RE: Thinning Epoxy Resin

RE: Thinning Epoxy Resin
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RE: Thinning Epoxy Resin - 9/8/2005 3:32:24 PM

davidfee

Posts: 691
Joined: 6/21/2003
From: San Diego, CA, USA
Status: offline

Lee,
Your C114 fuse looks great! I think Ed cleared up what I was trying to say, which was just that using a slower hardener will offset the increase in curing rate you see when you heat the epoxy. The result is that you have a lower viscosity for better wet-out, and you still have plenty of time to do the work.

FWIW, I did have one "negative" experience when thinning with alcohol to apply light FG over a balsa-skinned wing. Not knowing any better, I picked up "denatured alcohol" from the drug store. I didn't read the label because I figured the stuff would be what I wanted. It turns out that the denaturing agent, rather than being some other alcohol ethyl/methyl, was some form of petrolium distillate. This resulted in a rubbery finished product. I actually experimented with this, once I realized what had happened. I tried using the "denatured alcohol" as a plasticizer to make some flexible FG props. That actually worked fairly well, but the strength seemed to be reduced considerably as compared to props made with un-thinned epoxy.

-David

(in reply to Ed Smith)

Post #: 26

RE: Thinning Epoxy Resin - 9/8/2005 4:54:14 PM

Ed Smith

Posts: 2820
Joined: 12/29/2001
From: Brantford, ON, CANADA
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This is a Direct quote from the West Systems user manual.

Thinning Epoxy

There are epoxy-based products specifically designed to penetrate and reinforce rotted wood. These products, basically an epoxy thinned with solvents, do a good job of penetrating the wood. But the solvents compromise the strength and moisture barrier properties of the epoxy. WEST SYSTEMS epoxy can be thinned with solvents for greater penetration, but not without the same compromise in strength and moisture resistance. Acetone, toluene or MEK have been used to to thin WEST SYSTEM epoxy and duplicate these penetrating epoxies with about the same effectiveness. If you choose to thin epoxy, keep in mind that the strength and moisture protection of the epoxy are lost in proportion to the amount of solvent added.

There is a better solution to get good wood penetration without losing strength or moisture resistance. We recommend moderate heating of the repair area and the epoxy with a heat gun or heat lamp. The epoxy will have a lower viscosity and penetrate more deeply when it is warmed and contacts the warmed wood cavities and pores. Although the working life of the epoxy will be considerably shortened, slower hardeners (206, 207, 209) will have a longer working life and should penetrate more than 205 hardener before they begin to gel. When the epoxy cures it will retain all of its strength and effectiveness as a moisture barrier, which we feel more than offsets any advantages gained by adding solvents to the epoxy.

Ed S

(in reply to davidfee)

Post #: 27

RE: Thinning Epoxy Resin - 9/8/2005 7:54:15 PM

Newflee

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From: Calgary, AB, CANADA
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Thanks for the advice guys. Just a note, the alcohol I use is isopropyl rubbing alcohol 99%. It is my understanding that alcohol can not be held at anything higher than 96% due to its attraction to moisture. This I know from my other distilling hobby. Therefore your warnings about moisture contamination are quite valid. I'm sure that moisture is drawn into the mixture and then even if the alcohol is evaporated off the moisture remains.

I have heard quite a lot of good things about the MGS resins but their website doesn't offer much info on sources. Does anyone know if it is available in Canada?

Lee

(in reply to Ed Smith)

Post #: 28

RE: Thinning Epoxy Resin - 9/8/2005 9:42:28 PM

Ed Smith

Posts: 2820
Joined: 12/29/2001
From: Brantford, ON, CANADA
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The distributor in Canada is:-

Airheart Distributing,
55 Lancing Drive,
Unit 1.
Hamilton,
ON. L8W 2Z9

They should be able to help with sources.

Ed S

(in reply to Newflee)

Post #: 29

RE: Thinning Epoxy Resin - 9/9/2005 12:24:49 AM

Newflee

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From: Calgary, AB, CANADA
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Great thanks Ed.

Lee

(in reply to Ed Smith)

Post #: 30

RE: Thinning Epoxy Resin - 9/21/2005 5:45:39 AM

sticks-RCU

Posts: 126
Joined: 4/18/2002
From: ogden, UT, USA
Status: offline

MGS rules, I have been using it for a couple of years now and love it. If I am working on a large project I will use their slow hardner that gives you a few hour pot life and it wets out great. If I am working on something smaller, I will use their faster hardner. I just hate it when I am trying to lay something up and the epoxy gets all sticky.

