scootz
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| posted on 14/8/08 at 11:21 AM |
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Polyester or Epoxy Resin
Is there a difference?
It's to use as a bonding agent.
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balidey
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| posted on 14/8/08 at 11:28 AM |
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epoxy is much stronger, but its nasty stuff if you get it on your skin, so wear PPE. It also stinks.
As to which is best, it depends on the application its being used in
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smart51
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| posted on 14/8/08 at 11:48 AM |
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If you think epoxy stinks, you haven't smelled polyester. epoxy is the low odour alternative.
epoxy is generally thought of as better. I believe it is less brittle. It costs more and smells less. It is more sensitive to mixing the right
quantities as the two parts react with each other to form the polymer.
polyester is fully mixed bar the catalyst. 2 - 3 % is needed to cure but it is not too sensitive. slightly less than 2% catalyst but will mixed will
probably still cure but more slowly. a bit over 3% might cure too quick;y but will still go off. It can be bought almost anywhere (Halfords etc).
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Delinquent
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| posted on 14/8/08 at 11:48 AM |
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quote:
Originally posted by balideyIt also stinks.
Doesn't smell anywhere near as much as polyester!!
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David Jenkins
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| posted on 14/8/08 at 12:03 PM |
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As balidey says, keep epoxy off your skin. It may not affect you, or may not for a very long time, or you might get a reaction almost immediately.
Once you're sensitised to it, you may be unable to touch anything made from, or containing, epoxy resin ever again (even hardened stuff).
Link found via Google
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scootz
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| posted on 14/8/08 at 12:05 PM |
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Eeek... think I'll be doing this with a pair of welding gloves and a wet suit on!
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alistairolsen
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| posted on 14/8/08 at 12:16 PM |
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unless youre laying up CSM bound with emulsion, or youre only interested in cost, use epoxy
as said tho, with BOTH of them wear gloves and a boilersuit, dont get it in your eyes, avoid breathing fumes as much as possible and have a hot shower
afterwards. (especially if you are/have been grinding)
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BenB
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| posted on 14/8/08 at 12:19 PM |
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Epoxy is bad for your skin (free radicals and all that) but it isn't based upon volatile solvents.
Polyester meanwhile gives off tons of fumes and (unless you've got good ventilation) will quickly gas you (or at the very least give you a
stonking headache and severely drop your sperm count for a few weeks!!)...
Polyester isn't very strong structurally compared to epoxy (e.g. if you get two laminates of same thickness but one is epoxy and one polyester
it's possible to tell which is which)...
Epoxy is expensive. Polyester is cheap.
From a bonding point of view it also depends what you're bonding to what... some things are more compatible with one than the other...
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BenB
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| posted on 14/8/08 at 12:34 PM |
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quote:
Originally posted by alistairolsen
unless youre laying up CSM bound with emulsion, or youre only interested in cost, use epoxy
as said tho, with BOTH of them wear gloves and a boilersuit, dont get it in your eyes, avoid breathing fumes as much as possible and have a hot shower
afterwards. (especially if you are/have been grinding)
If you're grinding then I'd recommend wearing (as ever when grinding) a facemask. Epoxy does kick off free radicals and it makes a very
fine dust. Breathing that in could be bad....
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motorcycle_mayhem
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| posted on 14/8/08 at 02:36 PM |
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Depends what you're bonding....
It's NOT a good idea to use polyester as a bonding agent. Why? Well, when it cures there's a few% shrinkage in volume. This will
pre-stress the bond. To some extent, it's this loss in volume that makes getting your finished article out of a plug less trouble than it would
otherwise be.
Bonding to wood, or general bonding to substrates with polyester can be helped with a polyurethane primer, try 'G4'
Back to epoxy, great as a bonding agent, final characteristics (brittleness, etc.) depend on amount of cross-lnking. Yep, the amines will sensitise
your skin, but let's be a little rational on the exposure you're actually going to get? Styrene (polyester) isn't exactly the best
thing to breath or contact for heavy periods either...
Epoxy isn't too good with UV exposure, doesn't do too well when wet all the time.
If you're bonding (panels, what?) how about a PU product (Sikaflex) or somesuch.
Anyway, ignore all this, I'm a Chemist. Go play.
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scootz
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| posted on 14/8/08 at 03:51 PM |
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It's a fixed wing (spoiler). It's GRP and is quite large / heavy. It will have quite a lot of pressure on it.
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RK
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| posted on 14/8/08 at 04:12 PM |
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From my limited experiences with both, use EPOXY for the reasons above. No headaches. That was enough for me.
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alistairolsen
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| posted on 14/8/08 at 04:14 PM |
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quote:
Originally posted by motorcycle_mayhem
Epoxy doesn't do too well when wet all the time.
If you're bonding (panels, what?) how about a PU product (Sikaflex) or somesuch.
Anyway, ignore all this, I'm a Chemist. Go play.
not arguing, just curious, we use epoxy paints to protect conventional polyester grp from osmosis (water ingress beneath the gelcoat) and the resin in
many cases as a finished surface for yacht hulls....
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twybrow
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| posted on 14/8/08 at 04:15 PM |
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I would look at something like Sikalfex. They have some very good products for structural bonding of GRP. Where I used to work, it was used to stick
the two halves of a boat together, so it really is strong stuff.
Alternatively, depending upon the exact application, you could bond the pieces togther (PU or similar), then layup more CSM over the bond. Again, this
works wonders. We used to pick up an entire hull, on nothing more than carborad tubes with a few layers of CSM/polyester over the top.
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twybrow
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| posted on 14/8/08 at 04:21 PM |
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quote:
Originally posted by alistairolsen
not arguing, just curious, we use epoxy paints to protect conventional polyester grp from osmosis (water ingress beneath the gelcoat) and the resin in
many cases as a finished surface for yacht hulls....
Why not just use isophthalic resins/gelcoats instead?
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Delinquent
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| posted on 14/8/08 at 08:26 PM |
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quote:
Originally posted by twybrow
quote:
Originally posted by alistairolsen
not arguing, just curious, we use epoxy paints to protect conventional polyester grp from osmosis (water ingress beneath the gelcoat) and the resin in
many cases as a finished surface for yacht hulls....
Why not just use isophthalic resins/gelcoats instead?
too hard to spell :p
I used epoxy on the hull of my RC boat as I needed UV stable and totally transparent (polished strip mahogany built) and its stood up to the job
brilliantly. That was on the advice of other RC modellers so am a bit surprised by the not liking wet comment as well. For the UV aspect I did have to
get a specifically high UV one though.
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