Description:

The Program on Plastics, Ecosystems, and Public Health (PEPH) is delighted to host a series of exclusive discussions on challenges associated with the global use and accumulation of plastic. Space is limited!

Lunch provided for in-person attendees. Registration is required.

TITLE: "New Methods for Sustainable Recycling and Upcycling of Traditionally Non-Recyclable Polymers: Transforming Thermosets into Reprocessable Thermoplastics Using Dynamic Covalent Bonds"

WHEN: Wednesday May 3, 12 – 1 pm CDT 

FORMAT: Hybrid event (in-person and virtual)

WHERE: For in-person attendees, Ford Motor Company Engineering Design Center, Room 2.350; Zoom for virtual attendees (webinar link provided ahead of the event)

SPEAKER: John M. Torkelson, Walter P. Murphy Professor of Chemical and Biological Engineering and Materials Science and Engineering at Northwestern University

ABSTRACT: Thermosets or conventionally crosslinked polymers, e.g., rubber tires and foam mattresses, cannot be melt-reprocessed because the permanent crosslinks prevent melt flow. The inability to undergo melt flow prevents effective high-value recycling of thermosets, leading to major sustainability and economic losses because thermosets constitute as much as 20% of the 800 billion pounds of polymers produced annually worldwide. We shall describe several new, one-step methods for making crosslinked polymers with covalent crosslinks that are robust at use conditions but dynamic at high temperature, thus facilitating melt-reprocessing and recycling. Crosslinked polymers or polymer networks are synthesized by two classes of reactions: addition and step-growth. The Torkelson group has developed dynamic covalent polymer networks for both reaction classes. Regarding addition-type networks produced using free-radical chemistry, we have developed simple dynamic covalent crosslinkers that can be added at low levels, e.g., 5 mol%, to reactions that otherwise would lead to linear polymers. With the dynamic crosslinker covalently incorporated, the networks can be reprocessed multiple times with full recovery of crosslink density and associated properties and exhibit resistance to creep a few tens of degrees below the reprocessing temperature. Importantly, this same dynamic covalent crosslinker can be used to upcycle waste polyethylene (the most common plastic in the recycle stream) into more valuable crosslinked polyethylene (PEX) that in turn can be reprocessed multiple times with full property recovery. Regarding step-growth type networks, we have taken on the challenge of polyurethane networks which exhibit poor reprocessability and are made from toxic isocyanates. We have developed two types of non-isocyanate polyurethane, one based on polyhydroxyurethane and another on non-isocyanate polythiourethanes, that exhibit reprocessability with full crosslink density and property recovery and can be made from biowaste compounds, adding further sustainability and economic benefits. With polyhydroxyurethane networks, we have developed foams that could replace polyurethane foams that constitute the majority of polyurethane production.   

Questions? Contact mike.mcmahon@northwestern.edu