Upcycling Postconsumer Polypropylene into High-Melting-Point Wax via Thermal Degradation

Abstract

The recycling rate of polypropylene (PP) lags behind that of poly(ethylene terephthalate) and polyethylene due to logistical challenges related to collection, sorting, and transportation to larger central processing centers and the lack of a stable end market. Conversion of polypropylene to a high-melting-point wax can reduce transportation costs through densification. It can also facilitate market diversification. We demonstrate the successful conversion of four PP feedstocks to wax in an autoclave at a temperature of 250 °C and pressure <5 atm. The resulting waxes exhibited molecular weights, melting points, crystallinity, and viscosities comparable to commercial PP wax. Wax color, while light, was darker than commercial wax and was improved by hydrogenation. These findings support the viability of decentralized PP recycling and create new opportunities for postconsumer PP valorization.