Epoxy resin hardeners (or curing agents) are reactive compounds that can react with epoxies at room temperature or higher temperatures. There are two main categories in curing agents; polyamides and aliphatic polyamines. In the curing period, firstly primary hydrogens on the amines react with epoxy groups to make secondary amines. Then, secondary
amines react with epoxy to cure. Finally, the tertiary amines produced react with epoxy groups to get polymer networks. In order to produce cross-linked polymer networks three active hydrogens and two amine groups must be in the amine hardener chemical structures.

There are many different types of amine hardeners. But in general aliphatic, aromatic and cycloaliphatic amines are used with epoxies. Aromatic hardeners react slowly with epoxies at room temperature due to the steric hindrance by aromatic rings. Therefore, the heat is necessary to initiate the curing period. The curing is achieved in higher temperatures. Aromatic structure provides more chemical and heat resistance compared to aliphatic amines.

Aliphatic amines are very useful for curing at room temperature. The hydrogens in aliphatic amines are very active so they release heat while reacting with epoxies. For this reason, the pot life is very short. The bonds between the aliphatic amines and epoxies are very strong that offers more resistance to alkali and inorganic acids but the solvent resistance
is not good. Aliphatic amines are hazardous and irritates skin.

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