CAREER: Multiscale Mechanics of Bio-based, Reprocessable, Recyclable and Mechanically Robust Polymer Composites

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This Faculty Early Career Development (CAREER) grant will support fundamental research to understand complex mechanical behaviors of bio-crosslinked polymer composites. Covalently crosslinked elastomers and thermosetting polymers have been acknowledged as strategically important materials in industry, national defense and our daily life. Although the strong covalent crosslinks confer these conventional thermosets desirable properties, they also preclude repairing, reshaping, reprocessing and recycling, which has caused serious environmental pollution and resource wastage. By introducing bio-dynamic covalent bonds and adding reinforcing fillers, a novel green type of polymers that are potentially recyclable, reprocessable and sustainable has been developed. However, most of the reported bio-crosslinked polymers are still far from being extensively used in real-world applications due to the limited understanding of their processing-structure-property relationships. This research project aims to discover the fundamental principles that govern the mechanical and chemical properties of bio-based polymer composites, with the aid of multiscale computational modeling, data science (statistical analysis), and experimental validation. With quantified microstructure-property relations and unraveled deformation mechanisms, advanced bio-based reprocessable and mechanically robust polymer composites can be developed for wide applications, which will significantly mitigate the severe plastic pollution issue. The project includes an education and outreach plan to train diverse groups of next-generation of engineers: organizing workshops, seminar talks and local recycling center tours to K-12 students, providing high school students with summer internship opportunities, training undergraduate and graduate students the research skills of coding, writing and presenting. Particularly, research opportunities will be created for underrepresented students including physically disabled students. Through developing a novel multiscale framework that integrates density functional theory (DFT), all-atom molecular dynamics (AA-MD) and coarse-grained molecular dynamics (CG-MD), the goal of this project is to establish a fundamental understanding of the role of exchangeable bio-crosslinks in assisting the polymer composites strike their excellent balance among mechanical, functional, and reprocessing properties. The research objectives include: (i) seamlessly bridging DFT, AA-MD and CG-MD by force field calibration/optimization/parameterization; (ii) understanding the fracture mechanisms of two representatives: bio-based styrene-butadiene rubber (SBR) and bio-based epoxy vitrimer. The following knowledge gaps will be addressed: (1) the mechanisms of de-crosslinking/re-crosslinking during curing; (2) the advantages of bio-crosslinks over conventional linkages (e.g., S-S, C-S bonds); (3) the interfacial interactions between nanofiller and polymer; (4) the influence of reprocessing on structure and mechanical performance of reclaimed polymers; (5) microscale and mesoscale structure-property relations. The research outcomes will advance the knowledge of mechanics in bio-based polymer composites, as well the integrated multiscale framework can be extended to other amorphous materials, such as hierarchical biomaterials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.