Polyester resin

[whateg01]

I'm getting ready to venture into carbon fiber laminations. Small project with few real constraints other than light weight. For what it is, fiberglass would be fine, but the person I'm doing the work for likes the look of carbon. I could probably do the first layer in carbon and the reinforcing layers in glass but I won't.

Anyway, I am using epoxy resin. But I got to wondering if polyester resin would work. There are several reasons not to use it with carbon, so I won't. But that me thinking about the fiberglass I've done in the past, and will do in the future.

Everybody says you shouldn't use polyester resin because of its hygroscopic properties. Yet one of the biggest industries to use polyester resin is boat building. Even the boat builders say out loud that it's fine to use for boats. So if it's so unsuitable for use where the thing will get wet, why is used so much there?

 

[cgrutt]

I'm a noob with glass but understand poly resin is hydroacopic only when uncured. Intermediate layers remain tacky which is actually good for bonding subsequent layers. They can add wax or cover final layer to allow full cure. I'm using vinylester resin for my boat repairs. Supposedly better than poly if you don't want epoxy.

 

[Firebrick43]

I'm getting ready to venture into carbon fiber laminations. Small project with few real constraints other than light weight. For what it is, fiberglass would be fine, but the person I'm doing the work for likes the look of carbon. I could probably do the first layer in carbon and the reinforcing layers in glass but I won't.

Anyway, I am using epoxy resin. But I got to wondering if polyester resin would work. There are several reasons not to use it with carbon, so I won't. But that me thinking about the fiberglass I've done in the past, and will do in the future.

Everybody says you shouldn't use polyester resin because of its hygroscopic properties. Yet one of the biggest industries to use polyester resin is boat building. Even the boat builders say out loud that it's fine to use for boats. So if it's so unsuitable for use where the thing will get wet, why is used so much there?

The biggest reason you cant use poly ester for carbon fiber that you want the look is its typically colored oddly (amber/red/even green) and it doesn't do well without gelcoat/paint to protect it from UV light

Second polyester does do ok in boats, especially if they are on lifts or set the majority of their life on trailers, is because its protected somewhat by gelcoat.

An isophthalic gel coat has pretty good resistance from water.

The majority of boat building resin is orthophthalic unfortunately and it does have somewhat lower water resistance to isophthalic resin.

The majority of visual centric carbon fiber layups is done with vinyl ester resins as they have physical properties between epoxy and the different flavors of poly resins and mid price as well. It usually is clear in appearance and most importantly is usually the best with resin infusion that is important as it allows dry lay up in the molds for superior visual appeal when finished.

Also it soaks into carbon fiber much better than any poly resin and probably even better than most epoxies. Real high strength carbon fiber is usually prepreg with resins that must be cured in an oven. The prepreg process uses machinery to force the resin into the cloth at the proper ratios and then its packaged and refrigerated till use.

They do make some bi colored fiberglass fabrics in nice twill patterns that emulates carbon fiber pretty good without its nasty wet out properties.

I'm a noob with glass but understand poly resin is hydroacopic only when uncured. Intermediate layers remain tacky which is actually good for bonding subsequent layers. They can add wax or cover final layer to allow full cure.

That isn't true. Orthophthalic resin is pretty hydroscopic even when well cured with wax. The main(and sometimes only) difference between a finishing and laminating resin is the addition of wax and it can be added to laminating resin on the last layer to make it finishing resin. Or you can coat with PVA or something washable to exclude oxygen and complete the cure.

I'm using vinylester resin for my boat repairs. Supposedly better than poly if you don't want epoxy.

That you are not wrong. Its a very good resin and many times I think I should use it over even isophthalic resin as its only about 20-30 dollars a gallon more, but a hell of a lot cheaper than epoxy.

If your glueing things together, like a wood boat coated in fiberglass, epoxy because of its adhesive qualities are still king.

 

[HeartBr8k1d]

I’ve had good results sourcing high-performance fabrics through Polyester, especially when I needed consistent stretch and fast-drying material for activewear lines. Nova Knitting’s options made it easier to match specific specs without a lot of back-and-forth, and their custom runs saved me from over-ordering. If you’re trying to fine-tune durability or fit, their warp-knit blends hold up well in testing.

 

[Beerhippie]

I thought poly resin for boats went away many years ago. "Boat pox" is a very real thing--ask a marine surveyor.

Gel coats crack with the slightest insult--and boats in the real work get a lot of insults.

I've been using epoxy resins (West Systems, to be precise) for boatwork since the '70s--often to repair poly with boat pox.

 

[whateg01]

I thought poly resin for boats went away many years ago. "Boat pox" is a very real thing--ask a marine surveyor.

Gel coats crack with the slightest insult--and boats in the real work get a lot of insults.

