Epoxy equivalent weight

The epoxide equivalent weight (abbreviation EEW , English Epoxy Equivalent Weight ) is a measure of compounds which epoxy containing groups. The epoxy equivalent weight describes the mass in grams which one mole of epoxy groups contains. It is used, for example, as a key figure for epoxy resins , for use as adhesives , casting resins or paints .

Determination of the epoxy equivalent weight

Procedure A

For the determination according to method A, chloroform and glacial acetic acid are added to a sample of the resin , and the sample is dissolved while warming gently. Then 10 ml of tetraethylammonium bromide solution and a few drops of indicator are added. The mixture is then titrated to blue-green with perchloric acid . A blank test is carried out in the same way, but without epoxy resin.

With the parameters determined, the epoxy equivalent weight EEW is calculated according to the following equation . The temperature must be taken into account due to the expansion coefficient of perchloric acid.

${\displaystyle EEW={\frac {M_{E}*1000}{(a-b)*[1-{\frac {t_{1}-t_{2}}{1000}}]*n}},[{\frac {g}{mol}}]}$

• ME weight in grams

• a Consumption of perchloric acid c (HClO ₄ ) = 0.1 mol / l in ml of the main experiment
• b Consumption of perchloric acid c (HClO ₄ ) = 0.1 mol / l in ml of the blank sample
• t ₁ temperature of the perchloric acid during the titration
• t ₂ temperature of the perchloric acid during adjustment
• n titer of perchloric acid c (HClO ₄ ) = 0.1 mol / l

The reaction of tetraethylammonium bromide with perchloric acid produces hydrogen bromide , which reacts with the epoxide groups present. As soon as no more hydrogen bromide is consumed, the indicator shows the falling pH value.

Procedure B

For the determination according to method B, an excess of hydrochloric acid is added to a sample of the resin . The excess that is not used is titrated. The sample is dissolved in methyl ethyl ketone and then mixed with a defined volume of MEK / HCl solution (excess HCl). The sample is left to rest for 30-45 minutes and then 3 ml of deionized water are added. It is titrated with a KOH solution (0.1 mol / l) against the added indicator cresol red . A blank sample is also used. The epoxy equivalent weight EEW is calculated according to the following equation.

${\displaystyle EEW={\frac {M_{E}*10}{(a-b)*F}},[{\frac {g}{mol}}]}$

• ME weight in grams

• a Consumption of potassium hydroxide solution c (KOH) = 0.1 mol / l in ml of the blank sample
• b Consumption of potassium hydroxide solution c (KOH) = 0.1 mol / l in ml of the main experiment
• F factor of the potassium hydroxide solution c (KOH) = 0.1 mol / l

When hydrochloric acid and epoxides react, chlorohydrin is formed , which means that the amount of hydrochloric acid to be titrated is lower in the presence of epoxide groups.

Other common units and information

Epoxy number

The epoxy number EZ indicates how many grams of epoxy groups 100 g of epoxy resin contain. Epoxy groups weigh 43 g / mol. The conversion between epoxy equivalent weight and epoxy number is carried out according to the following equation.

${\displaystyle EEW={\frac {43*100}{EZ}}\Leftrightarrow EZ={\frac {43*100}{EEW}}}$

Epoxy value

The epoxy value EW is the reciprocal of the epoxy number and thus describes the number of epoxy groups that are contained in 100 g of resin. The conversion between epoxy equivalent weight and epoxy value is carried out according to the following equation.

${\displaystyle EW={\frac {100}{EEW}}\Leftrightarrow EEW={\frac {100}{EW}}}$

Epoxy index

In contrast to the epoxy value, the epoxy index EI indicates the number of epoxy groups contained in 1 kg of resin. The conversion between epoxy equivalent weight and epoxy index is carried out according to the following equation.

${\displaystyle EI={\frac {1000}{EEW}}\Leftrightarrow EEW={\frac {1000}{EI}}}$

Epoxy oxygen

The epoxy oxygen ES indicates how many grams of epoxy oxygen (i.e. the mass of oxygen that is present in the resin via epoxy groups) are contained per 100 g of resin. The conversion between epoxy equivalent weight and epoxy oxygen is carried out according to the following equation.

${\displaystyle ES={\frac {100*16}{EEW}}\Leftrightarrow EEW={\frac {100*16}{ES}}}$

Further literature

• DIN EN ISO 7142
• DIN EN ISO 3001
• H. Kittel, Textbook of Paints and Coatings, Volume 2, 2nd Edition, S. Hirzel, Stuttgart 1998, pp. 267-318

Individual evidence

1. ↑ ^{a b} Michael Dornbusch, Ulrich Christ, Rob Rasing: Epoxy resins: Fundamentals and applications . 1st edition. Vincentz Network, Hannover 2015, ISBN 978-3-86630-604-2 .
2. ↑ German Institute for Standardization (ed.): DIN 16945 . Beuth Verlag, Berlin March 1989.