus atoms bonded in it.

Does this make sense or am I way off base

Thank you,

Phosphate is not a radical. Its an anionic salt.

James, I think you need to be starting at square 1 with organic chemistry, because you are just throwing out word salads of organic chemistry terms that do not have much relation to reality. So yes, you are way off base.

What is a bond? How are radicals formed? How does UV light break a bond? Which bonds does UV light tend to break? How does phosphorous like to make bonds?

A 2 semester college level course in organic chemistry would teach these things, but they are nigh impossible to learn with "A little bit of this and that" reading websites and watching youtube.

There are youtube series that teach the entirety of organic chemistry, and if you have patience it is possible to learn it at that level. It takes months.

Thank you for your honesty.

Do you have any recommendations for organic chemistry textbooks?

Thanks again,


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