GB/T 32471-2016Plastics - Determination of the isomer ratio in toluene diisocyanates for use in the production of polyurethanes (English PDF)

2.1 Principles

This method is based on the non-horizontal distortion (carbon) of the CH bond on the benzene ring at 810 cm-1 and 782 cm-1 of 2,4-TDI and 2,6-TDI Hydrogen bond) caused by the quantitative absorption of infrared light, the two infrared characteristic wavelength light absorption intensity ratio, the preparation of the standard song

Line to determine the mass ratio of 2,4-TDI and 2,6-TDI to obtain the isomer ratio of the sample.

2.2 Test Precautions

Because TDI is easy to react with moisture in the air, special attention should be paid to sample preparation. The usual sampling method (for example, in an open container

Even if the sampling speed is very fast, can also cause the sample to produce insoluble urea, so always use dry inert gas (such as nitrogen, argon)

A closed sampler may be used on the production line or on conditions permitting.

2.3 Reagents

This method uses the following reagents.

a) cyclohexane. analytical grade, before use with 4A molecular sieve to remove water for more than 24 hours;

b) 2,4-TDI. reference reagent, crystallization point 22.0 ° C, refractive index (n20D) 1.56781, density (20 ° C) 1.2186 g/cm 3;

c) 2,6-TDI. Reference reagent, crystallization point 18.2 ° C, refractive index (n20D) 1.57111, density (20 ° C) 1.2270 g/cm 3. Determination

80/20-TDI isomerization, the 2,6-TDI reference can be replaced with a 65/35-TDI high purity reagent (crystallization point 8.0 ° C) d) nitrogen. dew point below -60 ° C.

Note. As the isocyanate easily react with moisture, and exposed to the air easily yellow, it is generally filled with nitrogen (dew point <= -60 °C) sealed storage.

2.4 Instruments

This method uses the following instruments.

a) Infrared spectrophotometer. Fourier infrared spectrophotometer, the accuracy of 0.2%;

b) liquid infrared absorption cell.

1) Test Method A. 0.2 mm sodium chloride or potassium bromide window liquid liquid infrared absorption cell;

2) Test method B. 0.1 mm sodium chloride or potassium bromide window liquid liquid infrared absorption cell.