Toluene diisocyanate (TDI) 80/20

Toluene diisocyanate (TDI) 80/20 is a mixture of two isomeric forms of toluene diisocyanate. The molecules of the compounds are each made up of a component, toluene, and two residual groups of isocyanic acid, with the two isomers differing in their spatial arrangement.

The center of the compound is formed by a cyclic, unsaturated hydrocarbon group with six carbon atoms. The methyl group of toluene is located on one of the carbon atoms of the ring structure, while one of the two isocyanic acid residues is attached to an adjacent carbon atom. If there are isocyanic acid residues on both sides of the methyl group, it is toluene-2,6-diisocyanate. The molecules of the isomeric compound toluene-2,4-diisocyanate, on the other hand, have a second isocyanic acid residue, which is attached exactly opposite the methyl group.

Toluene diisocyanate (TDI) 80/20 consists of 80% toluene-2,4-diisocyanate and 20% toluene-2,6-diisocyanate. In addition to this common mixture, toluene diisocyanate is also used commercially in other mixing ratios such as toluene diisocyanate 65/35 or as pure toluene-2,4-diisocyanate.

Under normal ambient conditions, toluene diisocyanate (TDI) 80/20 is a colorless to yellowish liquid with a pungent odor. The melting point of the hardly volatile mixture is below a temperature of 20 °C, so even a slight cooling leads to the solidification of the substance. This can lead to the separation of the two isomeric components, since they have slightly different physical properties. The compounds go into the gaseous state when heated to 251 °C.

Toluene diisocyanate (TDI) 80/20 is not soluble in water as the substances decompose in water. In contrast, the mixture is readily soluble in many organic solvents such as ethanol, diethyl ether, ethyl acetate, carbon tetrachloride, acetone and benzene.

Toluene diisocyanate (TDI) 80/20 is an extremely reactive mixture of substances. It decomposes on contact with moisture or water. This produces gaseous carbon dioxide, so that the resulting excess pressure can cause closed containers to burst. The mixture must also be protected from heat and light. Polymerization of the substances can occur in the presence of bases. With alcohols, amines, acids and strong oxidizing agents there is a risk of violent reactions with a strong temperature development. When storing toluene diisocyanate, it should be noted that the mixture of substances will attack containers made of copper and aluminum.

Toluene diisocyanate is flammable but difficult to ignite. However, the vapors of the liquid can form highly flammable and explosive vapor-air mixtures with the ambient air. Open containers of the substance should therefore be kept away from possible sources of ignition such as open flames, sparks, electrostatic charges and hot surfaces. Irritant and toxic gases are produced when toluene diisocyanate (TDI) 80/20 is burned. Among other things, dangerous isocyanates, nitrogen oxides and carbon monoxide are released.

Toluene diisocyanate (TDI) 80/20 poses acute and chronic health hazards. The mixture of substances is toxic, irritating to the skin and possibly carcinogenic. The liquid causes severe irritation, persistent sensitization and allergic skin reactions. Contact with the mixture of substances also causes severe eye irritation. Persistent impairment of vision is possible. After exposure, the skin should be washed thoroughly with soap and water, and an affected eye should be gently rinsed under running water. Subsequently, medical treatment is required.

Inhaling and swallowing toluene diisocyanate is fatal. If an odor can be detected, this already indicates a concentration that is harmful to health.

Due to long-term damage to aquatic organisms, Toluene Diisocyanate (TDI) 80/20 has been classified as clearly hazardous to water. The substance mixture must not get into water bodies, the soil or waste water. Any escape into the environment must be reported to the relevant authorities. Special regulations apply to the transport of toluene diisocyanate.