Can I substitute vinylester for epoxy?

[Stephen Ditmore]

This vinylester: http://www.aircraftspruce.com/catalo...vinylester.php
sure is more attractively priced than a gallon of epoxy.

• What are the pros & cons of substituting?
• Can I use vinylester to glue things together as I do epoxy resin?
• Can I mix in fillers the same way?
• What's a "promoted" vinylester?

[Eric Sponberg]

Stephen,

Vinylester can be either an epoxy-based resin (better) or an ester-based resin. Both are cured with a peroxide such as Methyl Ethyl Ketone Peroxide (MEKP) in similar proportions as with polyester resin. When it cures, it stays "green" for a longer time than polyester than polyester or epoxy. That is, it takes a lot longer, sometimes days longer, for vinylester to fully cure.

VE has better adhesion than polyester (PE), but is not as good as epoxy.

VE and PE both use styrene as a monomer (liquifier), and in PE not all of the styrene is used in the chemical reaction with the catalyst. Excess styrene flashes off and leaves microscopic holes in the laminate. That's what gives PE its characteristic smell, which is actually the styrene. It is also why PE laminates allow water through. VE does not use all of the styrene either, but it uses a lot more, and any leftover styrene cross-links with itself, incorporating polystyrene within the cured resin. Plastic model kits, such as for cars and boats and planes, are made out of polystyrene. As a result, there are very much fewer holes in the VE laminate, so it is more solid and less porous, and that is why it is used as a barrier coat on the outside laminates of some boat hulls. That is why it is also used for chemical storage tanks such as underground gasoline tanks.

Most fillers you can use, but not coloidal silica (Cab-O-Sil) as a thixotropic agent. Cab-O-Sil simply does not work. There are other thixotropic agents that are used, but I don't know any specific brand names. Others may know.

A "promoted" resin means that it has an "accelerator" mixed in with it that assists in starting and driving over the curing reaction with the catalyst. One of the most common types of accelerator is cobalt naphthenate (CoN), which is a highly reactive and dark bluish purple liquid. You can buy resin (PE or VE) as either "neat" or "promoted". When handling CoN and MEKP, be extremely careful about keeping these two chemical separated because when mixed directly together, they are explosively reactive! A common source of boat plant fires is to pour a little CoN onto a pail or drum of resin, and then pour the MEKP on top of it! BOOM! Good-bye boat plant!

If I were building a one-off plywood boat and I was not allergic to epoxy (which I am not), I would use epoxy. If for some reason I could not use epoxy, such as for allergies, then I would try VE.

I hope that helps.

Eric

[Jimbo1490]

I would add that while both VE and PE resins need a promoter like CoN in order to cure, this promoter results in an unacceptably short shelf life for VE resin. This is why VE is often sold in the 'neat' unpromoted state whereas PE is more customarily sold already promoted for either MEKPO or benzoyl peroxide and sometimes promoted for both /either.

Jimbo

[Stephen Ditmore]

Fantastic, guys.... thanks for the great answer!
Stephen

[YankeeBoater]

Here is an excerpt from a table on resins in Eric Sorenson's book on Powerboats... the entries are tensile strength(PSIx1000), ultimate elongation(%) and 1990 bulk cost($/lb)


Orthophthalic: 7.0, 0.91%, $0.66
Isophthalic: 10.3, 2.0%, $0.85
Vinyl Ester: 11-12, 5-6%, $1.44
Epoxy: 8, 7.7%, $4.39

Most production glass boats are made entirely of ortho-polyester resin, save for the outermost layer, which nowadays will be vinylester or iso-polyester to act as a moisture barrier. As you can see from the table, there is a progression in resin tensile strength and interestingly, elongation - greater stretch ability before failure will allow the laminate to be more forgiving in impacts - so you can be both stronger and 'stretchier'.

What's not shown in the table is that there is a parallel progression in resistance to osmosis of water and chemicals, and also in the strength of bonds between successive layers of the laminate (and also between parts that are tabbed together). So, the better resins are really better in virtually every way, except construction cost.

Water osmosis, which can lead to blistering of the hull, is a function of temperature - so if your boat will be in the water in Florida, the need for 'tight' resins for the purpose of retarding osmosis is actually much higher than it is if you will be boating in Nova Scotia.

[Raggi_Thor]

One problem with polyester boats is that they delaminate when the water inside freezes. In Norway you have to keep the boat in the water all winter OR let it dry a few weeks on land before the winter.

[Jimbo1490]

WRT the epoxy cured state specs quoted above, please keep in mind that there is but one way to cure PE and VE resins; they are either cured or they are not. It's a black or white, on or off, zero or one kind of thing.

But epoxy is another animal altogether. There are literally hundreds of different chemicals that are used to cure epoxy resin. The thing is, they all cure it a bit differently, that is the cured state properties will be different, sometimes WAY different, depending on which curative you use. You can cure a standard EEW 190 resin with, say a polyamide curative and you might get a cured mass that is not outstandingly hard with only modest tensile strength of 5-8,000 psi, but is very tough with high elongation before breaking, but softens easily with moderate heating.

You can then take some of that same exact resin and use a different curative and get an exceptionally hard cured mass with tensile strength over 15,000 psi, poor fracture toughness, somewhat brittle with very little elongation at break and outstanding high temperature service performance. Same resin, different curatives.

So it is perfectly OK to generalize about PE and VE resins, because they are much more consistent and homogenous WRT cured state properties. But without knowing which resin and curative we are talking about, such generalizations are not of much value with epoxies.

Jimbo

[Oldshoe]

hey Guys:

well we tried to replace SP Systems Epoxy from VE Reichold but we end up getting pre release on the component. any suggestions???