HIRANUMA APPLICATION DATA

Resins, Oils andFats, Rubber,Adhesives, Paints

Automatic Titrator

Data No. M1

Apr. 5,
2019

Epoxy equivalent determination ofepoxy resins

1. Abstract
Epoxy resins have competent characteristics such as chemical resistance, heat resistance, and electricalproperties. They are widely used for various materials like sealant of electronic device (IC).
Epoxy resin is generic name of compounds which have two or more epoxy group in one molecule, it does
not harden by itself. The addition of catalyst or hardener is required for curing. It becomes thermoset resin throughaddition polymerization with epoxy group by the hardener (fatty amine etc.). The additive amount of hardenercorresponds to epoxy equivalent (mass of resin including one-equivalent epoxy group) of each epoxy resin. The
determination of epoxy equivalent is quite important process for quality control. The measurement method ofepoxy equivalent is defined in JIS (Japanese Industrial Standards) K7236:2001. Measurement is performed asfollows:1)

Weigh the sample accurately and dissolve it in chloroform.

2)

Add acetic acid and tetraethyl ammonium bromide - acetic acid solution.

3)

Perform potentiometric titration with 0.1 mol/L perchloric acid - acetic acid standard solution.

Perchloric acid reacts with tetraethylammonium bromide and generates hydrogen bromide by addition ofperchloric acid - acetic acid standard solution. (Refer to the reaction formula 1-1.)
The generated hydrogen bromide reacts with epoxy group. (Refer to the reaction formula 1-2.)
When all epoxy groups are reacted and hydrogen bromide gets excess, this point is detected as the endpoint
to determine epoxy equivalent.

(C2H5)4NBr + HClO4 → HBr + (C2H5)4NClO4R－CH－CH2 + HBr → R－CH－CH2OOH・・・(1-1)
・・・(1-2)Br

2. Configuration of instruments and reagents(1) Configuration of instruments
Main unit: Hiranuma Automatic Titrator COM series

Electrodes: Glass electrodeGE-101B: Reference electrodeRE-201Z*Inner solution has to be changed to saturated sodium perchlorate in acetic acid.
(2) Reagents
Titrant: 0.1 mol/L Perchloric acid –acetic acid standard solution

Solvent: 10 mL of chloroform (can be increased up to 30 mL when sample is macromolecule.)
20 mL of acetic acid

Additive: Tetraethylammonium bromide in acetic acid solution
100 g of tetraethylammonium bromide is dissolved in 400 mL of acetic acid.

3. Measurement procedure(1) Take a sample with equivalent amount to 6.0×10-4 ~ 9.0×10-4 mol epoxy group into a 100 mL beaker andweigh accurately to 0.1 mg digits.
*JIS K7236 describes “sample sizes are about 0.1 ~ 0.16 g for 180 ~ 190 epoxy equivalent sample, andabout 0.3 ~ 0.4 g for 450 ~ 500 epoxy equivalent sample, respectively.” in the remark.
(2) Add 10 mL of chloroform and dissolve sample by stirring. It could be gently heated when the sample hasless solubility. In that case, cool it down to room temperature.
(3) Add 20 mL of acetic acid and 10 mL of tetraethylammonium bromide solution(4) Immerse the electrodes and titrate with 0.1 mol/L perchloric acid – acetic acid standard solution.
Additionally, perform the blank test with the same procedure of sample measurement.

4. Measurement conditions and results
Examples of titration conditions
Measurement condition for blank
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT TimerD.P. mL
End Sens
Over mL
Max.Vol.

1Auto
11mV
5000300
0.11sec
mL
sec
mL
mL
mL

ConstantNo.
SizeBlank
Molarity
FactorKL
Unit
FormulaDecimal Places
Auto In Pram.

10 mL
0 mL
0.1 mol/L
1.003
00mL

Mode No.
Pre Int
Del K
Del Sens
Int Time
Int Sens
Brt Speed
Pulse

1500053
280.01

sec
mVsec
mV

mL

D
3None

Measurement condition for sample
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mL
Max.Vol.

2Auto
11mV
5000300
0.320sec
mL
sec
mL
mL
mL

ConstantNo.
2Size0Blank
0.014
Molarity
0.1
Factor
1.003
K1L0Unit
EE
Formula1000*S/((D-B)*M*F*K)
Decimal Places
4
Auto In Pram.

g
mL
mol/L

None

Mode No.
Pre Int
Del K
Del Sens
Int Time
Int Sens
Brt Speed
Pulse

8050532400.05

sec
mV
sec
mV

mL

Measurement results
Measurement of blank

Measurement of sample

Number ofSize

Titrant

Number ofSize

Titrant

Epoxy equivalent

Measurement(g)

Volume (mL)

Measurement(g)

Volume (mL)

(EE)

1-

0.016

10.12076.321

190.8020

2-

0.012

20.1483

7.865

188.3280

30.1218

6.426

189.3880

Avg.
0.014 mL
(Blank)Statisticcalculation

Measurement of blankAvg.

189.51 EE

SD1.24 EE

RSD

0.65 %

Measurement of sample

Examples of titration curves

5. Note(1) Temperature correction of perchloric acid – acetic acid standard solution
Acetic acid used as a solvent for perchloric acid standard solution has a relatively large thermal expansion
coefficient (1.07×10-3). When the temperature of the sample measurement is different from that of factor
titration, multiply the following correction value by titrant factor for the temperature correction in conformity
with the formula in JIS K 7236.
K = 1 – (t - t0) / 1000 … (5-1)
K : Thermal expansion coefficient of titrant
t0 : Temperature at titrant factor determinationt : Temperature at sample titration

(2) Preparation of inner solution for reference electrodeThe inner solution of the reference electrode RE-201Z is filled with saturated KCl aqueous solution whenpurchased. This inner solution have to be replaced to saturated sodium perchlorate in acetic acid solution forthis measurement. Replacement procedure is described below.
i) Prepare the saturated solution of sodium perchlorate in acetic acid with reagent grade of these.
ii) Discharge inner solution from reference electrode RE-201Z and wash inside it with water and then aceticacid.
iii) Fill the prepared inner solution into reference electrode from the supply port.
iv) Leave the electrode for one day before use.
(3) Influence of water contamination on titration
Water contaminated in sample solution could get less sensitivity around the end point. Therefore please takecare not to contaminate sample solution with water.
(4) Samples with less reactivity
JIS K7236:2001 describes that solid tetraethylammonium iodide or 10 % chloroform solution is recommended
instead of tetraethylammonium bromide solution when sample is epoxy-containing product with lessreactivity.
(5) Solvent for sample
According to JIS K7236:2001, chloroform is used as solvent to dissolve sample. When sample ismacromolecule, the volume of chloroform can be increased up to 30 mL to dissolve sample, but the usage ofother solvent is not described there. However, sometimes toluene or dioxane which readily dissolve the sample
are used as solvent instead of chloroform from the aspect of sample solubility.
(6) Washing of electrodes
The residual resin adheres on the electrode after the measurement. Please sufficiently wash it with the solvent
used for this titration.
Keywords: Epoxy equivalent, Epoxy resins, JIS K7236, Perchloric acid titration, Non-aqueous titration,
Tetraethylammonium bromide*Some measurement would not be possible depending on optional configuration of system.