Absorbtion of Polyester resin by carbon uni

[Doc Martin]

we are vacuum bagging polyester resin and carbon unidirectional but the resin content is dropping to around 25% as it is all forced into the blanket the resin does not seem to be absorbed by the carbon and we are experiencing similair problems with 600g biax as well is this a common problem with polyester or because our resin is quite thin we are using crystic 272E to give us the working time we need as it is a large project we are working on

[War Whoop]

Carbon fiber usually is finished for epoxies and I have seen Vinyl ester compatible lately but Polyester?? Better check with the supplier.

[yokebutt]

Doc,
Since you've gone to the expense-level of carbon, (stringer caps, or something of that nature?) you might consider using a good quality vinylester instead, like Dow 8084 or 411-700, especially if it involves secondary bonding.

As for the resin content issue, you'll just have to do a lot of experiments to figure that one out, unidirectionals will "nest together" much better than wovens or CSM, (this is gonna be a lousy analogy, but bear with me, if you towel-dry your hair real good after showering it will feel damp, but if you comb it out it will feel wet again, not because you've added any water, but because the individual hairs are more closely nested together with less spaces between them that can hold water (with my luck, you're probably bald, but this is the best I can do on the fly!)) consider that in relation to the fact that CSM is usually used between layers of wovens or knits because it's inherently more resin-rich and thus used to help hold the more "structural" layers together in polyester layups.

Practical consideration; I'd encourage you to use a perforated release ply in the processing stack, it'll help limit the bleed-through and you won't have to pull 'til you're blue in the face to remove the saturated blanket.

I'm sorry if this posting raises more questions than it answers, I'm not all that well versed with words, especially in English.

What are you working on, anyway?

Good luck,
Parenthesisbutt.

[wet feet]

I too am puzzled that you have used carbon with polyester.Epoxy is more expensive but the difference must be small given the total cost of materials and labour for the project.I do not know anything about the particular resin you describe beyond the fact that it is manufactured by one of the best companies in the business.Why not ask their technical department for help?

[John ilett]

You have said that the resin is absorbed by the blanket?? I assume this is the breather layer and ask what type of release film you are using inbetween the laminate and breather.
Or explain your complete stack, eg carbon, peel ply, release film, breather and bag. Is this similar or are you maybe missing the release film so that there is no barrier to how much resin is bled out of the job?

[Doc Martin]

Sorry for the lack of replies but have been busy The project is the construction of a 69ft trimaran and we are all experienced builders but in using epoxy so we are having a few problems adapting the process to suit polyester which has been specified by the designer (we so wish he hadnt) we are using a standard stack ie cloth, peelply, release film, bleed blanket, bag. we have got the release film with the least holes we can but the resin seems so thin it just pours through we would like to change the resin but so far no joy are also concerned that we are not getting the carbon to absorb the resin as when we test a piece the broken fibres are very dry and still soft the main hull is being constructed from a kevlar and glass uni-directional cloth and we are assuming that we will encounter the same results with kevlar we have tried replacing the release film with a plastic sheet although this limits the resin flow it doesnt seem to increase the resin absorbtion we have also tried reducing the vacuum pressure but this mearly reduced the consolidation and could de laminate very easily just as a by the by does any body know the resin content on pre preg carbon

[John ilett]

This is strange, I know some styles of dry unidirectional carbon are kind of two layers and have seen others not wet this through properly thinking that vacuum would do this for them but not so. Maybe this is it?

Resin content for pre preg unidirectional carbon is usually around 35% and for cloths can be 40-45%.

[cyclops]

If the designer can specify Polyester, he can also specify the components that are going to give him his CALCULATED results. You are being asked to design a process which may not exist. Ask for the vendors and what he used on previous jobs to get his results. Designers specify, they do not generalize about how they want a structural part fabricated to meet finished specifications.

[yokebutt]

It's a rather curious set of symptoms you describe, a low viscosity resin will indeed squeeze out of a laminate easier than a thick one, but, by the same token, it should also saturate the fibers quite readily. In order to actually squeeze the fibers almost completely dry, I'd think you'll need a lot more than part of an atmosphere of pressure.

Thus, I would be inclined to suspect that perhaps something isn't quite right in the wet-out phase, you may even have a sizing compatibility issue, what technique do you use to apply the resin? I'm just throwing out a few loose ideas here, let me know how things turn out.

Yokebutt.

[John ilett]

That's right Yokebutt, I have never seen any particular problem with polyesters or thin resins. Typical pre pregs for example when processed with autoclaves are under 90-100 PSI (5 times regular vac only pressure of 14 PSI) and these do not bleed dry with perforated relase film.

[yokebutt]

Quite right, Mr Ilett, whenever questionable results occur, every step of the process has to be reviewed, In my experience, most of the time the questionable variable turns out to be me!

Yokebutt.

[cyclops]

I have a similar Q C problem. And I am perfect.