How Are Isocyanates Used?

TDI is a combination of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate. TDI is usually found in an 80:20 mixture of these two forms. TDI is used in the manufacture of flexible foam used in a variety of products, including:

• mattresses
• upholstery cushions
• automobile seats
• packaging materials

   MDI has replaced TDI in the production of rigid foams because it is less hazardous due to its lower volatility (its ability to produce a vapour). Rigid foam is used as insulation in home refrigerators and ovens, while spray-in foam is used for railroad cars, truck trailers, and boats. MDI is used as part of a no-bake binder system for casting moulds in foundries.

   As protective coatings, polyurethanes are applied to electrical wiring because they are good insulators. They are used as two-part paints and floor, concrete and wood finishes where their hardness and durability are important. Aircraft, truck and other coatings are often composed of diisocyanate prepolymer systems. Isocyanates are also used as adhesives and elastomers in automobile bumpers, printing rolls, liners for mine and grain elevator chutes, shoe soles, coated fabrics, and spandex fibres.

   When making polyurethane foams, isocyanate (part A) is usually added to polyether or polyester polyols (part B or resin) along with fire-retarding agents, catalysts and blowing agents (part B) to form polyurethane. Adding water creates carbon dioxide gas followed by foam production. If water is not added, the polyurethane mixture can be used as a coating material.

   Commercially, polyurethane adhesives and coatings may be available as two-component systems that react together and must be mixed just prior to use or as one-component systems that require reaction with oxygen or moisture after application for curing.

Occupational Exposures (See Reference #6) adhesive workers aircraft builders appliance makers boat makers cushion makers foam makers insulation workers isocyanate workers lacquer workers life preserver makers mine tunnel coaters painters plastic foam makers plastic moulders polyurethane foam makers rubber workers ship builders ship welders textile processors upholstery workers varnishers wire-coating workers