MIL-PRF-23942A(AS)
c. Magnetic stirrer.
4.5.5.2 Reagents and materials.
a. Foil.
b. Nitrogen.
c. Pyridine, reagent grade.
d. Sodium methylate, standard, 0.2 normal (N). Dissolve 4.6 grams (g) of clean metallic
sodium in reagent grade methanol and dilute to one liter with the same solvent. Standardize
against standard 0.1N HCl using thymol blue indicator.
e. Sodium methylate, 0.02N standard. Dilute 100.0 mL of the 0.2N standardized sodium
methylate to exactly one liter with methanol.
f. Thymol blue indicator. Dissolve 0.3 g thymol blue in 100 mL of methanol.
4.5.5.3 Procedure.
4.5.5.3.1 Test specimen preparation. Weigh, in duplicate, 0.4 to 0.6 g of polymer sample
into a previously tared 250 mL Erlenmeyer flask (see 6.4.1). Add 50 mL of pyridine and a
magnetic stirring bar. Cover the flask with foil to help exclude atmospheric carbon dioxide and
dissolve the sample by stirring magnetically.
4.5.5.3.2 Titration. Insert the sodium methylate buret tip and the nitrogen flush tube into the
flask by puncturing the foil. Flush the flask with nitrogen, and maintain a slow flow of nitrogen
into the flask during the titration. Add ten drops of thymol blue solution and titrate to a blue end
point with 0.02N sodium methylate solution prepared above. Repeat the titration procedure using
50 mL of pyridine as a blank.
4.5.5.4 Calculations. Carboxyl content shall be calculated as follows:
Carboxyl content, wt. percent = (A-B) (N) (45.02) X 100
(1,000)W
Where:
A = mL of sodium methylate required for sample.
B = mL of sodium methylate required for blank.
N = Normality of sodium methylate.
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