Hi,

I'm building an old 1/4 scale Discus (circa 1986 kit)
and the fuse is moulded using Polyester resin.

Can I use epoxy resin to glue the bulkhead/wing joiner
support in?

regards,
Chris
www.lsfaustralia.org.au
www.seat.lonnie.com.au

Dear Dr....

I wouldn't use epoxy to glue anything to polyester....use something polyester based...Selleys Polybond comes to mind....Its a thickened polyester (like toothpaste consistency) with a cream hardener for the formers....or use white silicon (bathroom stuff) for gluing in the servo trays etc which need a little give and flex in heavy landings

Hope that helps

Roachie
Who knows what sticks to blankets

Thanks Roachie; I found this too:

http://www.rcgroups.com/forums/showt...=2#post4561524

post #24 In the builder's experience; Epoxy adheres to cured Polyester.

Chris.

Originally Posted by DrFragnasty

post #24 In the builder's experience; Epoxy adheres to cured Polyester.

Chris.

I read that post and I don't believe thats what was said. All it talked about was whether epoxy would attack (degrade) polyester, and vice versa.

The fact that epoxy doesn't attack cured polyester is irrelevant to the question of whether it will bond. It won't. Polyester and epoxy are different matrices using different polymerization chemistry. The only similarity is that there is a "resin" part and a "catalyst" part.

Polyester resin is a mix of olefin esters and styrene, that is catalyzed with MEKP, a free radical initiator.

Epoxy resin is a long chain molecule with epoxide linkages at each end, that is catalyzed by a diamine.

If you want a good, secure bond between the parts and the fuse, use something that is polyester based. Epoxy may seem to adhere, but it will fail quickly under load once you go beyond the very meager surface adhesion between these two substances.

Jim Thomas

Good post Jim....Never heard the chemistry explained so sussinctly before...perhaps you could add your bit to the guide dude

Exactly as I've found....it doesnt bond it sticks for a while then at the first impact it lets go.....I was one of the first to build epoxy surfboards 30 years ago and made the mistake of using a polyester fin blank...lost the fin on the first big turn...

Silastic does stick/bond extremely well to polyester...I've been using it to hold servos and servo trays in for years..

Roachie
Still sticking to the blanket

Roachie,
I'm not surprised you lost the skeg on the first deep turn. The epoxy to polyester bond is lousy.

The answer to the chemistry part of my post is a PhD in Organic Chemistry plus 30 years in R&D. Some of it is actually relevant to the composites we play with. Glad it was informative.

JT

Originally Posted by jtlsf5

Polyester resin is a mix of olefin esters and styrene, that is catalyzed with MEKP, a free radical initiator.

Epoxy resin is a long chain molecule with epoxide linkages at each end, that is catalyzed by a diamine.

Jim Thomas

JT,

Dude, you are the MAN. I love to hear from people who know what they are talking about. It's what makes these forums worth sifting through.

Don.

P.S. Wish I had lines like that when I was dating. Trying to impress girls with sports talk never got me very far....

Originally Posted by dgliderguy

JT,

Dude, you are the MAN. I love to hear from people who know what they are talking about. It's what makes these forums worth sifting through.

Don.

P.S. Wish I had lines like that when I was dating. Trying to impress girls with sports talk never got me very far....

Don,
I've met Debbie, you did just fine, my friend. Missed you at the Otter, hoped you would stop by.
JT

She tolerates my hobby addiction, so I guess I did well where it really counts, eh?

I would like to have made the Otter, but it landed on top of our scale aerotow event in Skamokowa that weekend. Maybe next year!

d.

Hi Jim,

Trawling the 'net offers evidence that; yes, it can work for large surface areas by prepping the surface to reveal fibres, but in the context of my glider I'll go with Jim's experience and eliminate any doubts and use polyester resin.

Many thanks for the input Jim/ Roachie.

Chris.

NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO
Forget polyester
use Vinylester it will bond to polyester but has an epoxy matrix and will give much more service polyester is brittle and sucks water better than an sponge ,Thats why its rarely used in anything other than promoted polyester bog for fillers these days
SteveW

Huhhh....

Vinylester?....vat iss dis substance off vich you schpeek Schteven?

Not pulling the Old Secret Squirrels leg now are you?....I have to say I must defer to Jim here....What say you Jim?

Originally Posted by Roachie

Huhhh....

Vinylester?....vat iss dis substance off vich you schpeek Schteven?

Not pulling the Old Secret Squirrels leg now are you?....I have to say I must defer to Jim here....What say you Jim?

