Manufacture of Biocompatible Catheter Tubes Sustainable polyurethane production without toxic isocyanate

Polyurethanes are found in many products, such as upholstered furniture, foam and insulation materials, flooring, paints, and even medical catheters. Toxic isocyanate is used in the production of these widely used plastics. Fraunhofer researchers have now developed an alternative production process using harmless dicarbamate.

Chemical compounds of the isocyanate type are toxic and can trigger allergies or asthma. However, they remain indispensable to the chemical industry: they are primarily needed for the production of polyurethanes (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 people and prevent health risks. 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 of the Fraunhofer Institute for Applied Polymer Research IAP and his team replaced isocyanate with the non-toxic dicarbamate. The new process makes the production of plastics easier and safer, and employees do not need special training to protect themselves from the toxic substance. Additional benefits: It results in lower greenhouse gas emissions, as the researchers use carbon dioxide to produce dicarbamate. They are also developing recycling methods to reuse spent PUR materials. 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 project “CO2NIPU.” Herfurth highlights the project’s advantages: “Polyurethanes made from dicarbamates have identical molecular structures to conventional PURs made from isocyanates. This means we can build on existing expertise to achieve the material properties required for the end product or application.”

Modular System for Material Properties

The researchers have further developed the process with a view to 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 impart elastic or adhesive properties. Polymer diols soften the plastic, while the dicarbamate—used as an isocyanate substitute—triggers the chemical reaction. After mixing, these chemicals are melted and stirred at temperatures between 180 and 190 degrees Celsius. After cooling, experts test for characteristics such as tensile strength and elasticity. Isocyanates are highly reactive, which is why polyurethanes often form within a few minutes. If less reactive dicarbamates are used, the same process takes six to eight hours, but the procedure is much easier to control and regulate. This reduces scrap and quality fluctuations in production.

Circular Economy for the Plastics Industry

Dicarbamates are produced by 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. As a first application, the Fraunhofer researchers have set their sights on the production of biocompatible catheter tubing for medical technology. Fraunhofer IFAM is using the variable modular system to develop adhesives for bonding cannulas to the tubing.

The technology for producing isocyanate-free polyurethanes is no longer limited to the laboratory. “We are now able to produce several kilograms of NIPU at our pilot plant. In the next step, several hundred kilograms of NIPU can then be produced at the Fraunhofer Pilot Plant Center for Polymer Synthesis and Processing (PAZ) in Schkopau,” says Herfurth.