Epoxy value is an important performance index of epoxy resin, which can be used to identify the quality of epoxy resin or calculate the amount of curing agent.
Determination method of epoxy value: hydrochloric acid-acetone method, hydrochloric acid-acetone method is one of the most commonly used methods for determining epoxy value. The specific operation is as follows:
（1） Prepare hydrochloric acid-acetone solution: Take 1 unit volume of hydrochloric acid (AR), add it to 40 unit volumes of acetone (AR), shake well, put it into a reagent bottle with a corresponding label, and cover it for use.
（2）Prepare ethanol solution of sodium hydroxide: Accurately weigh about 0.4g of NaOH, mix it with a small amount of absolute ethanol, add it to a 100mL volumetric flask, add ethanol to the mark, cover and shake well, and place in In the reagent bottle with the corresponding label, cover it for use, and calculate the concentration of NaOH (moL/L).
（3） Take a conical flask containing a known mass of reaction mixture, add 25mL of hydrochloric acid-acetone solution with a 25mL pipette, cover it, and shake it well to completely dissolve the resin. After standing for 1 hour, add 3 drops of phenolphthalein reagent and titrate with NaOH ethanol solution until the solution turns pink and does not fade within 30 seconds. At the same time, carry out two blank titrations according to the above conditions.
（4） Calculation of epoxy value:
E=(V1-V2)×c÷10m
In the formula, E: epoxy value;
V1: the average volume of NaOH ethanol solution consumed by titrating two blank samples, mL;
V2: the volume of NaOH ethanol solution consumed for titrating the reaction mixture of known mass, mL;
m: mass of the reaction mixture, g.