GB/T 12009.4-2016 in English

Determination of isocyanate content in aromatic isocyanates used in the production of plastic polyurethane

1. Standard background and technology evolution analysis

GB/T 12009.4-2016 is the national standard of the People's Republic of China, which is used to determine the isocyanate content in aromatic isocyanates used in the production of plastic polyurethane. This standard replaces the old version from 1989 and introduces many technical improvements, including:

• Added description of interference factors
• Optimized sampling method and test conditions
• Modified reagent usage specifications
• Introduced new titration method

2. Method Overview

This standard provides two methods for determining isocyanate content:

1. Method A: Toluene/di-n-butylamine and hydrochloric acid standard titration solution method
2. Method B: Toluene/trichlorobenzene and hydrochloric acid-methanol standard titration solution method

3. Detailed explanation of Method A

Principle:Isocyanate sample reacts with excess di-n-butylamine in toluene to form substituted urea, which is then back-titrated with hydrochloric acid standard titration solution.

Procedure of Method A

1. Weigh the sample and add di-n-butylamine solution.
2. After the reaction, dilute with acetone.
3. Determine the excess di-n-butylamine by potentiometric titration or colorimetric titration.

4. Detailed explanation of Method B

Principle:Isocyanate sample reacts with excess di-n-butylamine in toluene/trichlorobenzene solvent to form substituted urea, which is then back-titrated with hydrochloric acid-methanol standard titration solution.

Procedure of Method B

1. Weigh the sample and add di-n-butylamine solution and trichlorobenzene.
2. After the reaction, dilute with methanol.
3. Determine the excess di-n-butylamine by potentiometric titration or colorimetric titration.

5. Implementation recommendations

Choose a method:

• Preferably use method A because it is more accurate and suitable for refined products.
• For crude or modified isocyanates, method B is recommended.

Notes:

• The relative humidity in the laboratory should not exceed 60%.
• Pay attention to the sealed storage and rapid sampling of samples to prevent reaction with moisture in the air.
• The concentration and volume of hydrochloric acid must be accurately controlled during the titration.