TDI and MDI Are Making Our Lives Easier

What Are Diisocyanates?

There are two main aromatic diisocyanates; toluene diisocyanate (TDI) and methylene diphenyl diisocyanate (MDI). Diisocyanates are a family of chemical building blocks fundamentally used to produce polyurethane products such as rigid and flexible foams, coatings, adhesives, sealants and elastomers. Every day, many products you can rely on are produced in a safer and more comfortable form thanks to polyurethanes provided by diisocyanates. Polyurethane chemistry is complex, but understanding the basics is quite straightforward. Polyurethanes are produced by combining diisocyanates with polyols and other chemical additives. Various diisocyanates and a wide range of polyols can be used to produce polyurethane and the reaction speed can be adjusted, allowing a broad range of materials to be produced to meet specific application requirements.

Diisocyanates are particularly important in the production of numerous products, especially in the transportation and construction industries. Diisocyanates used in polyurethane production are divided into two types; aromatic diisocyanates and aliphatic diisocyanates. Aromatic Diisocyanates

The two main aromatic diisocyanates consist of toluene diisocyanate (TDI) and methylene diphenyl diisocyanate (MDI). TDI is primarily used in flexible foam production. MDI is the second type of DII: it comes in two forms, pure MDI and polymeric MDI (PMDI). Pure MDI is used in the production of various polyurethane products such as elastomers, sealants, adhesives and coatings. PMDI is a versatile product used to produce a wide range of rigid, flexible, semi-rigid and polyisocyanurate and thermoset foams. Less common aromatic diisocyanates such as p-phenylene diisocyanate (PPDI) and naphthalene diisocyanate (NDI) also exist.

What Is TDI?

Toluene diisocyanate (TDI) is a chemical used predominantly in polyurethane production for flexible foam applications such as furniture, bedding and carpet underlay, as well as for packaging applications. TDI is also used in coatings, sealants, adhesives and elastomers. In transportation applications, TDI helps produce lighter vehicle parts and thereby provides weight savings that lead to improvements in fuel efficiency and consequently energy savings. From a technical standpoint, TDI is obtained by nitration of toluene. Subsequently, hydrogenation of dinitrotoluene is carried out to produce toluenediamine (TDA); this is then reacted with phosgene to form TDI.

What Is MDI?

Methylene diphenyl diisocyanate (MDI) is a chemical used in polyurethane production for many applications. MDI is used primarily in the production of rigid polyurethane foams used for insulation in your home or refrigerator and in many other areas. Insulation made with MDI can help consumers save on heating and cooling costs and make energy savings. Some additional uses of MDI in polyurethanes include coatings, adhesives, sealants and elastomers found in substances such as paints, adhesives and weather-resistant materials. It is also used in making many types of shoes, sports and recreational products and to a lesser extent in producing certain specialty flexible foams. MDI can also be used as a binder for wood and for producing mold cores for the foundry industry. From a technical perspective, MDI is obtained from the condensation of formaldehyde with aniline to produce methylene dianiline (MDA); this is then reacted with phosgene to form MDI.

What Are Aliphatic Diisocyanates?

Diisocyanates, including a specific subgroup referred to as aliphatic diisocyanates, have been used since the late 1940s and have been extensively studied. Aliphatic diisocyanates such as hexamethylene diisocyanate (HDI), methylene dicyclohexyl diisocyanate or hydrogenated MDI (HMDI) and isophorone diisocyanate (IPDI) are typically reacted to form polyisocyanates that function as building blocks in creating colour-stable polyurethane coatings and elastomers. Diisocyanates (DII) are used to make various polyurethane (PU) products found in your automobile. DII chemistry enables many of the features you enjoy in your vehicle. Polyurethanes not only help improve automobile design, but also help make vehicles stronger, lighter, safer and more comfortable.

What Is the Contribution of DII Chemistry?

