MESD Poster Award Introductions

Increasing demand for high performance plastics and elastomers and the associated environmental issues present society with enormous engineering challenges.¹ In this poster, I will highlight my postdoctoral work on promoting the sustainability of polymers, under the guidance by Prof. Bates and Prof. Ellison at University of Minnesota and in collaboration with many other researchers in the Center for Sustainable Polymers. The projects will be discussed in this poster can be summarized as follows:

Reversibly Cross-Linked Nonwoven Fibers: Sustainability Meets Melt Blowing

Melt blowing is a 60-year-old polymer processing method for producing nonwoven polymer fibers. It combines polymer melt extrusion with high-velocity hot air jet fiber drawing to produce nonwoven fibers in a single step. Due to its simplicity and high-throughput nature, melt blowing produces more than 10% of the $50 billion global nonwovens market. Semi-crystalline thermoplastic feedstocks, such as poly(butylene terephthalate) and polypropylene, dominate the melt blowing industry due to facile melt processability and product thermal/chemical resistance; other amorphous commodity thermoplastics (e.g., (meth)acrylates) are generally not employed because they lack one or both attributes. Cross-linking nonwoven products could enable more demanding applications, but cross-linking must be implemented after fiber formation. This poster describes melt blowing linear acrylic polymers containing cross-linkable functional groups, which were activated via either a cooling-induced Diels-Alder reaction² (e.g., furan-maleimide reaction) or a light-induced cycloaddition reaction³ (e.g., anthracene photodimerization). The resulting fibers possessed nearly 100% gel content and exhibited enhanced thermomechanical properties with higher upper service temperatures (e.g., ∼180 °C for anthracene-dimer cross-linked acrylic fibers) relative to the linear precursors. Due to the dynamic nature of the reversible cross-links at elevated temperatures, these cross-linked fibers can be recycled after use, providing new approaches to producing sustainable nonwoven products.

Reprocessable Thermoset Photopolymers: Sustainability Meets Three-Dimensional (3D) Printing

Three-dimensional (3D) printing, also referred to as additive manufacturing, has been globally recognized as a revolutionary technology which enables manufacturing materials with complex architectures that are often challenging to achieve using conventional methods. Among the existing 3D printing techniques, vat photopolymerization (e.g., stereolithography) offers superior feature resolution and contributes to nearly half of the 3D printing market. In a typical vat photopolymerization process, a liquid, reactive precursor mixture (usually comprised of acrylic monomers/oligomers, one of which being multifunctional and acting as a cross-linker) is selectively cured by a light-activated polymerization, resulting in permanently cross-linked photopolymers with robust mechanical properties and superior chemical/thermal resistance. These very characteristics that make them attractive also prohibits them from being reprocessed and thus recycled after use. Therefore, conventional 3D printed photopolymers are generally disposed as waste at the end of their product life, leading to issues ranging from economic loss to environment problems. Herein, dynamic covalent chemistries (e.g., thermoreversible Diels-Alder chemistry) were employed in vat photopolymerization to impart repairability and recyclability into 3D printed structures. The printed materials possessed nearly 100% gel content (indicative of network structures) and exhibited tailorable thermomechanical properties. Additionally, the dynamic linkages present in the network could enable effective reprocessing and reuse of these reversibly cross-linked photopolymers. For example, they could be reused as feed materials for extrusion-based processing techniques, such as fused deposition modeling (a type of 3D printing) and melt blowing (for cross-linked nonwoven production). Overall, this study demonstrates a promising route to recyclable thermoset photopolymers, providing sustainability to 3D printed materials and potentially advancing other applications such as self-healable coatings and adhesives.

References

1. Xu and Jin et al., Macromolecules 2018, 51 (21), 8585-8596.
2. Jin et al., ACS Macro Lett. 2018, 7 (11), 1339-1345.
3. Jin et al., ACS Appl. Mater. Interfaces 2019, 11 (13), 12863-12870.

Research Interests:

Following my passion for the science and technology of polymeric materials and my commitment to a sustainable future, I am pursuing a tenure track faculty position. As a faculty member, I plan to establish an interdisciplinary research group dedicated to both fundamental and applied aspects of materials and technologies that can help address pressing global issues in energy, environment, and sustainability. More specifically, I aim to develop hierarchical polymeric materials (e.g., block polymers for photovoltaics, polymer nanocomposites for all-solid-state batteries, and covalent organic frameworks as porous membranes and absorbents) that can facilitate the development of efficient renewable energy harvesting processes and high-capacity energy storage systems as well as addressing environmental challenges, including air and water purification. As a chemical engineer who is equipped with synthetic chemistry skills and advanced characterization techniques, I will design hierarchical polymeric materials at a molecular level, direct assembly at a microscopic scale, and thereby control macroscopic material properties and performance.

Teaching Interests:

During my Ph.D. studies, I had the opportunity to teach ~30%, 10 lectures in total, of an undergraduate/graduate level course (Introduction to Polymers), which helped me develop the skills of a lecturer and instructor (e.g., designing exams/homework sets, holding office hours, and grading exams). Outside of the classroom, I have directly advised 7 students (including undergraduate, master, and first-year Ph.D. students) in total, through which I have honed my mentorship skills and enhanced my inter-personal skills. These experiences have sculpted my teaching and mentoring philosophy, central to which are three main concepts: know the audience, teach fundamental knowledge with problem-solving skills, and learn through teaching. My interdisciplinary background would allow me to teach many undergraduate/graduate classes, especially those in a standard chemical engineering curriculum (e.g., reaction kinetics and transport phenomena). As a polymer scientist, I am enthusiastic to teach topical courses in polymer science, including polymer chemistry, polymer physics, rheology, polymer engineering/processing, and soft materials characterization. Additionally, I am always willing to teach other subjects that might be outside my area of expertise as I believe that the best way to learn is to teach. Throughout the course, I will integrate current research challenges and build discussion points into lectures to engage students by having them use their fundamental knowledge to analyze and solve real-world problems. I believe this can help develop their critical thinking and problem-solving skills which are key to their success as the next generation of well-rounded scientists.