Etching / Redox Reaction & Thermoplastic Polyurethane?
  • Hi there,

    I’m trying to etch some copper to be a circuit. The etchant is sodium persulfate, Na2S2O8.  It’s diluted 25% into water.

    For the resist, I want to use 3d printed flexible filament, NinjaFlex, which is a thermoplastic polyurethane.

    However, I’m not getting very far on figuring out what the possible interactions would be with this material and Na2S2O8 (aq), CuSO4 (aq), Na2SO4 (aq).

    What I tried so far was to ask the maker of the filament what would happen. Since sodium persulfate is a strong oxidizer, they do not recommend it. (But they didn't explain why)

    I tried searching for answers and clues, but I’m probably not searching for the right topic.

    From my imagination, I think that this experiment could turn out poorly if the thermoplastic polyrethane (after it reacts with the products) becomes oxidised to a harmful compound, or if it’s an exothermic reaction and releases a harmful gas. I think the gas scenario would be unlikely since I’m not adding heat to the reaction- it’s about 18 deg C. It would take more energy... 

    But I don’t really know. Do you have any ideas???

    How would one figure out how this organic chemical reacts with these chemicals?

    Thanks for taking the time to read my weird question and any help you can lend!

  • My experience with most polyurethanes is that very little can affect them in a serious way. Solvents that destroy plastics have very little effect. I don't know Ninjaflex or other TPEs in this context, but my instinct would be that *if* you can get good adhesion to the copper, it will resist etching. It should be much, much less active in interacting with the acid than the copper is. However, what I would be primarily concerned about is whether and how you can remove it from the board after etching. If you can find a way-- which might be as simple as melting it off -- i would go ahead and try, with excellent ventillation. Even the acid fumes alone require that.
  • Add on: assuming that etching goes well, the properties of the ninjaflex will likely be degraded on its surfaces. That may be why it isn't recommended.
  • Thanks for answering my question and the info about TPEs! Good point about removing the NinjaFlex afterwards, not really sure how to do this yet. Was thinking about using acetone (in a well ventilated area). Just the heat from soldering makes the board (Pyralux) a little warpy and melty on the other side.

    It will be cool to see if someone does a similar project with an etch resist pen and the WaterColorBot. Or even the EggBot with a copper egg. That would be nifty.

    Thanks again!