The Department of Chemical and Biological Engineering is pleased to present a seminar with department faculty member, John Torkelson.
"Upcycling Virgin and Waste Thermoplastic Polyethylene, Polypropylene, and Related Copolymers into Covalent Adaptable Networks that Recover Crosslink Density upon Recycling"
ABSTRACT: Approximately one trillion pounds of synthetic polymers/plastics are produced worldwide each year. However, less than 10% of spent polymers and plastics are effectively recycled. Polyethylene (PE) and polypropylene (PP) account for more than half of global polymer production; thus, approaches to address this recycling crisis should consider PE, PP, and their copolymers. We will describe how thermoplastic PE, PP, and associated copolymers, composed of linear or branched chains, can be upcycled into covalent adaptable networks (CANs) using a one-step, radical-based reactive processing method that is a simple “drop-in” modification of the commercial process used to make non-recyclable, permanently crosslinked PE (PEX) networks or thermosets from thermoplastic PE. The commercial process for making PEX thermosets, which have enhanced properties relative to thermoplastic PE and are produced at ~20 billion pounds annually, involves melt-processing PE with a low level of radical initiator, resulting in the transfer of a hydrogen atom from PE to the initiated radical. This transfer leaves a radical on the PE backbone that can react with another PE backbone radical, leading to a permanent crosslink. We developed dynamic covalent cross-linkers that can be “dropped into” the reactive process at several weight percent relative to PE or ethylene-based copolymer. This yields CANs with crosslinks that are robust under use conditions but dynamic during melt reprocessing, enabling recyclability. Our dynamic covalent crosslinkers yield PE CANs that recover the original crosslink density and properties after multiple recycling steps and exhibit markedly reduced elevated-temperature creep compared with thermoplastic PE. We will also show that direct free-radical copolymerization of ethylene with low levels of dynamic covalent crosslinkers can produce fully recyclable PE CANs. Our approach also enables us to overcome the challenge of forming networks by reactive melt-state processing of PP and propylene-based copolymers. No commercial crosslinked PP thermoset is produced by radical-based reactive processing because of chain scission. We overcame this problem by developing methods that stabilize radicals via resonance, yielding recyclable PP CANs that recover cross-link density upon recycling. Finally, we will discuss using CANs to mitigate the formation of microplastics.
John Torkelson is a Walter P. Murphy Professor in the Dept. of Chemical and Biological Engineering and the Dept. of Materials Science and Engineering at Northwestern University. He previously served as Associate Dean for Graduate Studies and Research in the Engineering School and Director of the Materials Research Center at Northwestern. He also held leadership roles in the Division of Polymer Physics of the American Physical Society and the Materials Engineering and Sciences Division of the American Institute of Chemical Engineers. John received the Tau Beta Pi Outstanding Teaching Award, the Lilly Foundation Teaching Award, the Northwestern University Alumni Association Excellence in Teaching Award, and both the McCormick School of Engineering Teacher of the Year Award and Advisor of the Year Award. In 2004, John’s research excellence was recognized with both the Wiley Polymer Physics Award and the Charles M. Stine Award from the Materials Division of AIChE. In 2025, he was named a “highly ranked scholar”by ScholarGPS in several categories based on lifetime achievement, including #1 in “Transition Temperature,” #1 in “Gradient Copolymer,” and #3 in “Glass Transition.” John was the 2026 Turner Alfrey Visiting Professor at Michigan State University-St. Andrews, and he and his research team were just named winners of the 2027 ACS PMSE Division Cooperative Research Award for the research he will discuss in his seminar at Northwestern University.
Cost: Free