HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Jul 27, 2011, 07:44 PM
Micro Boat Forum Founder
boredom.is.me's Avatar
United States, GA, Buford
Joined Nov 2007
6,521 Posts
Question
Can epoxy resin be mixed with polyester resin?

This has no real relation to rc, but still pertains to composites.


Polyester resin does not bond to carbon fiber that well.
Polyester resin bonds to fiberglass very well.
Polyester resin also works with aramid fibers.
Polyester resin is commonly used on full sized boats due to the final costs.
Vinyl ester resin the mid point between polyester resin and epoxy resin, but still shares the adhesion properties of polyester resin.
Epoxy is mainly used to repair full sized boats because of its properties.
Epoxy bonds to fiberglass, carbon fiber, and aramid fibers very well.
Epoxy is about 3.5 times more expensive than polyester resin.
Fiberglass, carbon fiber, and aramid fibers all follow a general rule of a given weight of resin to an equivalent weight of fiber.
An object made of all carbon fiber and epoxy will have a resin cost 3.5 times higher than that of an object made from fiberglass and polyester.

Additional:
Epoxy resin will stick to polyester resin.
Polyester resin will not stick to epoxy resin.
Assumption - Epoxy resin will stick to vinyl ester resin.


All of this leads to this: Can polyester or vinyl ester resin be mixed with epoxy resin?
boredom.is.me is offline Find More Posts by boredom.is.me
RCG Plus Member
Last edited by boredom.is.me; Jul 27, 2011 at 07:57 PM.
Reply With Quote
Sign up now
to remove ads between posts
Old Jul 27, 2011, 07:57 PM
chetosmachine's Avatar
Madrid, Spain
Joined Sep 2004
1,102 Posts
Quote:
Originally Posted by boredom.is.me View Post
Epoxy is about 3.5 times more expensive than polyester resin.
An object made of all carbon fiber and epoxy will have a resin cost 3.5 times higher than that of an object made from fiberglass and polyester.
Sorry but NO.
You're assuming fiberglass and carbon at the same price so you either are being stolen in your fiberglass or I would like to know your source of carbon.
I would say, given your resin costs ratio, a full carbon object costs at least 35 times higher than an object made from fiberglass and polyester.

BUT
the characteristics of both objects being absolutely different, what's the point of that comparison?


BTW, epoxy bond to polyester is poor. Mainly because laminating poliester resin has some wax on it to allow non tacky surfaces. And I have found polyester resin impregnates the carbon cloth as good as the epoxy. So your first sentence has not much sense to me.
chetosmachine is offline Find More Posts by chetosmachine
Reply With Quote
Old Jul 27, 2011, 08:05 PM
Micro Boat Forum Founder
boredom.is.me's Avatar
United States, GA, Buford
Joined Nov 2007
6,521 Posts
You missed the key part of that statement.
An object made of all carbon fiber and epoxy will have a resin cost 3.5 times higher than that of an object made from fiberglass and polyester.
This excludes the cost of the fiber.

--------------------------

I do not mean using one on top the other. I mean combining the resins before they are applied to the fiber.
boredom.is.me is offline Find More Posts by boredom.is.me
RCG Plus Member
Latest blog entry: RFD900 Case
Reply With Quote
Old Jul 27, 2011, 08:24 PM
Composites Kid
Alex.Schweig's Avatar
Lima, Peru
Joined Jul 2008
3,122 Posts
Impossible. Some epoxies will be inhibited from curing by the addition of polyester. A particular example of this is Resin Research epoxy - a friend of mine who is into surfboard manufacture accidentally mixed clear polyester (Silmar 49, catalyzed) with Resin Research epoxy (already mixed). The resulting compound never cured, even when heated repeatedly.

Mixing between different epoxy systems is not a good idea. Mixing two widely differing thermoset chemistries, ie, epoxy and polyester, is a clear no-no.

Additionally, I have heard of bad exotherm issues when polyester and aramid are used together - it seems there is a compatibility issue here.

In my own experience, polyester is a finicky, inconvenient system. The extra cost of epoxy laminating resins is taken up quickly when you consider it´s ease of use, superior chemical and mechanical properties, and lower VOC content.

So... if you want a compromise, either use a low-cost epoxy, or vinylester resin. Epoxy is not that expensive... USC 635 is an excellent system. Check out wyowindworks´ comparison of epoxy systems to see how it fares against more expensive epoxies. It´s only $60 a gallon.

My two cents,
-Alex
Alex.Schweig is offline Find More Posts by Alex.Schweig
Reply With Quote
Old Jul 27, 2011, 08:24 PM
G_T
Registered User
Joined Apr 2009
5,818 Posts
Hmmm, mix random reactive complex chemistry together and see what happens... Sounds like the start of a Darwin Award experiment. Seriously, don't mix chemicals together if you don't know what the outcome will be.

