The performance of my solvent-borne epoxy curative seems to deteriorate quickly over time. What is the problem?
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||David Dubowik |
Principal Applications Chemist
If you are formulating with amine-based curatives, then solvent selection could be the issue. Epoxy curing agents undergo side reactions with a variety of solvents and plasticizers that can tie up the curing agent's active hydrogens so they cannot react with epoxy groups.
These reactions occur slowly enough that a freshly made paint has good reactivity and performs acceptably. Versus standard polyamides, high solids curing agents, like Ancamide® 2353 and Ancamine® 2143, are more likely to be influenced by solvent selection.
Ester solvents, such as PM acetate, and phthalate ester plasticizers, such as dibutyl phthalate, react with amines forming amides and releasing alcohol. Ketones, like MIBK, react with amines forming ketimines and releasing water. Water contamination in polyamide curing agents will hydrolyze imidazoline rings increasing the viscosity, decreasing the pot life, and reducing wetting.
Package ester and ketone solvents with the epoxy resin to improve your storage stability. Store all raw materials in tightly sealed containers to avoid water contamination.