BMS and partners develop PU nanofoams for insulation

The thermal insulation performance of a PU rigid foam mainly depends upon the size of the foam pores. The smaller the diameter, the lower the thermal conductivity and the better the insulating effect. Today's PU rigid foams typically have pore sizes of roughly 150 µm, which exceeds the pore size of nanofoams planned for the future by a factor of approximately 1,000. Partnering with Prof. Reinhard Strey, University of Cologne's Institute of Physical Chemistry, for this project, BMS is focusing efforts on microemulsions, which react under supercritical conditions to form PU rigid foams with pore sizes of less than 150 nm in diameter. This type of material has the potential to double the thermal insulation performance of today’s PU rigid foams, thereby significantly increasing the energy efficiency and available internal space of refrigerators.

To synthesise a nanofoam under supercritical conditions, CO₂ and the liquid PU raw materials are mixed with the help of special surfactants at a pressure of 200 bar to form a microemulsion consisting of nanometre-sized droplets filled with CO₂ and encapsulated in surfactants. The pressure is then reduced, causing the CO₂ to expand and the droplets to become bubbles still in the nanometre range. At the same time, the PU raw materials react to form a three-dimensional polymer network that is a rigid PU foam. The most difficult challenge is to optimally coordinate the reaction of the PU raw materials with the expansion of the CO₂ bubbles to create nanopores of the desired diameter. Due to the severity of the challenge it is expected to take several more years to perfect the process.