Builders' Forum Archives
Re: Amine Blush
Posted by Steve Miller on Jun 21, 2005
And here is the chemical explanation from System 3. Note that they seem to be saying that improper ratio (measuring errors) can lead to excess amines and therefore blush. Or am I reading it wrong?
Be sure to measure accurately and mix well. I like to mix small batches 2 minutes and batches larger than a few ounces at least 3 minutes. Note that you can mix too long.
From the System 3 "Epoxy Book":
Reactive amine groups are nitrogen atoms with one or two hydrogen atoms attached to the nitrogen. These hydrogen atoms react with oxygen atoms from glycidyl groups on the epoxy to form the cured resin - a highly crosslinked thermoset plastic. Heat will soften, but not melt, a cured epoxy. The three dimensional structure gives the cured resin excellent physical properties. The ratio of the glycidyl oxygens to the amine hydrogens, tak- ing into account the various molecular weights and densities involved, determines the final resin to hardener ratio. The proper ratio produces a “fully-crosslinked” thermoset plastic. Varying the recommended ratio will leave either unreacted oxygen or hydrogen atoms depending upon which side is in excess. The resultant cured resin will have lower strength, as it is not as completely crosslinked. Excess Part B results in an increase in moisture sensitivity in the cured epoxy and should be avoided. Amine hardeners are not “catalysts”. Catalysts promote reactions but do not chemically become a part of the finished product. Amine hardeners mate with the epoxy resin, greatly contributing to the ultimate properties of the cured system.
In Response to: Re: Amine Blush by Steve Miller on Jun 21, 2005