(in reply to Newflee)

Post #: 31

RE: Thinning Epoxy Resin - 10/12/2005 8:46:58 PM

gluedoc

Posts: 22
Joined: 1/16/2004
From: Great Mills, MD, USA
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quote:

ORIGINAL: Newf

Thanks for the advice guys. Just a note, the alcohol I use is isopropyl rubbing alcohol 99%. It is my understanding that alcohol can not be held at anything higher than 96% due to its attraction to moisture. This I know from my other distilling hobby. Therefore your warnings about moisture contamination are quite valid. I'm sure that moisture is drawn into the mixture and then even if the alcohol is evaporated off the moisture remains.

I have heard quite a lot of good things about the MGS resins but their website doesn't offer much info on sources. Does anyone know if it is available in Canada?

Lee

A minor correction Lee. Isopropyl alcohol at 99% will stay pretty close to 99% if you keep it in a sealed container. The 96% content that you are talking about is the vapor-liquid equilibrium azeotrope for ethyl alcohol, which prevents you from distilling the ethanol to more than 96% purity. However, this azeotrope can be broke with the addition of a cosolvent (benzene or octane work well), and the ethanol can then be distilled to near 100% purity. This product is perfectly stable with respect to moisture absorbtion, and is what is known as denatured alcohol. In addition, the azeotrope can be broked using liquid-solid extractions, but that is too far afield to discuss here.

Matt

(in reply to Newflee)

Post #: 32

RE: Thinning Epoxy Resin - 10/12/2005 8:57:05 PM

gluedoc

Posts: 22
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From: Great Mills, MD, USA
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Let me provide some minor contributions here.

First, thinning epoxy resins is certainly permissible, and a very necessary thing. Usually, this is done for the purposes of spraying the epoxy (e.g. paint) where most of the solvent will volatilize during the aerosol process. However, there has been some work performed in the commercial and military aerospace industry regarding the use of structural spray epoxies. Largely, the key to their success is the COMPLETE removal of volatiles prior to cure. In this case, these are heat cured materials, so degassing is possible. In the case of room temperature cure epoxies, this is never completely possible. Those of you who are thinning your epoxies are introducing voids in your laminates at around 5-20%. This can significantly weaken the laminates, but composites used in models are so overdesigned that it doesn't matter much.

The solution to this problem is to use a less viscous epoxy to begin with. The five and thirty minute varieties use a fairly viscous epoxy as their primary ingredient in both the part A and B. When a less viscous material is used (for RTM or VaRTM applications), a thinner epoxy is blended in to the mixture (such as an aliphatic epoxy). In addition, the use of elevated temperature cure catalysts allow the resin to flow significantly as it is heated, providing a more uniform surface.

The bottom line on this issue is that pinholes in the surface don't affect structural integrity, but require rework and lead to added weight to get a smooth surface. Voids on the interior of a laminate can lead to delaminations and component failure. A good way to prevent both is to edge bleed a wet laminate, and make sure that you don't suffer from bridging or resin pooling because your vacuum distribution medium isn't adequate.

Matt

(in reply to gluedoc)

Post #: 33

RE: Thinning Epoxy Resin - 10/13/2005 12:10:49 AM

chelapa

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Joined: 1/28/2005
From: , NY, USA
Status: offline

well. ok guys. i love your write ups. esp the last one on this thread. Now, i hear mgs is good. How good. what is the mix ratio in weight. and, i need something that i only have to pay about 40-50 per gal. if less then that would be even better. I cant spend to much money here. got any links??!?!?!

(in reply to gluedoc)

Post #: 34

RE: Thinning Epoxy Resin - 10/13/2005 2:31:40 AM

davidfee

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Joined: 6/21/2003
From: San Diego, CA, USA
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quote:

ORIGINAL: chelapa

well. ok guys. i love your write ups. esp the last one on this thread. Now, i hear mgs is good. How good. what is the mix ratio in weight. and, i need something that i only have to pay about 40-50 per gal. if less then that would be even better. I cant spend to much money here. got any links??!?!?!

MGS H285/L285/L287 is marketed for use in the aviation industry (has been a standard product for 20 years). For that reason, it must meet strict quality standards and have fully explored chemical and physical data. Full scale aircraft must be certified, so they must be made with quality stuff. If you read the data sheets for MGS, you find that the manufacturer specifies a post-cure at elevated temperature to complete the cure and stabilize the part. For most hobby applications, the post-cure is not actually needed.

