YesIt'sConcrete:
Who's epoxy do you use? You seem to be suggesting that epoxy peeling on garage floors is mostly a matter of stores selling, and DIY'ers using, less expensive (and by implication) lesser quality epoxy. Besides cost, what is the difference between the epoxy paints you use in your business and the epoxy paints Home Depot sells? And, are you saying that your epoxy garage floor paints would NOT peel under the same conditions that a Home Depot garage floor epoxy paint would peel? My understanding is that epoxy paints are a "mature technology", meaning that there's been no major changes in that technology for some time. Usually, that means that everyone making that product is producing much the same thing as everyone else.
PS: You don't need to know the rest. It explains what 'YesIt'sConcrete" meant when he said "aliphatic urethane". He really meant a moisture cure polyurea that uses an aliphatic di- or tri-isocyanate.
An "alcohol" is anything that has a hydroxyl group (-OH) bonded to a carbon atom. That is, C-OH
A diol or triol is anything with two or three, of them, and a polyol is anything with even more of those things in it.
An "isocyanate" is anything with an -N=C=O group in it.
A di-isocyanate or tri-isocyanate is anything with two or three of 'em
and a polyisocyanate is anything with even more.
You make a polyurethane by allowing a di- and tri-isocyanates to react with polyols. And when that happens:
R1-N=C=O combines with HO-R2 to form R1-(NH)-(C=O)-O-R2
where R1 and R2 are anything with isocyanate and hydroxyl groups in them and that ugly thing that forms between them is a urethane linkage. There's a much better drawing of a urethane linkage here:
http://en.wikipedia.org/wiki/Polyurethane
"Moisture cure polyurethanes" are a special class of "polyurethanes" where instead of having two separate reactants, one with isocyanate groups in it and another with hydroxyl groups in it, you only have that first reactant with the isocyanate groups in it, and it reacts with the H-O-H (water) in the air! Get it? The isocyanates see a water molecule as being two connected hydroxyl groups and reacts with it to form something similar to polyurethane, called a "polyurea". All moisture cure "polyurethanes" are actually "polyureas", not polyurethanes.
In the case of a moisture cure "polyurethane", the reaction goes like this:
R1-N=C=O reacts with H-O-H to form R1-NH2 and CO2 (which gasses off)
(aside: Ammonia gas is NH3. If you replace one of the hydrogens in ammonia with something else, the compound you get is called an "amine".)
the amine that's formed (R1-NH2) then reacts with another isocyanate to form a urea group, like this:
R1-NH2 and O=C=N-R1 forms R1-(NH)-(C=O)-(NH)-R1
And that (almost as ugly) thing in the middle is a "urea" group.
Now, if each R1 has two or three isocyanate groups in it, you can see how exposing a blob of R1 to high humidity would result in a solid polyurea being formed. H2O from the air would react to form urea groups between each R1 molecule and all it's neighbors. That would cause a soft blob (or puddle) of R1 molecules to form a hard hunk, or hard film, of polyurethane plastic.
http://en.wikipedia.org/wiki/Urea
http://en.wikipedia.org/wiki/Polyurea
Now,...
When they say "aliphatic" isocyanate, that word "aliphatic" refers to the nature of the thing at the center of R1, or the thing all the isocyanate groups are connected to. It will typically be a hydrocarbon, which means something made out of carbon and hydrogen atoms that is typically a byproduct of refining crude oil.
Hydrocarbons like propane and benzene are broken down into two general catagories, aliphatic hydrocarbons and aromatic hydrocarbons. Aliphatic hydrocarbons are ones where the carbon atoms are lined up in a row, like propane and butane. Aromatic hydrocarbons are ones where the carbon atoms form rings, like toluene, xylene, benzene and naphthalene and Buckyballs. Generally, aliphatic hydrocarbons have very little smell associated with them, wheras aromatic hydrocarbons have a fairly strong smell. Naphthalene is what moth balls are made of, and they stink.
One of the disadvantages of using aromatic hydrocarbons with isocyanate groups on them as the R1 in our example above is that moisture cure polyureas made using aromatic hydrocarbons tend to yellow with age. If you use an aliphatic hydrocarbon with isocyanate groups on it, and allow it to react with H2O, the polyurea you get won't yellow with age.
For those that are interested in this stuff, this web site covers the subject well:
http://www.pcimag.com/CDA/Articles/Feature_Article/BNP_GUID_9-5-2006_A_10000000000000431366
Also, it should be emphasized that the kind of "polyurethane" we're talking about here has very little in common with the oil based "polyurethane" we use as "varnish" or hardwood floor finish. Read on...
When you make the alkyd resins for "oil based" paints, you cook together various chemicals (including glycerine) together. If you want to make an alkyd based "polyurethane" resin for polyurethane "varnish" or polyurethane hardwood floor finish, you add some di- or tri-isocyanates to the recipe. Glycerine molecules have three -OH groups in them and so the isocyanates you add react with the those hydroxyl groups to form urethane linkages right inside the alkyd resin, making it a "urethane modified alkyd" or "polyurethane" resin. Those urethane linkages are very strong, and they act inside the alkyd resin very much like a roll cage inside of a race car, making that resin much harder if you tried to crush it, and much stronger if you tried to stretch it.
So, for "oil based" polyurethanes, all the urethane linkages are allready formed inside the resins when the can leaves the factory. No urethane linkages form when the product is applied to a substrate.
With the kind of polyurethanes YesItsConcrete is talking about, the urethane or urea linkages form once the product is used, not before. And, because there end up being very many more urethane linkages formed in the isocyanate based polyurethane film than in the "oil based" polyurethane film, these isocyanate kind of of polyurethanes form very much harder and more durable films than the "oil based" polyurethanes do. The only thing the different kinds of polyurethanes have in common are that they all contain urethane or urea linkages, but beyond that, they're completely different and their properties are all different too. So, some polyurethane coatings are very much harder and durable than other polyurethane coatings.
But, if someone just calls something "polyurethane", it's safest to presume they mean the "oil based" stuff cuz most people don't even know about the isocyanate based stuff.