Heat curing prepreg, cumulative?

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#1

My application is bonding prepreg tow (formulated with EPON828) to wood that has already been pre-bent to a specific geometry with heat, about 115C. The tow manufacturer calls for 135C for 4 hours, which would obviously cause my wood to relax and lose its shape if I were to apply the pregreg to the wood and then heat cure. I need to cure the prepreg once applied to the wood in some other fashion other than heating the whole piece of wood for a long time.

My question is, are there issues with applying multiple passes of high heat, with cool cycles in between? Would the prepreg eventually cure cumulatively from short passes of high heat?

#2

Possibly yes, depending on what you do with the heat and if activation energy of the resin is hit, etc but one of the key things that may happen is the resin will not flow properly and you will get a lot of voids. Not a good idea and expensive i think.
My advice; get a lower temperature curing pre-preg or is there a reason you’re using that one?

#3

you need to achieve a minimum temp for a minimum amount of time for the epoxy to cross link. Usually the resins have a few possible recipes to cure. Some will do a say a 1-2hours at 250deg or 8 hours at 200 degrees. Or something of that nature, the resin tds should have that information. If not then you should call the manufacturer and ask what they think about your problem, they might have advice. Or possible change to a different resin system.

You might be able to do a lower temp cure and get the resin to harden, but this doesn’t mean you’ve reached the full specified properties of the resin. There is usually a minimum temp for cure/post cure that will give you the full specified properties of the resin.

As Findhan said, changing resins might be the answer. Or you can rethink your process. Make a mold, cure the carbon, then bond it to the wood.

#4

Thanks for the replies, which agree with my experimentation over the intervening time. I did not get good results in testing, and have abandoned the idea. I have gone to a wet layup with a room temp cure epoxy. It’s more messy, but a good cure is paramount. Making a metal mold, heat curing, and then bonding to the surface is a viable idea, but I will try it some other time in the future.