Investigating the Chemical Recycling of Polyesters and Polycarbonates: the Factors that Control the Depolymerization Rate and the Formation of Nanoplastics

The increasing demand for synthetic polymers is not being met with a corresponding rise in recycling, with only 9% of plastics being recycled annually. Consequently, the management of polymer waste is unsustainable, as most polymers end up in landfills or are incinerated. This research project examines Polyethylene Terephthalate (PET), Polycarbonate (PC), and TritanTM from Eastman Chemical Company, aiming to make recycling processes more sustainable. The focus is on understanding chain structure evolution during depolymerization, the impact of functional groups on depolymerization rates, polymer solvent compatibility, polymer crystal size's influence on depolymerization kinetics, and imaging nanoplastics from environmental samples. It further seeks to utilize telechelics formed during depolymerization for repolymerization or to create value-added products, ultimately advancing sustainable polymer recycling and developing economically viable materials from polymer waste streams.

This project aims to depolymerize polymers into oligomers for next-generation materials. My first project (Chapter II) revealed that annealing PET before depolymerization increased crystallinity and altered crystal structure, enabling the production of desirable dihydroxy-terminated oligomers with limited post-depolymerization reactions. Chapter III demonstrated that diol/polymer compatibility directs the rate of heterogeneous phase depolymerization, although the carbonyl carbon's reactivity also plays a role. Improved solubility (e.g., bisphenol-A) enhances the transition to a homogeneous phase, while poorer solubility (e.g., ethylene glycol) inhibits it. Chapter IV examines how crystallinity and crystal size impact the depolymerization of PET, enabling isolation of telechelic oligomers. The final project discussed (Chapter V) explores visualizing microplastics and nanoplastics using transmission electron microscopes and investigating how solubility affects the shape of formed nanoplastics.