Vitrimers from Unentangled Polypropylene

Polypropylene (PP) is extremely ubiquitous and widely used in numerous applications, such as single-use plastic bags, food packaging, automotive, and medical supplies. For single-stream PP waste, mechanical recycling allows their reuse into new products. However, after multiple reprocessing events PP often exhibits very low viscosity and brittle mechanical properties, as a result of a large number of chain scission events. The recycled use of low molecular weight PP waste toward circular economy is a great challenge. This talk will discuss the ability to upcycle these water materials to vitrimers, allowing their further use with significantly improved thermal and mechanical properties. We will focus PP resins that contain maleic anhydride (MA) functional groups, which can be dynamically crosslinked with epoxide-functionalized polyethylene glycol (PEG) molecules through epoxy-anhydride curing chemistry with the presence of Zn-based catalyst. The impact of crosslinker chemistry and molecular weight on the resulting vitrimer properties will be discussed, including degree of crystallinity, crosslinking density, and mechanical performance. Building upon these results, we further investigate the use of vitrimers from low-molecular weight PP as post-consumable recyclates (PCR), blended with virgin PP plastics for product manufacturing, following state legislatures which mandate PCR content.