Der chemishcer hat gespeilen, und er hat sprecken dat polyester ist fur zie.

Polyester, vinylester, I believe we are speaking the same language but getting a bit technical. The difference is a minor one: vinylester is the monomer that when polymerized becomes polyester. Vinyl ester monomer resin is diluted with styrene to produce the "polyester resin" that is catalyzed to become polyester polymer. The additin of styrene to this mix gives it different properties than pure polyester, which is good to wear, but lousy as a structural material. QED.

One small word of caution, do not use the polyester finishing resin commonly found in hobby shops. This is meant for filling up the weave when cloth has already been bonded with laminating resing, and provides a nice sanding/finishing surface. It contains wax which allows it to cure 100% by keeping air away from the very surface of the resin (air will retard full cure).

You want laminating resin, which you will find at a marine supply store. This stuff will bond to cured or partially cured polyester. You will still want to rough up the surface you will bond to so there are some fibers for the new resin to adhere to.

JT

Lousy on structure ??? well I guess you must be mixing it incorrectly class 5 Vinyl ester is used for structural beams and air vents and water tanks in the mining industry so I guess you had better inform them . Plus the fact that all my Jarts are made using Vinyl ester . Quote
Vinylester resins are stronger than polyester resins and cheaper than epoxy resins. Vinylester resins utilize a polyester resin type of cross-linking molecules in the bonding process. Vinylester is a hybrid form of polyester resin which has been toughened with epoxy molecules within the main moleculer structure. Vinyester resins offer better resistance to moisture absorption than polyester resins but it's downside is in the use of liquid styrene to thin it out (not good to breath that stuff) and its sensitivity to atmospheric moisture and temperature. As vinylester resin ages, it becomes a different resin (due to it's continual curing as it ages) It is also known that vinylester resins bond very well to fiberglass, .
Polyester resin is the cheapest resin available in the marine industry and offers the poorest adhesion, has the highest water absorption, highest shrinkage, and high VOC's. Polyester resin is only compatible with fiberglass fibers and is best suited to building things that are not weight sensitive. It is also not tough and fractures easily. Polyesters tend to end up with micro-cracks and are tough to re-bond and suffer from osmotic blistering when untreated by an epoxy resin barrier to water. This is really cheap stuff.

SteveW quote un qoute

Originally Posted by steve wenban

Lousy on structure ??? well I guess you must be mixing it incorrectly class 5 Vinyl ester is used for structural beams and air vents and water tanks in the mining industry so I guess you had better inform them . Plus the fact that all my Jarts are made using Vinyl ester . Quote
Vinylester resins are stronger than polyester resins and cheaper than epoxy resins. Vinylester resins utilize a polyester resin type of cross-linking molecules in the bonding process. Vinylester is a hybrid form of polyester resin which has been toughened with epoxy molecules within the main moleculer structure. Vinyester resins offer better resistance to moisture absorption than polyester resins but it's downside is in the use of liquid styrene to thin it out (not good to breath that stuff) and its sensitivity to atmospheric moisture and temperature. As vinylester resin ages, it becomes a different resin (due to it's continual curing as it ages) It is also known that vinylester resins bond very well to fiberglass, .
Polyester resin is the cheapest resin available in the marine industry and offers the poorest adhesion, has the highest water absorption, highest shrinkage, and high VOC's. Polyester resin is only compatible with fiberglass fibers and is best suited to building things that are not weight sensitive. It is also not tough and fractures easily. Polyesters tend to end up with micro-cracks and are tough to re-bond and suffer from osmotic blistering when untreated by an epoxy resin barrier to water. This is really cheap stuff.

SteveW quote un qoute

Can't argue with cited authority. Just curious, but who's advertising pitch are you quoting? And if polyester was so lousy, why do boat and yacht manufacturers use it now as they have for decades?

I guess my 40 years of using polyester successfully in various applications doesn't count for much. And lets be very clear, inexpensive (cheap) doesn't mean bad, it just means its produced in very large (commercial) quantity, which benefits us little users that tend to be the proverbial drop in the bucket compared to commercial users. We benefit from the economies of scale.

There are always specialty blends being developed for various uses. Doesn't mean they are better or worse, just different.

I believe if you will do a little more research into polymers and polymer chemistry, you will find that styrene is more than a simple diluent. It is a structural component too. Why do you think polyester resins as used in the marine industry get hard and not supple like the polyester that is used in clothes manufacture? Answer, different co-monomers (like styrene) or no co-monomers.

JT