This standard specifies the method for determining epoxy equivalent. This method is applicable to all epoxy compounds; for epoxyamines, the modified method specified in Appendix A (Supplement) needs to be used. GB 4612-1984 Determination of epoxy equivalent of epoxy compounds GB4612-1984 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Epoxide compoundswwW.bzxz.Net
Determination of epoxide equivalent This standard is equivalent to ISO3001-1978 "Scope of application of plastics
Epoxide compounds
UDC 678.686
GB 4612 --84
Determination of epoxide equivalent"
This standard specifies the method for determining epoxide equivalent. This method is applicable to all epoxy compounds; for epoxyamines, the modified method specified in Appendix A (Supplement) is required. 2 Definition
Epoxide equivalent: The mass of a substance containing ... gram molecules of epoxy groups (grams). 3 Principle
Based on the reaction of nascent hydrogen bromide generated by the action of 0.1N perchloric acid standard titration solution and tetraethylammonium bromide with epoxy groups. Use crystal violet as an indicator, or use potentiometric titration for dark products to determine the endpoint. 4 Reagents
Use only recognized analytically pure reagents during the analysis. 4.1 Glacial acetic acid.
4.2 Acetic acid f.
Methyl chloride.
4.4 Potassium hydrogen benzoate.
4.5 Crystal violet indicator solution: Dissolve 100 mg of crystal violet in 100 ml of glacial acetic acid. 4.6 Perchloric acid: 0.1N standard titrant.
4.6.1 Preparation
Add 300 ml of glacial acetic acid to 8.5 ml of 70% (mass/mass) perchloric acid aqueous solution, add 20 ml of acetic anhydride, dilute to 1 liter with glacial acetic acid and mix thoroughly.
4.6.2 Calibration
Use 200.0 mg of potassium hydrogen phthalate dissolved in 50 ml of glacial acetic acid to calibrate the perchloric acid solution (potassium hydrogen phthalate should be dried at 120℃ for 2 hours before use), use 4 to 6 drops of crystal violet solution as an indicator, and perform endpoint titration until a stable green color is obtained. Note the temperature t of the standard titrant.
Note: ① If the epoxy equivalent is determined by potentiometric titration, the same method should be used to calibrate the perchloric acid. ② It is recommended to use safety goggles and a safety net. 4.6.3 Concentration calculation
The perchloric acid equivalent concentration N is calculated according to formula (1): N
National Bureau of Standards Issued on July 30, 1984
V×0.20422
Implementation on May 1, 1985
GB 4612-84
Formula: m—
1 The mass of potassium hydrogen benzoate used, g; 1 The volume of perchloric acid solution consumed during titration, ml; 1 The number of grams of potassium hydrogen benzoate per milligram equivalent. 0.20422—
4.7 Tetraethylammonium bromide reagent solution: Dissolve 100 g of tetraethylammonium bromide in 400 ml of glacial acetic acid. Add a few drops of crystal violet indicator solution. If the solution changes color, use perchloric acid standard solution to restore it to its original color. Note: For 1 low-activity epoxides, tetrabutylammonium iodide can be used, either as a solid or as a 10% chloroform solution. In this case, it should be kept away from light as much as possible. The chloroform solution of tetrabutylammonium iodide is unstable and must be prepared afresh for each titration. 5 Instruments
5.1 Balance: Sensitivity 0.1 mg.
5.2 Conical flask: 100 or 200 ml, with ground-mouth stopper. 5.3 Burette: Microburette with sealed reservoir or calibrated burette with a capacity of 10 ml. 5.4 Glassware: With ground-mouth joints, the outlet is protected from moisture by a calcium chloride tube. 5.5 Magnetic stirrer: A stirring rod coated with polytetrafluoroethylene should be attached. 5.6 Thermometer: Calibrated, measuring accuracy ±0.1°C. 5.7 Pipette: Maximum capacity is 10 ml.
6 Steps
Weigh a sample containing 0.6 to 0.9 mg of epoxy compound (accurate to 0.2 mg, which is equivalent to a mass between 0.6 and 0.9 × EE mg, where EE is the estimated epoxy equivalent) and place it in a flask. Add 10 ml of chloroform and stir to dissolve the sample. If necessary, slightly heat it. Cool to room temperature, add 20 ml of glacial acetic acid, then add 10 ml of tetraethylammonium bromide reagent solution with a pipette, and add 4 to 6 drops of crystal violet indicator solution. Immediately titrate with perchloric acid solution while stirring with a magnetic stirrer until a stable green color is obtained. Note the temperature t of the perchloric acid solution. At the same time, perform a rate white test without a sample.
7 Representation of results
The epoxy equivalent EE expressed in grams per gram of f is calculated according to formula (2): EE=
Formula t: m-
mass of sample, g;
1000×m
(Vi-Vo)(1
-volume of perchloric acid solution consumed in blank test, ml, volume of perchloric acid solution consumed in determination, ml,-temperature of perchloric acid solution during determination, ℃; t. temperature of solution when calibrating perchloric acid solution, ℃,-equivalent concentration of perchloric acid solution (usually 0.1N). N
Note: It is necessary to use the correction factor because the expansion coefficient of perchloric acid solution is large (1.07×10-7℃=\), which is equivalent to a volume change of 1.07×10-7℃ per degree Celsius. 0.1%. This factor can be avoided if the operation is carried out in a temperature-controlled room. The result is sometimes expressed as the epoxy index, expressed in grams of epoxy compounds per gram of dry substance. It is expressed as follows: Epoxy index
(3)
Test report
The test report should include the following items:
Identification of the sample,
Epoxy equivalent,
GB4612—84
If tetraethylammonium bromide reagent is not used, what reagent is used and any other factors that may affect the results should be stated. A.1 Scope of application
GB 4612--84
Appendix A
Corrected method for epoxyamines
(Supplement)
When nitrogen-containing epoxy resins are determined according to the method described in the main text of this standard, the measured value of the epoxy equivalent is too low. This is due to the reaction between perchloric acid and amino nitrogen, which leads to the formation of a salt. If the perchloric acid included in the salt formed is taken into account, this standard can also be used to determine the epoxy equivalent of epoxyamines. A.2 Principle
The amino nitrogen in the epoxyamine is titrated with a 0.1N perchloric acid standard titrant. The second blank value thus obtained is used to correct the epoxy equivalent calculated according to A, 4.
A.3 Procedure
Determine the second blank value according to Chapter 6 of this standard, but without adding tetraethyl bromide. Ammonium solution. A. Expression of results
Express the epoxy equivalent EE of epoxyamine in grams per gram molecule and calculate it according to the following formula: EE=
(Vi-V.-V)
1000×m
Wherein: m1—the amount of sample used in the second blank test, grams, t-ts
Va—the volume of perchloric acid solution consumed in the second blank test, milliliters. Other symbols have the same meanings as those in Chapter 7 of this standard. Additional notes:
This standard was proposed by the Ministry of Chemical Industry of the People's Republic of China and is under the technical jurisdiction of the Chemical Method Branch of the National Technical Committee for Plastics Standardization
This standard was drafted by Shanghai Resin Factory. The main drafters of this standard are Li Boqing, Bao Limin and Wu Rongdong. 697
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