GB/T 12008.6-2010Plastics -- Polyether polyols -- Part 6: Determination of degree of unsaturation (English PDF)

7.1 Instruments

7.1.1 Pipette: 25 mL.

7.1.2 Conical flask: 250 mL, with a glass stopper.

D---the volume of 0.05 mol/L potassium hydroxide-ethanol standard titration solution consumed by titration of the test portion, expressed in (mL);

E---the volume of 0.05 mol/L potassium hydroxide-ethanol standard titration solution consumed by titration of the blank, expressed in (mL);

N---the concentration of potassium hydroxide-ethanol standard titration solution, expressed in (mol/L);

C---the acidity value of the specimen (calculated as the amount of KOH consumed), expressed in (mg/g);

W---the mass of the test portion, expressed in (g);

56.1---the numerical value of the molar mass of potassium hydroxide, expressed in (g/mol).

7.5 Precision

The difference between parallel results obtained by the same person shall not exceed 0.002.

8.1 Instruments

8.1.1 Pipette: 2 mL.

8.1.2 Automatic titrator: it can determine the acid form end point and is equipped with a 5 mL burette.

8.1.3 Complex, glass and pH electrode for use with the automatic titrator.

8.1.4 Analytical balance: accurate to 0.1 mg.

8.1.5 Titration container: with a capacity of 100 mL.

8.2 Reagents

Unless otherwise stated, only analytically pure reagents are used.

8.2.1 Methanol.

8.2.2 Mercuric acetate-methanol solution: c = 0.05 mol/L.

Dissolve 16 g of mercuric acetate [Hg(C2H3O2)2] in 1 L of methanol solution, add a sufficient amount of glacial acetic acid, so that 2 mL of the reagent blank consumes 0.5 mL ~ 1 mL of

0.05 mol/L potassium hydroxide-methanol standard titration solution. Usually, it is necessary to add a few drops of glacial acetic acid. The solution needs to be weekly prepared and filtered before use.

8.2.3 Potassium hydroxide-methanol standard titration solution: c (KOH) = 0.05 mol/L.

Dissolve potassium hydroxide in methanol to prepare a 0.05 mol/L solution. Use standard potassium hydrogen phthalate for calibration.

8.2.4 Hydrochloric acid-methanol standard titration solution: c (HCl) = 0.05 mol/L.

Add concentrated hydrochloric acid to methanol solution to prepare a 0.05 mol/L solution. This will introduce less than 0.5% water into the reagent. Use 0.05 mol/L potassium hydroxide- methanol standard titration solution for calibration.

8.2.5 Sodium bromide.

8.3 Steps

8.3.1 If it is known that the degree of unsaturation of the specimen is not greater than 0.033 mol/kg, weigh approximately 1 g (accurate to 0.1 mg) of the test portion. If the degree of unsaturation of the specimen is unknown, use 1 g of specimen to determine the approximate value of its degree of unsaturation, and divide 0.033 by the approximate value of the degree of unsaturation of the sample to calculate the required mass of the test portion, expressed in (g).

8.3.2 Add 2 mL of mercuric acetate-methanol solution (8.2.2) and shake it, until the test portion is completely dissolved. Use a watch glass to cover it and let it stand for at least 30 minutes.

Add 50 mL of methanol (8.2.1), then, add 0.25 g of sodium bromide (8.2.5).

8.3.3 On the automatic titrator (8.1.2), use 0.05 mol/L potassium hydroxide-methanol standard

titration solution (8.2.3) to titrate it to the end point.

8.3.4 Without adding any sample, in accordance with the same steps, carry out a blank test.

8.3.5 Without adding mercuric acetate, in accordance with the same steps, prepare the sample, and determine the acidity or alkalinity of the polyol to correct the result. Use 0.05 mol/L potassium hydroxide-methanol standard titration solution to titrate it to the potential end point.

If the solution to be determined has passed the acidity end point, use 0.05 mol/L hydrochloric acid-methanol standard titration solution (8.2.4) and repeat this step to determine the alkalinity.

8.4 Result Calculation and Expression

8.4.1 The acidity A of the specimen, expressed in (mol/kg), shall be calculated in accordance with Formula (2):

Where,

VA---the volume of 0.05 mol/L potassium hydroxide-methanol standard titration solution consumed by neutralization of the test portion, expressed in (mL);

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