Methylene Diphenyl Diisocyanate (MDI)
MDI is used almost exclusively to make polyurethanes. Polyurethanes are produced by reacting diisocyanates, in this case MDI, with polyols and other chemicals. It is an exothermic reaction, as it releases heat. MDI-based rigid urethane foams have the lowest thermal conductivity of any common insulation material. The largest insulation uses for these foams are in construction, refrigerators and freezers, and refrigerated rail cars and trucks. Rigid foams also have excellent buoyancy and have been used in life-saving gear, swimming pools, sporting goods, and other flotation devices. MDI is also used in composite wood products, adhesives, coatings, elastomers, and footwear.
In some industries, such as the appliance industry, TDI-based materials are being replaced by MDI-based polyurethane insulation. MDI’s advantages include lower vapor pressure and faster cure rates and cycles. Some coating, adhesive, and elastomer applications have also been replacing TDI with MDI.