epoxy and polyester resin, can i put them together

more specifically, is there anything i can use to help the two resins adhere to each other. I don’t want to rely completely on a physical bond, although the few molds I’ve done with mixed resin, I haven’t had a problem with so far, i’d like to prevent anything from happening.

ALSO, If anyone can direct me to a more “composite” specific discussion group, i would be very grateful.

c’mon, there has to be a more composite specific message group that someone knows about…

Okay Jeremy, I’ll bite. But I must ask, what are you trying to do? Sounds like your making molds, yes? What are using them for? Vaccum forming, hand lay-up of fiberglass?

You say you’ve mixed the resins? Did you succeed? Are you using two-part, room temperature catalyzing epoxy resins (bisphenol A / Alaphatic amine compounds) or tetriary mixes? And the polyester-these are typically monomers with catalysts that would not doing anything to crosslink the epoxy molecule chemically. Are you trying to bond the resins together after they have catalyzed or when they are in liquid form?

Why even mix the two completely different chemical compounds? If you desire a certain property parameter, list your desires and I’ll see if I can direct to to an appropriate formulator or resource.

Epoxies are in of themselves a very versatile family of compounds. Whatever you are looking for in properties, an epoxy compound will most likely be superior to any polyester formulation.

So far as “composite” discussion groups, I can direct you there as well. Post your need so we can discuss further.

indeed, i’m making molds for motorcycle parts. relatively small in size in comparison to many composite uses. lets say an average size of 24x24, length and width to vary. highth to vary 2 inches to 18 inches lets say.

the reason i’m mixing (after curing) is to make up for my lack of technique. I want to laying the surface coat (epoxy) lay down a layer of cloth during tack to add surface strength. from there i need to wait for cure to add layers because i don’t want to create air pockets between the first layer of cloth and the rest of the glass, which is mat up to a thickness of about 3/8 of an inch with a final layer of cloth to control splinters from the mat.

that’s the basic construction currently.

my needs are as follows, i want to use the surface coat, it’s a 7:1 adtech surface coat epoxy resin, and use some kind of faster curing laminating resin. we’re currently using a 2:1. due to the tightness of our compentition I won’t mention the brand or kind of epoxy. i can’t chance it.

those are my current materials and construction as i know to explain them.

So you are using epoxy molds as a female cavity to make fiberglass layup parts that have an epoxy gel coat surface (your adtech material you mentioned, right?)

The epoxy or polyester you are using to wet and bind the fiberglass is your faster cure material, right? (the 2:1 “secret” stuff)

Well you will find that the polyester will delaminate along the epoxy surface boundary because you will get nothing except a physical bond. To get a chemically crosslinked bond, you’ll probably need to go an epoxy based material with a short pot life (10-20 minutes) and low viscosity (less than say, 50,000 cps). Since the wetting/binding epoxy won’t need to be filled, you should be able to get a low viscosity with no problem. The problem you will have is the fast kick. If you plan on mixing a large quantity (over, say 300g), you will find that excessive exotherm due to the fast catalyzation rate will cause excessive shrink and bubbling.

How thick a cross section are making with the faster cure material at one time? If its small, this fast won’t be a problem, it will be a requirment to make the epoxy kick and not stay tacky.

Do you need to find a resource for the epoxy, or do you just need guidelines on the process of making the part? I know a number of formulators, one on the US East coast whose chemist is a good friend. He and I have developed a number of compounds, tailor making them for different applications. I’m sure he, or any other formulator can give you what you need if you just tell them your lay up process requirements.

Note:
On Discovery Wings channel, a program called " A Plane is Born" had the guys doing just what you were describing, only they had a male form that they laid up fiberglass cloth and epoxy binder over. You may want to check it out.

yes we are using female molds for layup. the layup process is however: Primer, layup of two layers reenforcing mounting point and edges, using caposil mix for corners. For that though, i’m in the process of making compression molds for the mounting points and edges where delam is common and probable. The 2:1 epoxy resin is a slow cure, around 8 hours for tack and overnight for workable part. and a few days for proper cure. the part construction and materials is not what i need to change however, but FYI.

the cross section of poly is no more than one layer of 7oz twill cloth, which I should say, I haven’t done more than a few times because of the need to remain consistant with the molds, but have used a smaller parts without (so far) negative impact on construction or usability.

