1,886.8
g/eq
0.53
eq/kg
0.85
%
2.28
%
5.3
mL
0.53
meq/g
1,886.8
g/eq
0.53
eq/kg
0.85
%
2.28
%
5.3
mL
0.53
meq/g
The Epoxide Equivalent Weight (EEW) calculator determines the mass of resin in grams containing one equivalent of epoxide groups. This is the defining quality parameter for epoxy resins — the most widely used thermosetting polymers in adhesives, coatings, composites, and electronic encapsulation. The EEW directly controls the stoichiometric ratio of resin to hardener (curing agent) needed for optimal crosslinking. Common liquid DGEBA (diglycidyl ether of bisphenol A) resins have EEW of 170-200 g/eq, while solid grades range from 400-3000+ g/eq. This calculator also provides the epoxide content percentage and oxirane oxygen content, which are alternative ways of expressing the same information required by ASTM D1652 and ISO 3001 standards for quality control of epoxy resins.
The EEW is determined by titrating the epoxide groups with hydrogen bromide (HBr) in acetic acid, or perchloric acid in the presence of tetraethylammonium bromide:
$$\text{Epoxide} + HBr \rightarrow \text{Bromohydrin}$$
The ring-opening reaction is quantitative:
$$\overset{O}{\underset{/\;\backslash}{CH-CH}} + HBr \rightarrow HO-CH-CH-Br$$
The epoxide equivalent weight is:
$$EEW = \frac{W \times 1000}{(V - V_{blank}) \times N}$$
where $$W$$ is the sample weight (g), $$V$$ is the titrant volume (mL), $$V_{blank}$$ is the blank volume, and $$N$$ is the normality.
Related parameters:
$$\%\text{Epoxide} = \frac{43.04}{EEW} \times 100$$
$$\%\text{Oxirane oxygen} = \frac{16.00}{EEW} \times 100$$
where 43.04 is the molecular weight of the epoxide group (C₂H₃O) and 16.00 is the atomic weight of oxygen.
Standard liquid DGEBA epoxy resins have EEW 170-195 g/eq (theoretical pure DGEBA = 170 g/eq). Higher EEW indicates either higher molecular weight (more advanced resin) or lower epoxide content due to side reactions. For curing calculations: parts of hardener per 100 parts resin (phr) = (EEW × AHEW ratio) / 100, where AHEW is the amine hydrogen equivalent weight. Common epoxy types: Liquid DGEBA (EEW 182-192), Solid DGEBA (EEW 400-3000), Novolac epoxy (EEW 170-210), Cycloaliphatic epoxy (EEW 130-145), Epoxidized soybean oil (EEW 220-250). The oxirane oxygen content for liquid DGEBA is typically 8.2-9.4%, while epoxidized vegetable oils range from 6-7%.
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EEW = (1.0 × 1000)/(5.3 × 0.1) = 188.7 g/eq. Typical for standard liquid DGEBA resin (e.g., Epon 828).
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EEW = (2.0 × 1000)/(8.5 × 0.1) = 235.3 g/eq. Higher EEW reflects the larger molecular weight and fewer epoxide groups per molecule.
Epoxide equivalent weight (EEW) is the mass of resin in grams that contains one mole of epoxide groups. It is the primary specification for epoxy resins and determines the stoichiometric ratio of resin to curing agent needed for complete crosslinking. Lower EEW means more epoxide groups per gram (more reactive).
For amine hardeners: phr (parts per hundred resin) = (AHEW / EEW) × 100, where AHEW is the amine hydrogen equivalent weight of the hardener. For example, with EEW = 190 and AHEW = 50: phr = (50/190) × 100 = 26.3 parts hardener per 100 parts resin.
DGEBA (diglycidyl ether of bisphenol A) is the most common epoxy resin, formed by reacting bisphenol A with epichlorohydrin. The ideal structure has MW = 340 and EEW = 170, but commercial products are mixtures with EEW of 182-192 due to oligomer formation.
Solid epoxy resins are higher molecular weight oligomers of DGEBA containing additional bisphenol A units in the chain but the same two terminal epoxide groups. As the chain grows, the molecular weight increases but the epoxide count stays at 2, so EEW = MW/2 increases proportionally.
Oxirane oxygen content is the weight percentage of oxygen in epoxide rings. It equals 16/EEW × 100. For liquid DGEBA (EEW ~188), oxirane oxygen is about 8.5%. This parameter is commonly used in the epoxidized vegetable oil industry and is specified in ASTM D1652.
Yes. EEW is the primary quality specification for epoxy resins. Suppliers guarantee EEW within a specified range (e.g., 182-192 for standard liquid DGEBA). Deviations indicate manufacturing variability, incomplete epoxidation, or degradation during storage.
The ASTM D1652 method uses a solution of HBr in glacial acetic acid as titrant, with crystal violet indicator (purple → green endpoint). An alternative perchloric acid method uses tetraethylammonium bromide in chloroform/acetic acid. Both methods give equivalent results.
Water can react with epoxide groups through hydrolysis, opening the ring and forming a diol. This consumes epoxide groups without being detected by the titration, leading to an artificially high (worse) EEW value. Epoxy resins should be stored sealed to prevent moisture absorption.
Liquid DGEBA resins typically have a shelf life of 2 years at room temperature in sealed containers. The EEW gradually increases over time due to homopolymerization and hydrolysis. Monitoring EEW periodically is recommended for resins in long-term storage.
Cycloaliphatic epoxies have the epoxide group fused to a cyclohexane ring rather than being a terminal glycidyl ether. They have lower EEW (130-145), better UV resistance, and excellent electrical properties. They are preferred for outdoor coatings, LED encapsulation, and high-voltage insulation.
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