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What Is The Difference Between MDI And TDI?

Views: 291     Author: Vickey     Publish Time: 2023-07-10      Origin: Site


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What Is The Difference Between MDI And TDI?

Introduction of TDI

The chemical formula of toluene diisocyanate (TDI), an organic substance, is CH3C6H3(NCO)2. Commercially significant isomers include 2,4-TDI and 2,6-TDI , two of the six potential isomers. Although 2,4-TDI is synthesized in its pure form, it is frequently sold as blends of the 2,4 and 2,6 isomers, respectively, in the 80/20 and 65/35 ratios. All TDI isomers are colorless, while commercial examples can have a yellow tint.Polyurethanes are produced using toluene diisocyanate (TDI), particularly for flexible foam applications such as bedding and furniture, carpet underlay, and packaging.

Introduction of MDI

An aromatic diisocyanate is methylene diphenyl diisocyanate (MDI). There are three common isomers: 2,2′-MDI, 2,4′-MDI, and 4,4′-MDI. These are distinguished by the locations of the isocyanate groups around the rings.The most common isomer, commonly known as 4,4′-diphenylmethane diisocyanate, is the 4,4′ isomer. Another name for this isomer is pure MDI. When making polyurethane, MDI interacts with polyols.Polyurethanes are made using methylenediphenyl diisocyanate (MDI), which has a variety of uses, including the creation of hard polyurethane foams for refrigerators and house insulation. Customers who use insulation created with MDI can save energy.

Differences between TDI and MDI

Although both TDI and MDI are types of raw materials used in the manufacturing of polyurethane and can partially replace one another, there are significant distinctions between TDI and MDI in terms of structure, functionality, and subdivision usage.

1.Compared to MDI, TDI has a greater isocyanate concentration and a higher foaming volume per unit mass. Toluene diisocyanate, with its two isocyanate groups on a single benzene ring, and diphenylmethane diisocyanate, with its two benzene rings, are the two compounds that make up TDI and MDI, respectively. In general, the higher the isocyanate content, the greater the unit foaming volume, so when comparing the two, the TDI unit mass foaming volume is larger.

2. The MDI system is rapidly aging. When compared to TDI, the MDI method offers a quick molding cycle, quick cure speed, and superior foam performance.For instance, TDI-based foam typically requires a 12- to 24-hour curing procedure to attain optimal performance, but MDI systems simply require 1 hour of maturity at 95%.

3. It is simple to create diverse foam products with high relative densities using MDI. It can create products with a wide range of hardness by adjusting the mix of components.

4. MDI is not as harmful as TDI, which is quite poisonous. While TDI has a high vapor pressure, is easily volatilized, has a strong pungent odor, and is less harmful to people, MDI has a low vapor pressure, is not easily volatilized, has no obtrusive stench, and has no specific transportation needs. There are stringent guidelines.

5. The manufacturing of firm foam, which is used in constructing energy-saving refrigerators,  freezers, etc., is the primary use of the downstream of polymerized MDI. About 35% of the polymerized MDI used worldwide comes from the construction industry, and 20% comes from refrigerators and freezers. Pure MDI makes up the majority of this usage. While the downstream of TDI is mostly employed in soft foam, it is also used to manufacture pulp, shoe bottoms, elastomers, etc. and is used in synthetic leather, shoemaking, vehicles, etc. The production of soft foam, which is used in furniture, vehicles, and other products, is thought to use around 80% of the total daily intake of TDI worldwide.

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