The main use for methyl di-p-phenylene isocyanate (MDI) is in the production of rigid and semi-rigid polyurethane foams, which accounts for some 80% of global consumption. The majority is used in the construction industry. MDI is supplied as a mixture of polymeric isocyanates, the dimer and trimer (PMDI), and in its pure form. This is not the blended form known as systems. Pure MDI (as reported by ICIS pricing) is distilled from the mixture and is used in reaction injection moulding (RIM), thermoplastic elastomers and adhesives.
Applications for MDI also include construction, refrigeration, packaging, tank and pipe insulation, and other foam uses, including transportation, marine flotation and furniture where its good insulating properties are utilised. In marine uses, rigid foam has superior buoyancy in addition to providing insulation. PMDI is also used a foundry core binder resin. RIM products are used in automobile parts to produce fascias, bumpers and other body parts.
Pure MDI occurs as white to pale yellow crystals or flakes with a slightly musty odour.
The major outlet for toluene di-isocyanate (TDI) is in the manufacture of flexible polyurethane foam for use in furniture, buildings and transportation. Other outlets include rigid foams and adhesives, as a cross-linking agent for nylon 6; as a chemical intermediate in the manufacture of polyurethane coatings in floor and wood finishes and sealers, paints, concrete sealers, for aircraft and tank trucks as well as in the manufacture of polyurethane elastomers in coated fabrics and clay pipe seals. Polyurethane elastomers, produced by the reaction of TDI with short-chain polyols, can be used in the manufacture of polyurethane fibres.
TDI occurs as colourless to pale yellow liquid or crystals with a pungent odour. It turns pale yellow on exposure to air and is soluble in aromatic and chlorinated aromatic hydrocarbons, ether, acetone, and esters. It reacts with water, ammonia and alcohols with the evolution of carbon dioxide and oxidising agents.
All isocyanates are toxic and harmful through inhalation, ingestion or skin contact.
ICIS pricing quotes Isocyanates in Europe, Asia-Pacific, China, USA and the Middle East.
To find out more Isocyanates Methodology April 2013