Toluene-2,4-diisocyanate (TDI)

Substance name	Toluene-2,4-diisocyanate
CASR number	584-84-9
Molecular formula	C9H6N2O2
Synonyms	TDI, toluene diisocyanate; 2,4 diisocyanatotoluene; isocyanic acid; methylphenylene ester; 2,4-diisocyanatotoluene, 2,4-tolylene diisocyanate, cresorcinol diisocyanate; 4-methy-1,3-phenylene diisocyanate; toluene 2,4-diisocyanate.

Physical and chemical properties

2,4-Toluene diisocyanate (TDI) is a clear to pale yellow liquid with a sharp pungent odour.

Melting point	12.5-13.5°C
Boiling point	251°C
Specific gravity	1.225
Vapour pressure	6
Flashpoint	121°C

TDI reacts with water, releasing carbon dioxide. It reacts (sometimes violently) with acids, bases, and alcohols.

Common uses TDI is used to manufacture polyurethane products. These are found in the form of coatings, sprays, insulation materials, polyurethane coated fabrics and (the largest application) foam cushioning. It is often used in combination with its isomer, 2,6-TDI (CAS number 91-08-7).

Sources of emissions

Point sources Industrial emissions to air (especially companies producing the materials listed above) or spills.

Diffuse sources, and point sources included in aggregated emissions data Emission to air (by outgassing) from products containing TDI.

Natural sources There are no known or expected natural sources of TDI emissions.

Mobile sources There are no significant mobile emission sources.

Consumer products that may contain toluene-2,4-diisocyanate Products include polyurethane coatings, cement sealers, polyurethane mastic sealants, and polyurethane cushions and pads. Very low emissions of TDI have been infrequently detected from cushions.

Health effects

How might I be exposed to TDI? Exposure to TDI can occur in workplaces manufacturing TDI or using TDI in production, or in the environment following releases to the air. Consumers can be contaminated when they misuse certain polyurethane coatings, sealers, polyurethane foam kits, or sealants. Exposure can occur through skin contact and also from working with TDI or misusing consumer products containing TDI.

By what pathways might TDI enter my body? TDI can be breathed in if there has been a commercial discharge or a spill, or the misuse of consumer products containing TDI.

Health guidelines National Occupational Health and Safety Commission (NOHSC):

• TWA (eight-hour time weighted average) exposure limit in the workplace: 0.02 mg/m³.
• STEL (short-term exposure limit) (15 minutes): 0.07 mg/m³.

TDI is listed as a sensitiser. Under the National Model Regulations for the Control of Workplace Hazardous Substances, isocyanates require health surveillance.

A concentration 10-20 times the level of the exposure standard would be needed before TDI could be detected by its odour.

What effect might TDI have on my health? TDI is irritating to the eyes, respiratory system and skin; it is toxic from both short-term and long-term exposures. Single large inhaled doses can cause severe irritation of the respiratory, gastrointestinal and central nervous systems. High levels can cause build-up of fluids in the lungs, which could lead to death. Exposure can cause lung allergy, after which future low-level exposures can trigger shortness of breath.

Long-term exposures (chronic exposures) have resulted in significant decreases in lung function in workers, in asthma-like reactions, and in effects on the liver, blood and kidneys. The International Agency for Research on Cancer has classified TDI as a 'possible human carcinogen'.

Environmental effects

Environmental fate TDI reacts quickly with water and other photochemically produced materials, so most of it will be out of the atmosphere in less than two days.

Environmental transport TDI quickly reacts with water, so it will not accumulate in the environment.

Environmental guidelines There are no national guidelines.

What effect might TDI have on the environment? TDI has slight acute (short-term) toxicity to aquatic life and high acute toxicity to birds. There is not enough information to predict or evaluate the long-term effects of TDI on plants and animals.