MSE Seminar: “Compatibilizer Design for Mechanical Recycling of Polyolefin-containing Mixed Plastic Waste”

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Abstract

Mechanical recycling of plastics involves sorting, grinding, washing, and melt reprocessing waste into a new form. A major challenge is imperfect sorting, which leads to impure recyclate streams that phase separate as immiscible polymer blends when melt reprocessed. The final product is brittle because of the sharp polymer-polymer domain interfaces that are mechanically weak. This deficiency can be overcome by copolymer compatibilizers that localize at blend component interfaces and mechanically anchor into each domain, producing tougher blends.

In this talk, I will describe two examples of compatibilizers we developed for producing tough polyethylene terephthalate (PET)/polyethylene (PE) blends, a common pair of polymers found in packaging. The synthesis of PET-PE multiblock copolymer compatibilizers and their use as both adhesive layers in-between PET/PE multilayer films and additives for recycling PET and PE mixed waste streams will be described.

A different approach will also be highlighted involving hydroxy-functional polyethylene reactive compatibilizers. It is hypothesized that the compatibilization efficacy of these additives originates from catalyst-free transesterification reactions with PET during melt mixing to form predominantly PET-PE-PET triblock copolymers. The data suggests that the formed triblock copolymer compatibilizers form topologically trapped entanglements of the PE mid-blocks with nearby LLDPE homopolymer chains by a hook-and-clasp mechanism.

Importantly, both approaches have been shown to be remarkably efficient, compatibilizing blends at loadings as low as 0.5 wt%.

Bio

Chris Ellison, Ph.D.

Professor, Chair, Department of Chemical Engineering and Materials Science
University of Minnesota

Dr. Chris Ellison is a professor and the Lanny and Charlotte Schmidt Endowed Chair in the Department of Chemical Engineering and Materials Science at the University of Minnesota (UMN). He is also the director of the Industrial Partnership for Research in Interfacial and Materials Engineering (IPRIME), which connects companies from all over the world with academic researchers at UMN who are pursuing leading fundamental research.

He has a B.S. in Chemical Engineering from Iowa State University and received his Ph.D. in Chemical Engineering from Northwestern University. He started his faculty career at the University of Texas at Austin in the McKetta Department of Chemical Engineering in 2008 and then relocated to UMN in 2016. His research group focuses on polymer science and engineering, with an emphasis on the intersection of polymer physics, processing, and sustainability.