Isocyanate-Free Polyurethane (NIPU) Produced Using CO2 as a Raw Material
Isocyanates and other chemicals are toxic and can trigger allergies or asthma. However, they remain indispensable in the chemical industry, especially in polyurethane production. Polyurethane materials have a wide range of applications, making them essential in many products. While the final product no longer contains isocyanates, special safety precautions must be taken during production to prevent harm to workers. Currently, the CO2NIPU project at Fraunhofer Research (IAP) has successfully produced isocyanate-free polyurethane (NIPU) for the first time.
Substitution of Isocyanates with Carbamates
To achieve this, Christoph Herfurth, the project leader of the Fraunhofer Institute for Applied Polymer Research (IAP), and his team replaced isocyanates with the harmless carbamates. This innovative process makes polyurethane production safer and more convenient. Workers no longer need specialized training to protect themselves from this toxic substance. Moreover, this process helps reduce greenhouse gas emissions. Researchers are using carbon dioxide to produce carbamates and are also developing recycling techniques for waste polyurethane materials.
In addition to Fraunhofer IAP, the CO2NIPU project also involves Fraunhofer Institute for Chemical Technology (ICT), Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM), and Fraunhofer UMSICHT Institute for Environmental, Safety, and Energy Technology.
Christoph Herfurth highlighted the advantages of this innovative project: "The molecular structure of polyurethane made from carbamates is identical to that of conventional polyurethane made from isocyanates. This means we can use existing expertise to achieve the material properties required for the final product or application."
Modular Control of Material Properties
The research team further improved the process for industrial applications. By precisely adjusting the ratio of different chemicals, they were able to control the desired characteristics: chain extenders promote molecular crosslinking to adjust elasticity and viscosity, polymer diols act as plasticizers to soften the material, while carbamates, replacing isocyanates, serve as the reaction initiators. These raw materials are mixed and melted at high temperatures of 180-190°C, and after cooling, key indicators such as tensile strength and elasticity are tested.
Compared to highly reactive isocyanates that complete polyurethane synthesis in minutes, the low reactivity of carbamates extends the reaction to 6-8 hours. However, this greatly enhances process control and effectively reduces production waste and quality fluctuations.
Building a Circular Economy in the Plastics Industry
The carbamates are produced using a high-pressure process developed by Fraunhofer UMSICHT Institute. Methanol and carbon dioxide react with diamines at a pressure of 50 bar to synthesize carbamates. Fraunhofer ICT has developed a recycling process for waste polyurethane (such as from old foam materials), which is then reprocessed to produce new polyurethane products.
Christoph Herfurth concluded: "Thus, we are contributing to the achievement of the sustainable circular economy goal with zero greenhouse gas emissions."
Currently, the research team has targeted the medical field, with bio-compatible catheters as the first application. Fraunhofer IFAM is using a variable modular system to develop specialized adhesives for bonding needles and catheters.
This isocyanate-free polyurethane production technology has now moved beyond the laboratory stage. Christoph Herfurth revealed, "Pilot-scale production of NIPU has been achieved at the kilogram level, and the next step is to scale up to hundreds of kilograms at the Fraunhofer Polymer Synthesis and Processing Pilot Center."