Imidazole - epoxy catalyst

Discussion in 'Materials' started by MST3000, Mar 22, 2022.

Tags:
  1. MST3000
    Joined: Mar 2022
    Posts: 6
    Likes: 0, Points: 1
    Location: Caribbean

    MST3000 Junior Member

    Anyone has any experience with using Imidazole to cure (catalyze) epoxy, I've made a carbon mast and foils using it. Seems like a good candidate for epoxy hull builds given its very long pot-life, unlimited post-cure window and Tg higher than at cure!
     
  2. fallguy
    Joined: Dec 2016
    Posts: 6,068
    Likes: 1,214, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    What causes a post cure window to be limited?
     
  3. MST3000
    Joined: Mar 2022
    Posts: 6
    Likes: 0, Points: 1
    Location: Caribbean

    MST3000 Junior Member

    In general epoxies have about a maximum 5 day post cure window, no?

    Further the piece needs to be supported, because it becomes dimensionally unstable as the temp is raised, not the case with Imidazole.
     
  4. fallguy
    Joined: Dec 2016
    Posts: 6,068
    Likes: 1,214, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    I don't believe your statement is accurate at all.

    I mean no disrespect, but 2 stage post curing is done all the time afaik. The downside is the Tg may be less in 2 stage post cure, but how much? Probably not enough for boats to be worried about.

    An article supporting Tg being lower for secondary post cure.
    https://www.researchgate.net/profile/Steven-Nahm/post/Is_curing_temperature_dominate_glass_transition_temperature_in_SMP/attachment/5da863153843b093838c9360/AS:814974628794368@1571316501008/download/DMA+Presentation+(CFA).pdf


    An article mentioning any post cure beats none.

    Postcuring https://www.systemthree.com/blogs/epoxy-files/83509828-postcuring

    Supporting the piece is a certainty, but much more so if the post cure is immediate because it takes about a week for most room temp cure resins to get to a final cure that is glassier than rubbery.
     
  5. MST3000
    Joined: Mar 2022
    Posts: 6
    Likes: 0, Points: 1
    Location: Caribbean

    MST3000 Junior Member

    Please a little clarification, 2 stage post cure means: An initial room temp cure, then a post cure and then a second post cure? Sorry lack of basic understanding here.
     
  6. fallguy
    Joined: Dec 2016
    Posts: 6,068
    Likes: 1,214, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    I don't profess to be an expert. From my reading, I am interpreting a 2 stage cure to be ambient cure, followed by cooling from the exothermic reaction; the passage of time, and a 2nd cure to needed ppst cure temps.

    This is what I did for my boat hulls. The hulls were fully assembled; then post cured as an entire unit.

    How would I post cure hull seams that are built months later than the other components if post curing were limited to 5 days? I would only be able to cure each component, then be required to post cure periodically the entire hull. Virtually impossible to do perfectly..

    By my read of the technical paper, a 2 stage post cure is not as good as all done in a single stage, but far easier to control. Not as good means the Tg is lower, but by how much is not well understood (by me). As to whether it is significant versus the gains say of elongation of 8% (from 2 stage post cure), probably not..
     
  7. MST3000
    Joined: Mar 2022
    Posts: 6
    Likes: 0, Points: 1
    Location: Caribbean

    MST3000 Junior Member

    When epoxy is cured at room-temp, after the initial reaction a lot of cross-linking is left undone, and for the sake of argument, lets say 50% is achieved in 1 day. As time passes it will continue to cross-link but at a slower and slower rate until after weeks, say a further 15% is cross-linked. My understanding is that if it then post-cured, the existing cross-linked structure will only allow for a further 15% to cross-link. Whereas if it was post-cured after a couple of days, it can achieve near full cure (full cure is only achievable if cured at elevated temp initially, ie no-post curing)

    So what percentage of cure occurs initially, how much is further achieved at room-temp at time, how much more can be achieved if post-cured at a later time? Specifics, I have none.

    But I'm saying there IS a window, and the cross-linked structure that is created at a lower temperature DOES prevent a more cross-linked structure from being created at a higher temperature at a later time... Because Epoxies are thermoset, and heat will not allow the cross-links to re-order themselves once created.

    Imidazole is a catalyst, that is used at 4-10%, it causes the epoxy to cross link with itself. There is no window here, but much more importantly, the Tg is higher than at cure, so post curing can be done by just leaving it out in the sun, no oven, no controlled heating, no chance of warping, ever!

    All epoxies need higher than room-temp to "fully" cure, and time at that elevated temperature. The question of "fully" becomes how much cross-linking has been achieved.


    Handling Guide https://www.prosetepoxy.com/handling-guide/

    "
    3. Final Cure Phase
    In the final cure phase the epoxy mixture has cured to a solid state and, if not post-cured, will continue to cure over the next couple of weeks at room temperature. Post-curing at elevated temperatures will shorten the final cure phase of PRO-SET Epoxies, and is necessary for components requiring the best thermal properties.

    "
    There is much unsaid here too.
     
  8. fallguy
    Joined: Dec 2016
    Posts: 6,068
    Likes: 1,214, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    It would be nice if we had an expert weigh in..
     

  9. AndrewK
    Joined: Mar 2007
    Posts: 480
    Likes: 39, Points: 28, Legacy Rep: 344
    Location: Australia

    AndrewK Senior Member

    MST, I think you will find that you are one of a very small minority that has actually used Imidazole.
    I considered it many years ago because of the very long open time and higher ultimate mechanical properties.

    I decided against it as it would have required an elevated 60'C initial cure to be practical for me, also to attain the ultimate properties with my resin would have meant 24hr at 100'C initial cure or post cure.
    But even with a 60'C cure for both imidazole and slow amine hardener, imidazole product had a HDT of 90'C versus 70'C.

    Did you find the higher mix viscosity made it harder to wet out the reinforcement cloth?
     
    DogCavalry likes this.
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.