Beckman Institute Postdoctoral Fellows Chai Saengow and Julian Cooper will present the Beckman Institute Director's Seminar at noon on Thursday, May 4 in 1005 Beckman and on Zoom. Lunch will be provided to in-person attendees.

Registration is required to attend.

"Leveraging chemistry to produce sustainable thermosetting materials on scale"

Julian CooperThermoset polymers are ubiquitous to our everyday lives. While prized for both their mechanical properties and chemical resistance, thermoset polymers lack effective recycling strategies. The same features that impart these crosslinked materials with desirable properties pose a direct challenge to their recycling and reclamation; consequently, most thermosets are discarded when they no longer meet performance needs. Approaches to tackle these limitations have sought to install specific chemical functionality into the thermoset that facilitates crosslink exchange, enabling the reprocessing and recycling of these materials when certain conditions are met. While these covalent adaptable networks represent an effective strategy for thermoset recycling and reclamation, the need for tailored functionality limits the scalability of this approach. Consequently, reprocessing of commodity thermosets remains a largely unmet challenge. Enabling reprocessability by leveraging functionality intrinsic to commodity materials would facilitate their reclamation and serve to circularize the thermoset lifecycle. This presentation will detail an unexpected but enabling approach to reprocess and regenerate thermosets using tools inherent to material manufacturing. By simply following where the science led us, we eliminate the need to install predesigned functionality to instill regenerative capabilities in a thermosetting material. We explore the parameters that influence reprocessability and find that conditions used to make the material greatly influence the chemistry that enables material reprocessing. We leverage this understanding to realize multigenerational capabilities in commodity materials, reclaiming properties across generations. The simplicity of the approach enables new end-of-life management strategies for a variety of readily scalable commodity thermosets and serves as an important advancement to realize a fully circular lifecycle for thermoset polymers.

Julian Cooper was born in Houston, Texas in 1992. He obtained his B.S. in chemistry from Rice University (not far from home!) in 2014. Following graduation, Julian pursued advanced studies in chemistry at the Massachusetts Institute of Technology as an NSF graduate fellow, where he completed a Ph.D. in chemistry with Profs. Jeffrey Van Humbeck and Alex Radosevich in late 2019. That same year, Julian joined Jeffrey Moore’s research group at the University of Illinois, where he is currently a Beckman postdoctoral fellow. His research leverages chemistry to address challenges in materials science. Outside of work, Julian enjoys reading, photography and playing golf.

"Imparting extensibility to jammed colloidal inks for direct-ink-writing printability"

Chai Saengow

We introduce and test the hypothesis that extensional rheology, as well as yield stress, are the two key rheological properties for jammed colloidal inks used in direct-write 3D printing of implantable lattice-structured bone scaffolds. Guided by prior observations that yield stress fluids can be engineered with high extensibility, and that higher extensibility of emulsion-based yield stress fluids enabled more robust printing, we describe an experimental study of these paste-like materials that varies ink formulation and flow conditions to map printability to these rheological properties. The inks consist of an aqueous suspension of hydroxyapatite particles (the main mineral of bone), irregularly shaped and sized 1-10μm, which creates a cementitious paste-like yield-stress fluid. To induce capillarity for better bone growth, we add sacrificial polymethyl methacrylate beads (PMMA, 5.96 ± 2.00μm in diameter) to create microporosity in the final scaffolds. This baseline formulation of ink is difficult to print due to brittle filament rupture if the nozzle speed is not closely matched to the average velocity of the extruded ink. We examine two methods to tune extensibility and yield stress: (i) incorporating polymer additives, and (ii) modulating electrostatic particle interaction. Hydroxypropyl methylcellulose serves as the polymer additive, tested at different loading. Polyacrylic acid and polyethylenimine coat the particles with negative and positive charge, respectively, to modulate yield stress. By mapping printability to the rheological design requirements of extensibility and yield stress, our results show how modulating these two key rheological properties can improve printability.

Chai Saengow is a Beckman Institute Postdoctoral Fellow. He is co-supervised by Prof. Amy Wagoner Johnson and Prof. Randy Ewoldt. He earned his Ph.D. from Queen’s University, Canada. His research targets modifying rheological properties of materials for 3D printing. Specifically, how to tune the two important properties simultaneously, i.e., extensibility and critical flow stress. Chai enjoys cooking, hiking, and spending time with his dog.