CAREER: Pathways of Microplastics Creation: Multi-physics Study of Macroplastic Fragmentation, Foliation, and Fibration

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This Faculty Early Career Development (CAREER) grant supports research to understand the degradation mechanisms of macroplastics into microplastics under coupled effects of weathering and mechanical stresses. It is well-established that microplastics exist in our oceans in ever-increasing numbers and cause great ecological harm. Physical, mechanical, and chemical properties of macroplastics change during the degradation process and make it challenging to detect microplastics and estimate their lifetime in water. To address this challenge, it is critical to understand the formation mechanisms of microplastics and the rates at which they are produced. The objective of this research project is to discover the mechanics of degradation and develop predictive models which can estimate the fate of macroplastics. The outcome can help ocean environmental scientists and the manufacturing practices and recycling processes. The research activities will be complemented with a series of integrated educational activities to train the next generation of engineers and researchers in the multi-physics and mechanics of soft polymers through combinations of undergraduate and graduate students training and outreach to high-school students. The award will also be used to contribute to public knowledge infrastructure and create workshops for the polymer industry. Separate models exist for studying how polymers degrade due to two or three factors among mechanical loading, temperature, oxygen, salt-water, and UV irradiations. The principal emphasis of this project is on the nonlinear coupling effects of all these factors. Physics-based equations for degradation in microstructural properties will be established based on polymers' network statistics, chemistry kinetics, as well as stored and dissipative energies. The critical internal stress at which micro-cracks form in thin polymers will be determined using polymer statistics and conservation laws. A non-affine multiscale framework will be built upon the deformation and breakage in chains and crosslinks to predict heterogeneous damage initiation and propagation. A physics-guided machine learning algorithm will assist the development of the framework. The damage mechanisms, threshold, and transition from brittle to ductile under multi-physics conditions will be described. The particular questions to be answered include (1) effects of the microstructural morphology of macroplastics on the degradation process and the choice of a specific fracture pathway -- fragmentation, foliation, or fibration, (2) changes in mechanical properties due to thermo-chemo-UV internal stresses in soft polymeric materials, and (3) failure mechanisms in semi-crystalline and amorphous polymer under coupled conditions at different scales.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.