I would like to talk to someone about my needs and since you are the only one to help me here, perhaps we could correspond by email if that’s as easy for you as it is for me.

what is “CPS?”

the fast kick is what i’m looking for in certain instances. what i want to eliminate is air bubbles from the first few layers using rollers, which i’m familiar with. but with the current epoxy resin i’m using the kick time on the mold is hours for one layer of 14oz mat.

Jeremy

Why are you reinventing the wheel? Polyester/Fiberglas technology has been around for what, fifty, sixty years now.

Simplifiy your life an go polyester all the way; molds and parts.
The shrink rates will be the same, and there won’t be any chemical/mechanical interface bullshit, you can buy polyester at anyboat shop, automotive “bondo” is totally compatible, the list of pluses goes on.

Start here:

BTW, if you’re adding the catalyst to your polyester resin “by eye” that will be the root of yor short potlife problem. And the filler you’re using is Cab-o-sil…

I agree that that bond sounds like it’s going to delaminate sooner or later due to the lack of chemical bond…

if you’re dead-set on using 2 dissimular layers have you considered using a 3rd compound to facilitate the bond? I’m not following exactly what you’re trying to do, but I know in the past I’ve used either other epoxies or physical bonding agents to get resin layers to stick better.

There is no problem. It will work (with most epoxies). Think about it. You can adhere epoxy to epoxy after the first epoxy is cured. That is not a chemical bond. And you can adhere polyester resin to polyester resin after it’s cured (as long as it doesn’t have wax additive in it). It is wise to sand it a little before the second application of resin. Put your mind at ease and do a test panel and abuse it beyond what would be normal for your mold. If it doesn’t work, then it is probably the epoxy formula. At which point, just try a different epoxy.

There is no problem. It will work (with most epoxies). Think about it. You can adhere epoxy to epoxy after the first epoxy is cured. That is not a chemical bond. And you can adhere polyester resin to polyester resin after it’s cured (as long as it doesn’t have wax additive in it). It is wise to sand it a little before the second application of resin. Put your mind at ease and do a test panel and abuse it beyond what would be normal for your mold. If it doesn’t work, then it is probably the epoxy formula. At which point, just try a different epoxy.

Dear Guest,

The reason epoxies were made were to facilitate different preferences for composites. Since the shrinkage of polyester is a factor that we need to avoid, we use epoxy.
Epoxy does not shrink as much, unnoticeably in fact, and that’s why we use it. We need our mounting points to be within 1mm from factory original points. And also, if we were to make a poly mold, and later make a part for a plug, and make another poly mold, our mounting points would be off by… I’m guessing…. Somewhere around a half an inch by the end of the second mold. Epoxy on the other hand has a very small percentage of shrink. That’s just for the molds

As for the parts, if we made them out of polyester we wouldn’t be making better fitting longer lasting parts than our competition. Since we’re making motorcycle bodywork we need a construction that does not shatter on impact, and that will flex while sliding down the track at 120 mph.

As for the resin at “any boat shop,” and “automotive” bondo, that’s why we’re better than our competition. We don’t use shelf materials for our parts. We stay current with composite technology to keep our parts up to the standards we continually strive to achieve.

I’ve never complained about the short pot life of the polyester, my problem, should you choose to read is exactly the opposite. And we are not using only a mix of cabosil and resin. We use other stuff to facilitate a more flexible filler. Again, can’t go into details.


Dear Wintermute,

I am not dead set on using two dissimilar substrates. I am trying to achieve an effect, that effect being a faster drying first four layers. More specifically 20 minutes from mix to tack so I can use rollers and I don’t have to worry about moving the layers underneath each successive layer and disturbing the construction. I would like not to use polyester with epoxy, but that’s the only solution I’ve come up with due to my ignorance of the wide variety of resins. AFTER the first four layers, i’ll use the slow drying resin because it will not matter.

OK, now I understand what you’re trying to do better…

I’m not a resin expert myself, I use it occasionally for casting purposes and that’s all, but I think you are right that that’s the only way to acchive that effect.

In that case you might be stuck (if you’ll pardon the pun) hoping for a good mechanical bond (which may well be more than strong enough. or using another agent in between to try to get a better bond.