I' m currently making tensile test samples for Unidirectional (UD) Prepreg. Therefore, I need to fabricate a 1mm thick unidirectional sheet. I used two glass plates that sandwich five layers of UD Prepreg and are vacuum baged and cured in the Prepreg oven at 100°C (see attached pic). The two glass plates were treated with six layers of Easylease coated with a 20min. separation between each coating. However, I still have the problem that the Prepreg sticks to the glass. I cannot manage to take the Prepreg sheet off the glass without braking the glass or the prepreg sheet (see attached pic). I tired this several times already. Any Idea how to resolve this? What about trying to use PVA or wax as a release agent, instead of Easylease?

Looking forward fot some help

Kind regards

Pier

Yeh it sounds like you're going about it the right way. The one thing I might point out is that you may be going a little heavy handed with it, which is a common cause of failure. Over-application is actually detrimental, as if the film you are applying is so wet that it can form a droplet and bead up then it will do that rather than cling to the mould surface - something that is especially true for glass surfaces because glass already has quite a low surface energy. You want to be applying just enough to leave a film on the surface, but not so much that it forms streaks behind the cloth... What I do is I actually cut the solvent application wipes into 8 strips, and then use them individually. This way they can absorb less material, so it isn't as easy to over do the application. For such a small surface, I would also suggest only applying the Easylease to one area of the cloth rather than the three that you have been doing. Give it another try using this method and see if it works better. 

Another reason for doing the 8 strips is you shouldn't reuse the same piece of cloth for each application of release agent, you should throw each piece away and use a new piece for the next layer. What happens is the release agent that remains on the cloth partially cures, and then when you apply more to it, the solvents partially dissolve it and transfer to your tool surface as a greasy film. In practise, this shouldn't really cause any problems other than a bit of a streaky surface that will transfer to your finished part - but it is something to avoid regardless.


You can also do a quick 'tape test' prior to applying any resins which should indicate whether the release agent is working. If you place a piece of masking tape on the glass before you apply any release agent and peel it off, you should feel a fair bit of resistance. Then apply your release agent, and before you apply any pre-pregs or resins, place another piece of masking tape on the surface. If the release agent is working, you should find the masking tape will come away with very little effort, and in fact it may not stick to the surface at all and simply curl up. If it doesn't feel much different to before you applied the release agent then it's a pretty safe bet that the release is going to fail. 

+x

 

Hanaldo - 1/2/2018 2:36:31 AM

Yeh it sounds like you're going about it the right way. The one thing I might point out is that you may be going a little heavy handed with it, which is a common cause of failure. Over-application is actually detrimental, as if the film you are applying is so wet that it can form a droplet and bead up then it will do that rather than cling to the mould surface - something that is especially true for glass surfaces because glass already has quite a low surface energy. You want to be applying just enough to leave a film on the surface, but not so much that it forms streaks behind the cloth... What I do is I actually cut the solvent application wipes into 8 strips, and then use them individually. This way they can absorb less material, so it isn't as easy to over do the application. For such a small surface, I would also suggest only applying the Easylease to one area of the cloth rather than the three that you have been doing. Give it another try using this method and see if it works better. 

Another reason for doing the 8 strips is you shouldn't reuse the same piece of cloth for each application of release agent, you should throw each piece away and use a new piece for the next layer. What happens is the release agent that remains on the cloth partially cures, and then when you apply more to it, the solvents partially dissolve it and transfer to your tool surface as a greasy film. In practise, this shouldn't really cause any problems other than a bit of a streaky surface that will transfer to your finished part - but it is something to avoid regardless.


You can also do a quick 'tape test' prior to applying any resins which should indicate whether the release agent is working. If you place a piece of masking tape on the glass before you apply any release agent and peel it off, you should feel a fair bit of resistance. Then apply your release agent, and before you apply any pre-pregs or resins, place another piece of masking tape on the surface. If the release agent is working, you should find the masking tape will come away with very little effort, and in fact it may not stick to the surface at all and simply curl up. If it doesn't feel much different to before you applied the release agent then it's a pretty safe bet that the release is going to fail. 

I will try to use eight separate strips and try the process again...
I can confirm that I had streaks left behind on the glass when applying easylease and that I reused a lint free cloth that was used and soaked before.
I also want to point to out, that the easylease layer was visible before vacuum bagging and that it disappeared compleately after processing the prepreg layup in the oven. It is, as if the glass would have soaked it up, the film evaporated or diffused into the glass? Thank you for helping out once more.