How to calculate Epoxy Equivalent Weight & Stoichiometry ?

Calculating Equivalent Weight of Epoxy Mixtures Most formulated products include mixtures of epoxy resins, diluents (reactive and unreactive), fillers, additives,…. 

It is essential to determine the Epoxy Equivalent Weight (E.E.W.) of the mixture to determine proper stoichiometric ratios with the curing agent. This is accomplished with the following equation: 

 Equation 1: E.E.W. of Mixture = Total Weight of Mixture/(Wt. 1/E.E.W. 1 + Wt. 2/  E.E.W.2)

Example 1: A mixture of 80% Liquid Epoxy Resin 1 (E.E.W. = 189), 10% Epoxy Resin 2  ( E.E.W.= 183) and 10% filler 

E.E.W. is determined below: E.E.W. of mixture = 100 /(80/189 + 10/183)

                                              E.E.W. of mixture = 209 

Calculating proper Stoichiometric Ratio for Epoxy Resins and ECI Polyamines The phr (parts by weight per 100 parts of epoxy resin mixture) of the ECI Polyamine can be determined with the following equation: 

 Equation 2: phr = (A.E.W. x 100)/  Resin E.E.W.

 Example 2: Determine the stoichiometric mix ratio in phr of the epoxy resin mixture (E.E.W. 209) in Example 1 with APR Polyamine (A.E.W.=43): 

                    phr = (43 x 100)/ 209 

                    phr = 20.6