Healthier Reaction Polyurethane Can Do Without Isocyanate!

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Fraunhofer-Institut für angewandte Polymerforschung

Wuxi InfiMotion Technology Co., Ltd.

Polyurethane (PUR) is an important plastic. It is used to make paints, foams, hoses, shoe soles and much more. But one of its raw materials is toxic. This could soon change ...

Polyurethanes (PUR, or just PU for short) are produced from polyols—polyhydroxide compounds that are also found in chewing gum—and the relatively toxic isocyanates by means of a polyaddition reaction. Although the finished PUR is no longer toxic, those involved in its production are exposed to the substance. Therefore, some effort must be made to ensure that nothing can happen. Researchers from the Fraunhofer Institute for Applied Polymer Research (IAP) in Potsdam, Germany have therefore considered whether it might be possible to do without isocyanate. As it turned out, polyaddition with polyols also works with the harmless dicarbamate. The work was carried out as part of the "CO2NIPU" (Non-Isocyanate Polyurethanes = NIPU) project.

Isocyanate Replacement Without Property Changes

The Potsdam (Germany) team replaced the questionable isocyanate with harmless dicarbamate. The procedure, described as innovative, not only makes the production of PUR plastics safer but also simpler, as employees do not need to be specially trained to protect themselves from the toxic isocyanate. The experts use carbon dioxide (i.e. CO₂) for the production of dicarbamate. They are also developing suitable recycling methods to reuse used PUR materials. According to the researchers, polyurethanes produced with dicarbamates have identical molecular structures to classic PUR. It would therefore be possible to build on existing manufacturing expertise to achieve the exact material properties required for the end product or application. Polyurethanes are extremely versatile. They can be made as soft as butter or as hard as a bone. They can also be used to produce foams of different densities. They are also known as good adhesive systems.

How Non-Toxic Polyurethanes Are Made

The IAP researchers have already developed the process further in the direction of industrial feasibility, as they say. Different chemicals are mixed in a specific ratio. This is how the desired properties of the finished plastic part are created. So-called chain extenders help to cross-link the molecular groups of the starting materials. They also ensure elasticity or more sticky properties. The polyols make the plastic soft, the dicarbamate (as an isocyanate substitute) sets the rather exothermic reaction process in motion. After cooling, tensile strength or elasticity is tested. However, it must be said that dicarbamate reacts much more slowly than isocyanate. However, the reaction is easier to monitor and control and it is possible to reduce rejects and better counteract quality fluctuations. It is already possible to produce on a pilot plant scale. The researchers are talking about several pounds of NIPU.