CAREER: Fast-Rate Manufacturing of Thermoplastic Polymer Composites with Tailored Microstructure and Performance

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This Faculty Early Career Development (CAREER) grant will support research that contributes to the development of fast-rate manufacturing of high-performance thermoplastic composites with enhanced properties, promoting the US manufacturing science and technology. High-performance thermoplastic composites are emerging in industries to replace metals as these composites offer light weighting, outstanding mechanical properties, chemical stability, and manufacturability within few minutes via thermoforming. However, in fast-rate processes with high cooling rates, there is not sufficient time for the polymer to form long chain orders (crystals) that in turn reduces the crystallinity level. High crystallinity is required for improved stiffness and strength; however, lower crystallinity is desirable to improve toughness. These competing properties can be optimized by control of the detailed structure of the polymer. This grant supports fundamental research that fills the knowledge gap needed to engineer the thermoplastic composite crystallinity during processing to achieve concurrently high stiffness, strength and toughness. Nanomaterials (NMs) are used to control the crystallinity without the use of hazardous solvents, promoting the scalability. The research accelerates the manufacturing of next generation of composites with reduced weight and increased strength and toughness that benefits the US economy and national security by equipping U.S. automotive, aerospace and marine industries with a scalable and fast-rate manufacturing technique. The interdisciplinary nature of this research provides unique opportunities to train the next generation of highly skilled engineers and scientists in STEM fields especially from women and underrepresented minority groups that further enhances the diversification of the US manufacturing workforce.Optimized composite mechanical properties achieved during fast-rate manufacturing of semicrystalline polymer composites require engineering the crystalline morphology. This research will enable alternative capabilities in tailoring the microstructure of semicrystalline composites at multiple length scales during composite processing. Nanomaterials consisting of cellulose nanocrystals-graphene nanoplatelets are used to synergistically reinforce and create a hierarchical crystalline architecture. This project will generate new information by bridging the knowledge gap in the evolution of crystalline-amorphous domains from molecular bonds and forces, their translation to interfacial and interlaminar properties, and their deformation under service load. The research uses in-operando X-ray scattering and in-situ microscopy complemented by density functional theory and molecular dynamics simulations to establish the molecular interactions-semicrystalline microstructure-property relationship. The research also addresses the damage transformation from molecular bonds dissociation to delamination.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.