Difference Between MDI and TDI

The key difference between MDI and TDI is that MDI occurs as a light yellow crystalline solid, whereas TDI occurs as a clear, colourless to pale yellow colour liquid.

MDI and TDI are two different forms of diisocyanates. These are useful in polyurethane production. There are two major types of diisocyanates as aromatic diisocyanates and aliphatic diisocyanates. MDI and TDI are forms of aromatic diisocyanates.

CONTENTS

1. Overview and Key Difference
2. What is MDI 
3. What is TDI
4. Similarities Between MDI and TDI
5. Side by Side Comparison – MDI vs TDI in Tabular Form
5. Summary

What is MDI?

The term MDI stands for methylenediphenyl diisocyanate. It is useful for the production of polyurethane materials for many different applications, such as the manufacture of rigid polyurethane foams that are useful for home and refrigerator insulation. The insulation materials made with MDI helps the consumers in conserving energy.

On the other hand, there are some additional uses of MDI, including the production of coatings, adhesives, sealants, and elastomers. We can find this ingredient in products such as paints, glues, and weather-resistant materials. Moreover, this material is useful in making different types of footwear, sports and leisure products, and some specific flexible foams. In addition, we can use it as a binder for wood and in producing mould cores for the foundry industry.

When considering the composition of MDI, the basic chemical unit present in this material is 4,4’-diphenylmethane diisocyanate. Typically, it is a light yellow crystalline solid that does not occur naturally in the environment. Therefore, if this substance is released into the air, water and soil, it can cause health hazards such as respiratory effects.

What is TDI

The term TDI stands for toluene diisocyanate. It is useful in the production of polyurethane. TDI is used mainly for the production of flexible foam, including bedding and furniture, carpet underlayer, packaging applications, etc. TDI material is also important in the manufacture of coatings, sealants, adhesives, and elastomers. Similarly, TDI material is useful in transportation applications where it helps to make automobile parts lighter, leading to improvements in vehicle fuel efficiency and, therefore, energy conservation.

When considering the composition of TDI, the basic chemical unit present in this material is 2,4’-toluene diisocyanate. Typically, it is a clear, colourless to pale yellow colour liquid that does not occur naturally in the environment. Therefore, if this substance is released into the air, water and soil, it can cause health hazards such as respiratory effects.

What are the Similarities Between MDI and TDI?

• MDI and TDI are forms of aromatic diisocyanates.
• Both are aromatic compounds.

What is the Difference Between MDI and TDI?

MDI and TDI are two types of diisocyanates that do not occur in the environment naturally. MDI stands for methylenediphenyl diisocyanate, while TDI stands for toluene diisocyanate. The key difference between MDI and TDI is that MDI is a light yellow crystalline solid, whereas TDI is a clear, colourless to pale yellow colour liquid. When considering the toxicity of MDI and TDI, MDI has a low vapour pressure than TDI, which makes it less toxic as well. Thus, this is another difference between MDI and TDI. Moreover, MDI is mainly used for the production of rigid polyurethane foams, while TDI is mainly used for the production of flexible polyurethane foams.

The below infographic summarizes the differences between MDI and TDI in tabular form.

Summary – MDI vs TDI

MDI and TDI are two types of diisocyanates that do not occur in the environment naturally. The key difference between MDI and TDI is that MDI occurs as a light yellow crystalline solid, whereas TDI occurs as a clear, colourless to pale yellow colour liquid. More importantly, MDI is less toxic than TDI because MDI has a comparatively low vapour pressure.

Reference:

1. “Diisocyanates Explained.” Diisocyanates, Available here.

Image Courtesy:

1. “4,4′-methylene diphenyl diisocyanate” By Fvasconcellos 16:37, 6 October 2007 (UTC) – Own work (Public Domain) via Commons Wikimedia
2. “Toluene-2,4-diisocyanate-2D-skeletal” (Public Domain) via Commons Wikimedia