Development of Scalable and Sustainable Processes for Polymer Recycling, Upcycling, and Synthesis

Abstract

The circular economy is a concept often heard of in the context of the plastic waste crisis. Yet, chlorinated plastics, polyvinyl chloride (PVC) in specific, are often left out of the circularity conversation, despite PVC being the third most produced plastic worldwide. This dissertation discusses the challenges facing chlorinated plastics, but also the unique upcycling opportunities they provide. Inspired by the potential, this dissertation showcases new methods and processes contributing towards the circularity of PVC. Fractionation is a technique often used for lignin separation, but rarely used in plastics. Here, PVC is fractionated using solvent mixtures of incrementing PVC-dissolution performance. Using a weak solvent (acetone) - nonsolvent (methanol) mixture, low molecular weight PVC fraction can be obtained. These fractions show remarkable solubility in solvents previously unconsidered in PVC chemistry. This work illustrates this via homogenous catalytic hydrogenation of dehydrochlorinated PVC. Using this method to modify PVC yielded products with polyethylene-like characteristics, while maintaining PVC properties and solubility, a feat rarely achieved in PVC modification. The methods developed open the door for a wide range of PVC modification paths. This success inspired ways to enhance the yield of soluble low molecular weight chains from bulk PVC. Thus, a method for the depolymerization of PVC was developed. Ozonolysis, while an “ancient” process, was never deployed as an approach for PVC depolymerization, only as an analytical tool. In this work, a new safe and scalable procedure for the ozonolysis of PVC was developed, yielding PVC products that are around a third or fifth the molecular weight of the starting material. The products were readily soluble in weak PVC solvents like acetone, aspiring use in 3D printing and PVC chemistry. While these methods cover a diverse range of concepts, they mainly belong to a single side of the circular economy, the end-of-life management. This dissertation also touches on another side, production, albeit of a different class of monomer. Vinylimidazoles were long produced using hazardous, and in some cases expensive, techniques. The methods reported in this work were considerably “greener,” covering nine out of the 12 principles of green chemistry. In totality, this dissertation diversly approached the end-of-life management of one of the most popular polymers, PVC, and the green production of a class of monomers previously produced using dangerous techniques.