Researchers at the Fraunhofer Institute for Applied Polymer Research IAPhave developed a foil that changes into polyurethane foam (PU foam) when heated– entirely without health risks.
The foil allows for isocyanate-free foaming, thus improving workplacesafety. Additionally, it offers logistics advantages for storage andtransportation. The material can be customized for various applications rangingfrom the automotive and construction industries to packaging.
“A frequently discussed aspect in the production of PU foam is the healthrisk at work from isocyanates, one of the main components in the chemicalreaction that forms polyurethane,” explains Dr. Thorsten Pretsch, head of theSynthesis and Polymer Technology research division at Fraunhofer IAP in thePotsdam Science Park. “Our foil enables isocyanate-free foaming. It minimizeshealth risks in the workplace and improves occupational safety, especially foron-site applications, such as in the construction industry,” emphasizes Dr.Pretsch.
Isocyanate-free foaming
Strict regulations and protective measures apply when handlingisocyanates. They are toxic and have a sensitizing effect on the respiratory tractand skin; some isocyanates are suspected of causing cancer.
The newly developed foil transforms into a PU foam simply by theapplication of heat, without undergoing any chemical reaction. The researchteam’s innovative approach also represents a new technology for foam productionitself: thermal foaming. The product is named FOIM – a combination of the words‘foil’ and ‘foam’.
Flexible: Polyurethane foam withshape memory
The novel material is a shape memory polymer. It is capable of returningto its original shape after being deformed. An external stimulus, such as heat,triggers the shape memory effect.
For the foil, the researchers synthesized a polyurethane foam and then compressedit. At a temperature of 60 degrees Celsius, the foil expands from 2.5 millimetresthick to a foam of 40 millimetres thickness – an expansion by a factor of 16.
The result is a soft-elastic PU foam with a density of 80 kilograms percubic meter. According to the DIN EN ISO 33861 standard, this is a low-densityfoam that is suitable for use as packaging material, among other things.
Space-saving: Semi-finished productsmade of shape-memory foam
Industrial production often uses polyurethane foams as standardized,prefabricated intermediate product in cut form. These so-called semi-finishedproducts are further processed or directly integrated into end products in themanufacturing process. They enable mass production while maintaining consistentquality.
Their drawback: polyurethane foams take up a lot of volume. “Our foilsaves space during transport and storage,” emphasizes Dr. Pretsch. “It is onlywhen heated to 60 degrees Celsius that the foil foams up. This benefits industrieslooking to reduce logistics costs and those where low transport volume isdesirable, such as the aerospace industry.”
Versatile: Insulating, backfilling,fixing with foil foam
Low-density PU foams are suitable for numerous fields of application andindustries: furniture manufacturers use them for upholstery; in the packagingindustry, they protect fragile goods during transportation; in the constructionindustry, PU foams backfill joints; and, in vehicle interiors, they are usedfor insulation or cladding.
Application tests for filling hollow cavity structures with the new foilwere successful. The material foamed almost completely when heated, even incomplex geometric shapes.
The foil is also suitable for use in bonding and joining technology. Theresearchers demonstrated that two objects can be fixed in place by foaming acavity between them.
The properties of the innovative material are variable: the researchscientists can individually adjust the flexibility and transparency of the foilbefore foaming. The same applies to the density, thermal conductivity,elasticity, and compression properties of the foam.
“We adapt the properties of the material to the technical requirements ofdifferent applications. From car interiors to medical treatments and theprotection of fragile goods,” concludes Dr. Pretsch.