These chemicals are not designed to be mixed together.

Gerald
G_T is offline Find More Posts by G_T
Reply With Quote
Old Jul 27, 2011, 08:34 PM
Registered User
sscherin's Avatar
USA, WA, Kennewick
Joined Nov 2005
502 Posts
The extra cost depends on what epoxy you are buying..

The US composites 635 gallon kit with fast hardener makes 1.5 gal mixed for $69

1.5 gallons of USC 435 poly resin is about $44.. So 635 is about 1.6 times more expensive but much nicer to work with indoors.

USC 700 Vinyl Ester is $64 for 1.5 gallons so right in the same ball park as 635 epoxy

West 105 is $80 for a gallon plus $31 for a quart of 205.. so adjusted to 1.5 gal it's $133
or 3x more expensive than poly..

MGS at $203 for 1.5 gal mixed so yeah now we are in the 4x more expensive ball park.

I guess my point is if I were try and save $$ I'd rather use a less expensive epoxy then try to mix materials.
sscherin is online now Find More Posts by sscherin
Reply With Quote
Old Jul 27, 2011, 09:07 PM
Father of Fr3aK, DLG Pilot
tom43004's Avatar
USA, OH, Worthington
Joined May 2002
6,738 Posts
Honestly if you're looking for laminates that have certain physical properties then you need to design toward the physical properties. Find a cheap resin that has the physical properties you're willing to live with and use it.

If physical properties don't matter and you're worried about cost, then you should be looking at casting with cheaper polymers rather than laminating composites.

Two part resins of any chemical makeup are formulated to a fairly exact molecular ratio. Any "miss" on that ratio and you're getting a percentage of the resin that becomes a "liquid filler" around those molecules that do successfully react. Mixing any of these without knowing exactly what you're doing is dangerous and probably will net you some really rubbery messes, if you're lucky enough for them to even get that far.
tom43004 is offline Find More Posts by tom43004
Reply With Quote
Old Jul 27, 2011, 09:25 PM
Micro Boat Forum Founder
boredom.is.me's Avatar
United States, GA, Buford
Joined Nov 2007
6,521 Posts
I do get the very strong message. I was just curious to know if it was possible.

Thanks guys.

I guess I should have mentioned that it was for a full size boat. We want to make a copy of a one off 17 foot vee hull.
boredom.is.me is offline Find More Posts by boredom.is.me
RCG Plus Member
Latest blog entry: RFD900 Case
Reply With Quote
Old Jul 27, 2011, 10:50 PM
Just fly it!
wyowindworks's Avatar
Cody, WY
Joined Nov 2007
6,915 Posts
"Polyester resin does not bond to carbon fiber that well."
I think it's better to say the epoxy bonds to carbon fiber better than polyester. Polyester does bond to carbon but the inter-laminar bond is better with epoxy. If you are going to use polyester with carbon fiber it's important that the carbon is sized with a sizing that is compatible with polyester.

"Polyester resin bonds to fiberglass very well."
So does epoxy. The finish on the glass actually facilitates a chemical bond between the glass and the resin. It's important to used a glass that has been treated with a finish that is compatible with your resin choice.

"Polyester resin also works with aramid fibers."
So does epoxy. Epoxy typically yields a better inter-laminar bond between kelvar 49. Kevlar 49 usually exhibits the poorest inter-laminar bond of the 3 fibers (glass, carbon, Kevlar). For this reason other fibers (glass, carbon) are often woven with the Kevlar to facilitate a better inter-laminar bond.

"Polyester resin is commonly used on full sized boats due to the final costs."
True enough. Hulls made with polyester typically have a weaker impact strength than those made with epoxy.

"Vinyl ester resin the mid point between polyester resin and epoxy resin, but still shares the adhesion properties of polyester resin."
I'm not sure about that one. I'm pretty sure that vinyl ester has better bonding attributes than polyester. The big down side to vinyl ester resin is a very short shelf life.

"Epoxy is mainly used to repair full sized boats because of its properties."
Very true. Since epoxy has higher bonding attributes it makes sense to use epoxy because a chemical bond cannot be facilitated.

"Epoxy bonds to fiberglass, carbon fiber, and aramid fibers very well."
The epoxy bond is typically better than other laminating polymers. Again, kevlar is NOT used in many applications because inter-laminar failure is common in laminates that undergo lots of stress.

"Epoxy is about 3.5 times more expensive than polyester resin."
Depends on the resin.

