McKenzie Coughlin (she/her) is a postdoctoral researcher in the Polymer Processing group with a background in polymer physics. Her research at NIST looks at the rheology and crystallization of mixed polyolefins with the goal of improving the properties of recycled polymer blends. McKenzie earned a B.S. in chemical engineering from the University of Florida in 2016. She earned a Ph.D. in chemical engineering from the University of Minnesota in 2021, studying the effects of architecture on the properties of graft copolymers both in the melt and in solution. She joined NIST in 2021 as a guest researcher through Georgetown University, before starting as an NRC postdoc in 2023.
Plastics are ubiquitous in today’s commercial materials, and polyolefins, such as polyethylene (PE) and polypropylene (PP), are commonly used in packaging and make a large portion of the waste stream. However, recycling rates of these materials remains low, leaving most to head for landfills and creating significant environmental concerns. In mechanical recycling, PE and PP enter the waste stream mixed and form micro-separated domains when melted together. The blends crystallize in a cascading fashion when cooled, resulting in brittle materials with poor mechanical properties.
McKenzie’s work focuses on developing a fundamental understanding of the crystallization process in polyolefin blends, particularly under shear conditions. By examining how blend composition, shear rate, and the addition of compatibilizers affects the rheology and crystallization kinetics, we can better understand how to improve the strength of recycled plastics and overall mechanical properties. McKenzie employs the NIST rheo-Raman microscope, polarized optical microscopy, and small-angle X-ray scattering to study the crystallization in these blends during cooling.