NU 2020-045
INVENTOR John Torkelson*
SHORT DESCRIPTION A method to recycle and depolymerize polymer network substitutes for traditional cross-linked polymers
BACKGROUND Polyurethanes (PUs) are among one of the most widely used polymers worldwide, with 2020 annual production estimated to be ~29 billion kg. The applications of PUs include elastomers, adhesives, coatings and foams, and roughly 85% of PU production associated with cross-linked architectures or networks. Despite their high economic value, traditional cross-linked polyurethane network materials cannot be efficiently recycled, leading to major economic and sustainability losses. In traditional cross-linked PUs, permanent covalent bonds prevent them from being reprocessed in the melt state, leading to major sustainability and economic losses. Current studies on recyclable polyurethane networks have not achieve full recovery of both cross-link density and tensile properties after reprocessing.
ABSTRACT Northwestern researchers have discovered a well-designed dynamic polyurethane network with full property recovery after multiple reprocessing steps. The method enables nearly 100% recovery of dynamic covalent PU networks with cross-link density and tensile properties after multiple reprocessing steps. By incorporating a small excess of free hydroxyl groups and/or increasing the cross-linker functionality, the property recovery and thermal stability of dynamic covalent PU networks may be significantly enhanced. While free hydroxyl groups suppress the reversion of urethane links and minimize side reactions associated with liberated isocyanate groups under reprocessing conditions, tetrafunctional cross-linkers help to maintain network integrity in the presence of small levels of side reactions. In addition to melt-state reprocessing, this material also has the potential to be recycled through monomer recovery. They demonstrate this potential by alcoholysis under relatively mild conditions. The novel work developed at Northwestern not only offers a solution to the long-standing issue of PU network recycling, but also provides simple strategies to improve property recovery of reprocessable networks. As a result, the economic value of highly-engineered polyurethane products can be at least partially reclaimed at their end of use. Additionally, the efficient recycling strategy minimizes the environmental impact resulted from spent, waste polyurethane materials.
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ADVANTAGES
IP STATUS A US patent application has been filed.