Does direct sunlight....

Discussion in 'Materials' started by Meanz Beanz, Aug 25, 2008.

  1. Meanz Beanz
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    Meanz Beanz Boom Doom Gloom Boom

    ...have a roll in curing epoxy and/or polyester resin. Aside from the heat factor.... say you have two epoxy brews at 12 degrees C one in sunlight and one in the shed, aside from the long slow cure at that temp would one go off faster than the other?

    You see its these light triggered catalysts that are in resins that are in use around the place, they have got me wondering... is the light triggering catalysation (sp?) a completely new "design feature" or have they just refined and exploited a natural tendency inherent in all resins?

    Any chemists out there that know bout this stuff?

    Cheers
    MBz
     
  2. the1much
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    the1much hippie dreams

    alright,,,,confused,,hehe,,,,,they say "light" makes it caty? ,, i know in regular stuff the reason they say not direct sunlight is because of the heat,,,,,does this stuff work under any "light" or jus uv?
     
  3. Meanz Beanz
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    Meanz Beanz Boom Doom Gloom Boom

    There are resins that have the catalyst pre mixed and it is set off by white light. They use them in dentistry for white fillings for example... I have been told of, but have not used, a polyester resin that surf board makers use that needs to be put in the sun for the reaction to start (I think thats a post mix catalyst, and I think its the catalyst thats special not the resin)... anyway they can mix it, work for as long as they need, then wheel the thing out into the sun and away she goes... sounds neat to me, anyway I was just wondering about the whole effect of light on resins thing and if it was purely by design or if it was inherent to some degree that light as apposed to heat helps catalysation (sp?).
     
  4. Meanz Beanz
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    Meanz Beanz Boom Doom Gloom Boom

    I don't know for sure, I do know that certain specialist products use "white light"... so I guess its spectrum related somehow? Dunno bout the polyester one, was hoping to be told....

    well told more that the usual get s.........ed! :D :p

    I was told that the reason for the white light was penetration... its better, better than what... I dunno.
     
  5. the1much
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    the1much hippie dreams

    time to try,,,,do a small piece in the closet,,, and 1 outside when the temp is about the same as your "dark spot",,,,i think i like the idea of "all that working time",,,and then jus wheeling it out.
     
  6. Meanz Beanz
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    Meanz Beanz Boom Doom Gloom Boom

    http://www.fiberglasssupply.com/Product_Catalog/Polyester_Resins/polyester_resins.html

    I don't know if its stronger/weaker or what...?!
     
  7. tinhorn
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    tinhorn Senior Member

    Sunlight (mainly for the UV rays) is awesome for getting your polyester or vinyl ester layup to kick quickly, or to cure a part when it appears your catalyst level was too low for the temperature of the shop. (Also when you fear your gelcoat may "alligator" from being too thin or catalyzed too low.) Heat without sunlight will accomplish the same thing, but usually a bit slower. Heat AND sunlight may cause the part to get too hot while curing.

    That's the case with resins I used decades ago. Sounds like these young whippersnappers have taken UV curing to the next level.

    (I once operated in a tiny and well-insulated shop. I installed a 5000-watt electric house furnace and a huge, ugly air conditioner. Man, in three minutes I could have that shop any temperature I wanted.)
     
  8. Meanz Beanz
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    Meanz Beanz Boom Doom Gloom Boom

    Thanks Tinny,

    So there's summin in the "light" thing then!

    I was hoping we get a chemist type to say what & why...

    I was doing some flow coating the other day some in the shed and some outside. I hit gel time allot quicker outside and it is only weak winter sun down here, hardly a temp difference to talk about at all.
     
  9. Petros
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    Petros Senior Member

    heat will always cause chemical reactions to go faster. This is a well known fact by all chemists. I am an engineer, but my sister is a Phd chemist and she told me this once when discussion chemical processes (pressure also works the same way heat does, speeds reactions).

    I suspect a clear resin will absorb and hold sunlight, and speed the reaction.

    There are some chemical reactions that are increased by UV light. But UV light can also cause a break down in certain certain chemical bonds, it can be used for example to weaken glue bonds to disassemble a glue joint.

    So heat and pressure will always be beneficial to speeding a reactions, but UV light will depend on the type of materials and reactions you are dealing with.
     
  10. Meanz Beanz
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    Meanz Beanz Boom Doom Gloom Boom

    We all know about heat, the light element is what I was curious about... so yes, what of polyester and epoxy ---> does it really make a blind bit of difference? Anecdotally at least it seems there might be something in it for polyester.
     
  11. PAR
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    PAR Yacht Designer/Builder

    Light doesn't cause the reaction in polyester, vinylester or epoxy resin systems, though it does affect the process. Many things also can have an affect on the cure process, humidity, ambient temperature, particulate density, type of light, etc.

    The same is true of heat with the three basic resin systems we use.

    This said there are chemical combinations that do react to light (and heat), sometimes to very specific wave forms.

    Generally, the polyesters and vinylester resins are "catalyzed", by this the hardener increases the cure rate, but doesn't become part of (typically consumed by) the finished molecule. Epoxy on the other hand is "activated", whereas the reaction takes place as a result of the introduction of the hardener and becomes part of the resulting new molecule.

    These reactions will take place with or without the presence of light. They will also take place in a fairly wide range of temperatures, though there are clearly limits, to how low or high the temperatures can be for successful cures.
     
  12. ondarvr
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    ondarvr Senior Member

    UV light can speed the cure of a polyester resin already catalyzed with MEKP, but alone won't cure it well unless a UV initiator is used. We make products for this type of use, but the logistics of using them in production can be difficult to over come. On flat panels made with thin laminates you can get a very good and even cure, the problem is that when the laminate is not at 90*s to the light source the cure is slower and if the light doesn't hit that area of the laminate at all then the cure can be very slow. When a laminte cures at different rates over it's surface it can become distorted or may be weakened. As the laminate gets thicker less UV light will penetrate to the other side resulting in a poor cure. In gel coats or pigmented resin the light will be blocked by the pigments, so thickness is even more of a limiting factor. Another issue is the cost of the UV lights, it can cost more than $100,000 for a light booth to cure laminates and to judge the amount of time needed to cure the resin you need to measure the energy output of that exact light bulb and over time the output will be reduced until the light needs to be replaced.
     

  13. Meanz Beanz
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    Meanz Beanz Boom Doom Gloom Boom

    Thanks... :D
     
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