Tunable Functionalization and Upcycling of Polyolefins to Polyurethanes

By 2050 the accumulation of plastic waste is projected to reach 12,000 Mt, where 18% are recycled, 24% incinerated, and the remaining 58% are either landfilled or enters the natural environment (In the US, only 9% is recycled). The main contributors to this waste are polyolefins, which constitute roughly 45% of all plastic waste (76% at the U.S. level). Momentum has shifted towards looking for a solution for polyolefin waste and moving to a circular economy. Post-polymerization modification has shown promising results to upcycle polyolefins, removing the limitation of inertness, and improving the final physical properties of the material. Subsequently, this modified polyolefin can be repurposed in a wide variety of applications including polyurethanes, foams, coatings, and films, among others. In this work, polypropylene (PP) was functionalized and upcycled to polyurethanes. First, hydroxylated PP (PPOH) was synthesized through the hydroxylation of maleic anhydride-grafted PP. Then, the polyurethane (PU) was synthesized by the reaction of PPOH with a diisocyanate in solution and in the melt. Melt processing was enabled by using a blocked isocyanate that delayed the crosslinking reaction for easy processability. The presence of PU crosslinks and PP strands in the network were confirmed with spectroscopy. At a low level of maleation and hydroxylation, the PP thermal properties (glass transition, melting, and crystallization temperatures) were unaffected by functionalization, PP crystallization was still observed in the PU network that contained PP segments.