I've been using epoxy resins (West Systems, to be precise) for boatwork since the '70s--often to repair poly with boat pox.

I have watched a lot of YouTube videos of boats built with polyester resin. Seems vinylester is also popular

 

[senlow]

I thought poly resin for boats went away many years ago. "Boat pox" is a very real thing--ask a marine surveyor.

Gel coats crack with the slightest insult--and boats in the real work get a lot of insults.

I've been using epoxy resins (West Systems, to be precise) for boatwork since the '70s--often to repair poly with boat pox.

I'm a little late to the party. I've only been using West Systems since the early '80s. It's good stuff.

 

[gte718p]

The only reason not to use epoxy resin is cost. Of course there are a ton of different epoxy recipes, but I can't think of any use case where epoxy is not superior. When you are building something the size of a boat, the cost difference is not unsubstantial. When you are building 1000 boats, the difference is huge.

 

[Firebrick43]

The only reason not to use epoxy resin is cost. Of course there are a ton of different epoxy recipes, but I can't think of any use case where epoxy is not superior. When you are building something the size of a boat, the cost difference is not unsubstantial. When you are building 1000 boats, the difference is huge.

Vinyl ester resin is superior to epoxy for tanks, especially chemicals/hydrocarbons. Its also superior when doing dry layups in the mold with vacuum resin infusion compared to epoxy.

 

[gte718p]

Vinyl ester resin is superior to epoxy for tanks, especially chemicals/hydrocarbons. Its also superior when doing dry layups in the mold with vacuum resin infusion compared to epoxy.

They make epoxy resins specific to both applications. Both applications were used extensively in the aircraft industry, though I think they have gone almost exclusively to prepreg these days. I guess superior is situational. If you are 10x the price for a marginal gain, you are probably not actually superior.

 

[whateg01]

I don't do enough to really work about cost, but I know at least a couple YouTube videos I have watched said that the binders in fiberglass mat break down in polyester resin but not with epoxy. Is that true?

 

[Firebrick43]

They make epoxy resins specific to both applications. Both applications were used extensively in the aircraft industry, though I think they have gone almost exclusively to prepreg these days. I guess superior is situational. If you are 10x the price for a marginal gain, you are probably not actually superior.

From a pure chemical resistance I have seen epoxy made for fuel tanks fail with gasoline where the vinyl ester survived. Of course the epoxy may still have a structural advantage when the fuel tanks isn’t just a fuel tank and most aviation fuels don’t have ethanol in it to attack them.

 

[Firebrick43]

I don't do enough to really work about cost, but I know at least a couple YouTube videos I have watched said that the binders in fiberglass mat break down in polyester resin but not with epoxy. Is that true?

Yes, that is true. Most mats shouldn’t be used with epoxy. A few mat tapes are stitched together but I have only seen that a time or two.

If you are using epoxy for strength why would you want to use weaker mat anyway?

 

[gte718p]

Yes, that is true. Most mats shouldn’t be used with epoxy. A few mat tapes are stitched together but I have only seen that a time or two.

If you are using epoxy for strength why would you want to use weaker mat anyway?

you can use CSM with epoxy. The epoxy resin doesn't have styrene so the binder doesn't dissolve and it is harder to work with. Even wet, it doesn't want to drape and conform as much as CSM with the binder dissolved. However, the fibers still wet out, and the end result is the just as strong. There are binders designed for use with epoxy, they cost a little more but not much. West Systems did a bunch of test and demonstrations in the early 2000's that debunked the myth that you can't use epoxy systems with CSM. There are also CSM that are powder bound designed to work with epoxy.

 

[Firebrick43]

you can use CSM with epoxy. The epoxy resin doesn't have styrene so the binder doesn't dissolve and it is harder to work with. Even wet, it doesn't want to drape and conform as much as CSM with the binder dissolved. However, the fibers still wet out, and the end result is the just as strong. There are binders designed for use with epoxy, they cost a little more but not much. West Systems did a bunch of test and demonstrations in the early 2000's that debunked the myth that you can't use epoxy systems with CSM. There are also CSM that are powder bound designed to work with epoxy.

I didn’t say “can’t”. I said “shouldn’t”. Huge difference.

Even wet, it doesn't want to drape and conform as much as CSM with the binder dissolved.

Even you realize exactly why you shouldn’t. If it doesn’t conform as well in corners at worst you have enough resin to fill the voids from the stiff non conforming mat causing waste and low strength to weight ratios, at worst mat fibers try to return after wet out during cure and cause air pockets reducing strength.

And once again, why waste expensive epoxy for a low strength to weight ratio when E glass isn’t that much more and uses less epoxy. Mat will need 1.5 to 2 times the glasses weight in resin to wet out where weave will take a 50:50 resin/glass ratio although many times people get 55:45 in hand layups. Another reason one “shouldn’t” use epoxy with mat.