Many of the vehicle parts produced with polyurethane products typically based on DII chemistry contribute to a more enjoyable driving experience. Armrests made from foam, headrests, acoustic insulation for quieter driving, cup holders and "soft-touch" PU coatings on interior components such as instrument panels are among the examples. Steering wheels, gear shift knobs, floor carpeting, carpet underlay and interior linings can also use polyurethanes to enhance their performance and feel. DII chemistry also contributes to many of the functional needs of the automobile, including light door panels, bumpers, exterior panels, coatings and adhesives, cable jacket protection, brake lines, seals, window seals, shock absorbers or spring helpers and rubber fillers for fastening.

If you drive a pickup truck, you will see that there is a very high likelihood that the truck bed liner and tailgate are produced with polyurethane products. Some Examples: Automotive Applications

* Fibre-reinforced polyurethanes can be used for light body panels. * Seat frames made from moulded PU foams can be 35 percent lighter than metal-pressed frames. * Polyurethanes help protect passengers by absorbing energy in door and head impact areas. * Typically 10-15 kg of foam is used in vehicle seats. Seating foams are on average 50 percent thinner compared to a few years ago and their design is continually improved to provide more comfort. Thinner seats not only provide lightness but also more interior space without raising the vehicle roof height. * Rear seats in minivans and SUVs can consist of hard PU foam with cast foam covering and this foam has the characteristics of being light and strong. * Polyurethane "soft-touch" skins help significantly reduce the weight of instrument panels. These PU coatings also provide protection against the sun's harsh UV rays while offering comfort and quality on door panels, steering wheels, headrests and armrest areas. * Load-bearing floor composites combining a honeycomb structural matrix with polyurethane can create lighter and stronger parts than many other technologies. * Polyurethane and epoxy systems also using DII chemistry are used in body fascia (e.g. grille, headlamp area) and bumpers due to good strength-to-weight ratio. These parts are mostly produced with polyurethanes using the Reaction Injection Moulding (RIM) technique. * Polyurethane foam can be used as light technology for attaching wheel covering to aluminium hub. * Quilted, carpet underlay and other interior insulation materials are made lighter with polyurethane technology while meeting the expected noise reduction requirements for quiet driving.

Use for Insulation in Residential Buildings

According to the U.S. Department of Energy (DOE), heating and cooling account for approximately 56 percent of energy use in a typical U.S. home and the largest energy expenditure for most homes. With rising energy costs, there is increasing interest in making homes and buildings more energy efficient. Methylene diphenyl diisocyanate (MDI) is used to produce rigid polyurethane, spray polyurethane foam and polyiso (PIR) foam insulation used in residential and commercial buildings.

Types of Foam Insulation

MDI is used to make varieties of foam insulation products: * Laminated panels with flexible facing and board stock commonly used for commercial roof decking. * Metal-faced panels used for the exterior cladding of commercial buildings. * Structural insulated panels (SIPs) used in floors, walls and roofs in residential and light commercial buildings. * Rigid board and bunstock used especially for commercial and industrial applications. * Spray polyurethane foam for a wide variety of residential and commercial uses including walls, ceilings and roof systems. * Single-component insulation foam used as a filler sealant and adhesive for Do-It-Yourself (DIY) and professional use.

Advantages of Foam Insulation

Foam insulation is a popular choice because it can help you lower your energy bills. How? To put it simply, when the air in your home is heated or cooled, foam insulation helps effectively seal gaps and prevent leaks. Insulation helps prevent outside air from entering and inside air from escaping. This creates a comfortable environment in your home while at the same time reducing your energy consumption. Foam insulation products are typically used for both walls, attics, floors and roof covering systems in new construction and renovation projects. These products are not only commonly used for insulation and air sealing but can also help reduce noise and moisture by preventing mould and mildew formation. Spray polyurethane foam, which typically has a high R-value, can be sprayed directly into voids, cracks and other surfaces that can cause air leakage, resulting in heating or cooling loss. Because it is sprayed in place, it has the ability to contour to different shapes before hardening, thus providing a high level of air sealing performance for air conditioning and insulation projects.