Chemical compounds of the isocyanate type are toxic and can trigger allergies or asthma. Nevertheless, they remain indispensable to the chemical industry: they are primarily required for the production of PUR. These plastics are extremely versatile and are therefore used in numerous products. Although the final product no longer contains isocyanates, special safety precautions are required during production to keep them away from humans and avoid health hazards. In the “CO2NIPU” (Non-Isocyanate Polyurethanes, NIPU) project, Fraunhofer researchers have now succeeded for the first time in producing polyurethanes without the use of isocyanates.

Dicarbamate as a substitute for isocyanate

To achieve this, project leader Dr. Christoph Herfurth from the Fraunhofer Institute for Applied Polymer Research IAP and his team replaced isocyanate with the harmless dicarbamate. The innovative process makes the production of plastics simpler and safer, and employees do not need special training to protect themselves from the toxic substance. Further advantages: fewer greenhouse gas emissions are generated. This is because the researchers use carbon dioxide for the production of dicarbamate. In addition, they are developing recycling methods to reuse spent PUR materials.

Identical molecular structures

In addition to the Fraunhofer IAP, the Fraunhofer Institute for Chemical Technologies ICT, the Fraunhofer Institute for Manufacturing Technology and Applied Materials Research IFAM, and the Fraunhofer Institute for Environmental, Safety, and Energy Technology UMSICHT were also involved in the joint CO2NIPU project. Herfurth highlights the advantages of the innovative project: “Polyurethanes made from dicarbamates have identical molecular structures to classic PUR made from isocyanates. This allows us to build on existing expertise to achieve the material properties desired for the end product or application.”

Modular system for material properties

The researchers have further developed the process toward industrial feasibility. Different chemicals are mixed in specific ratios to produce the desired properties. So-called chain extenders help cross-link the molecular groups and provide elastic or adhesive properties. Polymer diols soften the plastic, while the dicarbamate—used as an isocyanate substitute—initiates the chemical process. After mixing, these chemicals are melted and stirred at temperatures between 180 and 190 degrees Celsius. Once cooled, the experts test for characteristics such as tensile strength or elasticity.

Less waste and fewer quality fluctuations

Isocyanates are highly reactive, which is why polyurethanes often form within minutes. When less reactive dicarbamates are used, the same process takes six to eight hours, but the procedure is much easier to monitor and control. This reduces waste and quality fluctuations in production.

Circular Economy for the Plastics Industry

Dicarbamates are produced at project partner Fraunhofer UMSICHT using a high-pressure process. At a pressure of 50 bar, methanol and the greenhouse gas CO2 are synthesized with diamines to form dicarbamates. Fraunhofer ICT is developing recycling processes for used polyurethanes, such as those from old foams, which are then reprocessed into new PUR products. “In this way, we are contributing to the goal of a sustainable circular economy without greenhouse gas emissions,” Herfurth summarizes.

First Applications

As a first application, the Fraunhofer researchers have set their sights on the production of biocompatible catheter tubing in medical technology. Fraunhofer IFAM uses the variable modular system to develop adhesives for bonding cannulas to the tubing.

NIPU from Schkopau

The technology for producing isocyanate-free polyurethanes now works beyond the laboratory. “We are already able to produce several kilograms of NIPU in our pilot plant. In the next step, several hundred kilograms of NIPU can then be manufactured at the Fraunhofer Pilot Plant Center for Polymer Synthesis and Processing (PAZ) in Schkopau,” says Herfurth.

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