Polyolefin Upcycling Through Dehydrogenation & Functionalization
Karen I. Winey, University of Pennsylvania (PI)
Ryan Coughlin, University of Massachusetts, Amherst
Karen I. Goldberg, University of Pennsylvania
Raymond Gorte, University of Pennsylvania
Marisa Kozlowski, University of Pennsylvania
Daeyeon Lee, University of Pennsylvania
John Vohs, University of Pennsylvania
Plastics are inseparable from modern life. Moreover, their light weight, chemical and mechanical durability, selective permeability, and design flexibility allow plastics to mitigate some of the world’s most pressing challenges including reducing food spoilage, preventing the spread of infectious disease, and reducing energy consumption. But the benefits of plastics also come at a cost. Their production, particularly polyethylenes and polypropylenes which are the focus of this work, consumes energy and non-renewable natural resources. After use in the USA, they are overwhelming disposed of in landfills. Our proposed research aims to convert discarded polyethylenes and polypropylenes into specialty polymers via chemical upcycling.
Post-consumer polyolefins (various polyethylenes and polypropylenes) cost ~ $0.20 – $1 per pound, while specialty polyethylene copolymers synthesized by traditional means sell for ~ $5 – $10 per pound and have improved toughness and adhesive properties. To transform specialty polyolefin production from relying on traditional feedstocks to using waste polyolefins as a new, greener feedstock is a significant chemical challenge, because polyolefins have exceptional chemical and thermal stability. Thus, our proposed work endeavors to master the chemical mechanisms of (1) polyolefin dehydrogenation (converts carbon-carbon single bonds to double bonds) and (2) chemical functionalization to convert polyolefins into copolymers. Note that commercially successful polyethylene copolymers are often synthesized with just 1 – 10 mol% of the functional comonomer, indicating that only 0.5 – 5% of the backbone carbon atoms in the waste polyethylene need to be converted to produce more sustainable specialty polyolefins. In addition, several of the new chemical transformations investigated will produce new polymers, for example sulfonated polyethylenes and functionalized polypropylenes.
Our innovative approach to transforming polyolefin waste into functionalized polyolefins has two key attributes. First, polymer molecular weight will be maintained or increased through the transformations by avoiding reactions that induce chain scission. This approach is significantly more energy efficient thanreducing a polymer to monomers, purifying the monomers, and then repolymerizing. Second, we are targeting energy-efficient and environmentally-friendly reactions, so that our foundational work can be readily transformed to practice. While our primary effort will focus on a two-step chemical route, we will also investigate one-step chemical routes to simultaneously dehydrogenate and functionalize polyolefins for additional gains in energy efficiency. Our synthetic efforts will be complimented by extensive polymer property measurements and benchmarking against commercial polymers. Our distinctive strategy for converting waste polyolefins into higher-value functionalized polyolefins is applicable to both single- and mixed-stream polyolefin waste.
Our approach to converting waste commodity polymers into specialty polymers is a viable and valuable step toward a comprehensive effort to reduce polymer waste. Moreover, we anticipate that our foundational work will expand the conversion of waste plastics as a feedstock in the production of an ever-increasing range of high-value plastics.