"Fiberglass, carbon fiber, and aramid fibers all follow a general rule of a given weight of resin to an equivalent weight of fiber."
I have no idea what you are trying to say. The specific gravity between the 3 fibers is different. If a glass laminate had a 50:50 ratio by weight it would be 30% fiber by volume. A carbon laminate with a 50:50 ratio by weight would be around 37% fiber by volume. A 50:50 Kevlar laminate by weight would be around 43% fiber by volume. The fiber, fabric weave, and fabric weight can really effect the fiber to resin ratio that you can get with an unassisted hand layup.

"An object made of all carbon fiber and epoxy will have a resin cost 3.5 times higher than that of an object made from fiberglass and polyester."
Depends on the resin chosen, the bulk and weave within the fabric, the process used to fabricate the part.

"Additional:
Epoxy resin will stick to polyester resin."
Quite true. It's important to properly prep the bonding surfaces.

"Polyester resin will not stick to epoxy resin."
It will stick but not as well as epoxy will.

"All of this leads to this: Can polyester or vinyl ester resin be mixed with epoxy resin?"
Absolutely not! Polyester and vinyl ester use MEKP to initiate a reaction between the monomers. Using more MEKP will cause the reaction to happen faster. Using less with slow the reaction. Epoxies cure via poly-addition. Meaning that the molecules within the hardener link with molecules within the resin. Adding too much hardener will result in too many molecules of one kind. These molecules won't be able to find a mating connection. They will actually then get in the way and further block the linking. Typically the resin will end up being more flexible due to the lower level of cross-linking and the increased space between the polymer chains. If not enough hardener is used then the resin molecular connections will go unfulfilled. No one wants unfulfilled epoxide groups. They then feel very lonely and live out their lives with unfulfilled potential. If you listen closely you can hear them cry.

Quote:
Originally Posted by chetosmachine View Post
BTW, epoxy bond to polyester is poor. Mainly because laminating poliester resin has some wax on it to allow non tacky surfaces. And I have found polyester resin impregnates the carbon cloth as good as the epoxy. So your first sentence has not much sense to me.
Wax typically isn't added to polyester resins that used for laminating. Wax is often added (referred to as finishing resin) to polyester so it doesn't cure with a tacky surface. The wax floats to the top of the surface and creates a seal to prevent the resin from reacting with the atmosphere. If bonding is desired, this wax must be sanded off and then the surface should be cleaned with strong solvent. If you know that bonding will need to take place you shouldn't use a polyester that has wax added to it. Epoxy, if the surfaces are properly prepped, will bond to a cured polyester better than polyester will.
wyowindworks is offline Find More Posts by wyowindworks
Last edited by wyowindworks; Jul 27, 2011 at 11:24 PM.
Reply With Quote
Old Jul 27, 2011, 11:25 PM
Micro Boat Forum Founder
boredom.is.me's Avatar
United States, GA, Buford
Joined Nov 2007
6,521 Posts
Wow, I really appreciate what you put into your post.

"Fiberglass, carbon fiber, and aramid fibers all follow a general rule of a given weight of resin to an equivalent weight of fiber."
I have no idea what you are trying to say. The specific gravity between the 3 fibers is different. If a glass laminate had a 50:50 ratio by weight it would be 30% fiber by volume. A carbon laminate with a 50:50 ratio by weight would be around 37% fiber by volume. A 50:50 Kevlar laminate by weight would be around 43% fiber by volume. The fiber, fabric weave, and fabric weight can really effect the fiber to resin ratio that you can get with an unassisted hand layup.

I got that bit of info from USComposites.
Quote:
28. How much epoxy do do I need for saturating my fiberglass?

This is a very common and complex question. Each type of fiberglass saturates resin at different ratios. Below is a brief summary of the saturation rates for different reinforcements.

Chopped Strand Mat: Approx. 2 pounds of resin for 1 pound of mat
Fiberglass Woven Cloth: Approx. 1 pound of resin for 1 pound of cloth
Biaxial (1708,1208,1808): Approx. 1-1/2 pounds of resin for 1 pound of biaxial
Carbon Fiber and Kevlar Cloths: Approx. 1 pound of resin for 1 pound of cloth

Your technique for application and experience will determine the exact amount needed but the ratios shown above provide a good starting point. For reference, 1 gallon of epoxy weighs about 9 pounds.
boredom.is.me is offline Find More Posts by boredom.is.me
RCG Plus Member
Latest blog entry: RFD900 Case
Reply With Quote
Old Jul 28, 2011, 12:53 PM
G_T
Registered User
Joined Apr 2009
5,818 Posts
Another reason Kevlar is not likely used much for boats (larger than Kayaks) is that Kevlar is weakened by exposure to moisture. That may be true of aramid fibers in general (Kevlar is two Dupont trademarked aramids), which as I understand it are a subclass of polyester fibers.

Gerald
G_T is offline Find More Posts by G_T
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Epoxy or Polyester resin?? spitfirem9 Slope 6 Mar 02, 2005 01:56 AM