Evanston, Illinois – Scientists at Northwestern University, working in collaboration with BASF, have developed a way of recycling polyurethane foam into new foams. The regenerated foam retains the durability of the original, along with its structural and chemical integrity.
Earlier attempts to recycle thermoset PU foams involved using carbamate exchange catalysts to convert them into covalent adaptable networks (CANs) that can be reprocessed at higher temperatures, but this creates films which are not as useful. The Northwestern team looked at the simultaneous reprocessing and refoaming of thermoset PU foams instead. To do this, they took advantage of the fact that the PU CANs can be melt processed. Cell growth was achieved by gas generation within a twin-screw extruder.
The refoaming process uses a zirconium-based catalyst, which is less toxic than more traditional tin-based PU foaming catalysts such as dibutyltin dilaurate. Both Zr(acac)4 and Zr(tmhd)4 proved effective, and could reprocess the foam successfully four or five times.
They found the foam-to-foam extrusion process gave controllable, continuous and uniform foam structures. The team suggest that the strategy could allow a range of different thermoset PU foams could be recycled in this way. The process has the potential for scalability, and could be applicable to both industrial scrap and post-consumer waste. Patents have been applied for.
The work has been published in the journal Advanced Materials, and the development of the catalyst in Macromolecules.
