This standard is applicable to the determination of the acid value of unsaturated polyesters. When free anhydride exists in the resin, the measured value will be slightly lower than the theoretical value due to the formation of carboxylic acid ester precipitation that cannot be measured. GB 2895-1982 Determination of the acid value of unsaturated polyester resins GB2895-1982 standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Determination for acid yalue of unsaturated polyester resinsUDC 678.674
:543.241.5
GB 2895 --82
(1989)
This standard is applicable to the determination of the acid value of unsaturated polyester resins. When free anhydride exists in the resin, the measured value will be slightly lower than the theoretical value due to the formation of carboxylic acid ester precipitation that cannot be measured. DefinitionWww.bzxZ.net
Acid value: the number of milligrams of potassium hydroxide required to neutralize 1 gram of sample under the test conditions. Principle of the method
This method is to dissolve a certain amount of resin sample in a mixed solution, use thymol blue as an indicator, and titrate with potassium hydroxide ethanol standard solution until blue appears, and obtain the acid value based on the consumption of the titrant. 1 Equipment
Analytical balance: sensitivity 0.1 mg,
1.2 Erlenmeyer flask: 250 ml, wide mouth,1.3 Burette: 25 ml, graduation value 0.05 ml1.4 Magnetic stirrer:
1.5 Nitrogen bottle;
1.6 Pipette: 50 ml.
2 Reagents
2.1 Toluene-anhydrous ethanol mixed solvent: 2:1 (volume ratio), 2.2 Thymol blue indicator solution: 0.1% anhydrous ethanol solution, 2.3 Potassium hydroxide standard solution: 0.1N anhydrous ethanol standard solution, 2.4 Acetone: water content less than 0.1%.
Note: ① Preparation and calibration of potassium hydroxide standard solution: refer to GB601-77 "Standard Solution Preparation Method". ② It is recommended to dry analytical pure acetone with phosphorus pentoxide, then distill at atmospheric pressure and receive the stable boiling point fraction. The water content of acetone can be less than 0.1%. 3 Operation steps
3.1 Weigh 0.5-3 g of sample, accurate to 1 mg, and place it in a conical flask. The amount of sample depends on the expected acid value. Use a pipette to draw 50 ml of mixed solvent, add it to the conical flask, and shake until the sample is completely dissolved. If the sample is not completely dissolved, a condenser can be installed on the conical flask and placed in a water bath to warm it. If the solubility is poor and it cannot be completely dissolved within 5 minutes, the sample should be weighed again and dissolved in a new mixed solvent consisting of 50 ml of mixed solvent and 25 ml of acetone. This situation should be noted in the test report. Cool the solution to room temperature, add 5 drops of thymol blue indicator solution, put the conical flask on a magnetic stirrer and pass nitrogen to bubble the solution. Titrate with potassium hydroxide standard solution until the blue color can be maintained for 20-30 seconds without disappearing, which is the end point. Record the number of milliliters of potassium hydroxide standard solution consumed.
3.2 Carry out blank test with corresponding mixed solvent and record the milliliters of potassium hydroxide standard solution consumed. , Calculation and Expression of Results
4.1 Calculation
Published by the State Administration of Standardization on February 8, 1982
Marked by Industry Miscellaneous Band
Implementation on October 1, 1982
The acid value of each test is calculated as follows:
Where: Av-
Acid value of the sample;
GB 2895-82
(V,-V2)T
Ay = 56.1
-The milliliters of potassium hydroxide standard solution consumed by the sample during titration; V2——The milliliters of potassium hydroxide standard solution consumed by the blank test during titration: TThe equivalent concentration of potassium hydroxide standard solution
M——The weight of the sample, grams.
4.2 Result Expression
The test result shall be expressed as the arithmetic mean of the test values ​​of at least two parallel samples, rounded to an integer. Additional Notes:
This standard was proposed by the Ministry of Chemical Industry of the People's Republic of China and is under the jurisdiction of Chenguang Chemical Research Institute. This standard was drafted by Chenguang Chemical Research Institute. The main drafter of this standard is Yang Hejun.
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