We have successfully produced soybean oil-based recyclable polyurethane foams (SO-PUFs) with high commercial soybean oil polyol contents. Soy polyols can substitute up to 50% of the petrochemical polyols (approximately 30% of total mass of the foam) in the new products. The foaming method and operation conditions for the recyclable SO-PUF are basically the same as that of conventional PUFs. The major difference is that dibutyltin dilaurate (DBTDL), an inexpensive compound, in an amount of up to 0.5 wt% of overall PUF mass, is used as the catalyst instead of tertiary amines used in conventional PU foaming. It is exciting to note that partial substitution of petrochemical polyol with soy polyol resulted in significant increases in elastic modulus and tensile strength and retained the tear strength. The elongation at break exhibited slight (~5%) to moderate (~31%) decreases, depending on the content and grade of soy polyols used. The compression stress of the SO-PUF is also significantly higher than its petrochemical counterpart. On the other hand, the wet compression set of SO-PUF increased 10 to 33% depending on the composition. These results suggest that the SO-PUF with proper composition is likely to replace petrochemical PUF in some applications. The differences between the SO-PUF and the petrochemical PUF (control) are due to their difference in hydroxyl value of the polyol. Soybean oil polyols generally have much higher hydroxyl values than those petrochemical polyols used for PUFs, resulting in foams with higher firmness and compression set. The SO-PUFs demonstrated facile recyclability through compression molding, and the solid PU plastics exhibited decent mechanical properties. However, recycling through compression molding is a slow process and is subject to thermal degradation. With what we have learned and achieved, we are ready to move forward with the investigation to the next phase of research: (1) introducing a small amount of disulfide chemicals in the networks of SO-PUFs for faster bond exchanges and hence faster recycling rate; (2) to recycle the SO-PUFs in a rapid manner (prevent degradation) via extrusion compounding with other thermoplastic waste; (3) improving soy polyol with more precise functionality and molecular weight.

Inclusion of 30% soy polyol in polyurethane foam that displays comparable performance to conventional petrochemical polyurethane is a great milestone in pursing use of soy polyol for foam product. Specifically, this new soy-based foam product is recyclable, a unique property not attainable to the conventional foams. As government, industry and public have all reached a consensus that there is an urgent need to drastically reduce plastic waste in rivers, oceans and landfills and secure the long-term sustainability of plastic materials, it is a right time for us to develop next-generation SO-PUF with designed recyclability. The technology developed from this project will make the SO-based foam products more competitive and attractive by closing the loop in material circularity which would allow U.S. soybean farmers and related industry to play a larger role in the transition to circular economy for plastics.