Epoxy resin identification method

There are no simple, proprietary test methods for the crosslinked units in epoxy or cured epoxy resins that have already been converted. The Gibbs Indophenol test of epoxy resin for phenol is a positive reaction (due to the presence of bisphenol A). In contrast to phenolic resins, the chromic acid test of formaldehyde is a negative reaction.
When pyrolyzed below 260°C, all epoxy resins will produce acetaldehyde. The steps are: placing test pods in a pyrolysis tube, covering the filter paper with a freshly prepared 5% nitrocyanide and morpholine in water, and heating in an oil bath to 240°C. When the gas emitted by thermal cracking passes through the filter paper. Blue filter paper indicates epoxy resin.
Epoxy resins can also be identified by the method of dispensing: About 100 milligrams of resin are taken in about 10 milliliters of concentrated sulfuric acid at room temperature, followed by the addition of about 1 milliliter of concentrated nitric acid. Five minutes later, 5% aqueous sodium hydroxide solution was carefully added to the top of the solution. If bisphenol A epoxy resin was present, the cherry red color appeared at the interface between the two layers.