The MGS resin and hardener are low-viscosity (600-900 cps for resin, 50-100 cps for hardener), so they wet out fabrics quickly. The mix ratio is 100:40 by weight and 100:50 by volume.

In the US, MGS is about $80/gallon for the resin only... and another $40 or so for the hardener. Is it worth it? Perhaps not for every application. However, I love the stuff.

-David

(in reply to chelapa)

Post #: 35

RE: Thinning Epoxy Resin - 10/13/2005 7:23:27 AM

davidfee

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From: San Diego, CA, USA
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quote:

ORIGINAL: gluedoc
...and the ethanol can then be distilled to near 100% purity. This product is perfectly stable with respect to moisture absorbtion, and is what is known as denatured alcohol.

Thanks for your contributions. Care to elaborate on this a bit? How is ~100% ethanol moisture-stable (i.e. not hygroscopic)? Also, denaturing typically refers to the "adulteration" of ethanol with some small percentage of methanol, does it not?

thanks,
-David

(in reply to gluedoc)

Post #: 36

RE: Thinning Epoxy Resin - 10/13/2005 5:41:16 PM

gluedoc

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From: Great Mills, MD, USA
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quote:

ORIGINAL: davidfee

quote:

ORIGINAL: gluedoc
...and the ethanol can then be distilled to near 100% purity. This product is perfectly stable with respect to moisture absorbtion, and is what is known as denatured alcohol.

Thanks for your contributions. Care to elaborate on this a bit? How is ~100% ethanol moisture-stable (i.e. not hygroscopic)? Also, denaturing typically refers to the "adulteration" of ethanol with some small percentage of methanol, does it not?

thanks,
-David

We are way off topic here, and you all have a very adoit understanding of this, just seem to be missing a few of the details. If you leave nearly any substance exposed to humid air, it will pick up water. This has to do with vapor/liquid or vapor/solid equilibria. If you want anything to stay absolutely moisture free, then you have to store it in packed in an inert gas. Yes, denatured alcohol, or even non-denatured pure ethanol will pick up environmental moisture. However, if the purity of the alcohol is above the azeotrope, it will never pick up more than 4% water (from the atmosphere), the nature of the azeotrope works both ways. Technically, this does not make the material hygroscopic (as that refers to an acceleration of condensation or a scavenging of water vapor), but your point is the same.

As for the term denatured, you are correct. It does refer to the addition of a second substance to the ethanol. This substance can be added for the express purpose of making the alcohol non-potable (and thus, tax free for industrial purposes), but it can also be added to break the azeotrope and obtain pure ethanol. The second process is needed to make pure ethanol for blending with gasoline, and iso-octane is often used in that case to break the azeotrope.

Matt

(in reply to davidfee)

Post #: 37

RE: Thinning Epoxy Resin - 10/14/2005 2:14:25 AM

davidfee

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From: San Diego, CA, USA
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Thanks, Matt.

I do have an M.S. in physical chemistry, so this is not mysterious to me. I just simply wanted a bit of clarification because I wasn't sure if we were on the same page about these things.

-David

(in reply to gluedoc)

Post #: 38

RE: Thinning Epoxy Resin - 10/16/2005 9:45:59 PM

branded

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Joined: 7/16/2002
From: cary, IL, USA
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quote:

ORIGINAL: Ed Smith

quote:

If you need to reduce the working viscosity of your epoxy... just warm it up and use a slower hardener if needed.

I totally agree with David. I tell people time and time again that thinning epoxy is detrimental to the end product. Wests Systems own literature recommends that in order to maintain all of the resin's properties the epoxy should not be thinned.

The choice of resin is important here. West systems epoxy is a top quality product. However West's slowest hardener does not give a very long working time, about 45 minutes. I use MGS epoxy resin. The fast hardener allows a 20 min. working time while the slow will allow about 4 hours. The two hardeners can be mixed for the working time of one's choice between those two limits. When glassing a wing I do as David suggested. I use a slow hardener and warm the resin with a heat gun as I apply it. The resin will go on really thin with this method. You will save resin (Money) and weight.

Ed S

I think you need to seperate your argument of thinning epoxy by it's application. It's perfectly acceptable to thin epoxy, whether it be West System or other, with Alcohol for purposes of covering a model with glass. If the application is structural, such as in laminating, or reinforcing firewalls, etc. then it's not advisable to thin.

Epoxy has long been used as a filler for glass on models. When used in this way the epoxy is thinned just to the consistancy of milk using alcohol. It is used to apply the gla