Available at: https://digitalcommons.calpoly.edu/theses/3110
Date of Award
6-2025
Degree Name
MS in Polymers and Coatings
Department/Program
Chemistry & Biochemistry
College
College of Agriculture, Food, and Environmental Sciences
Advisor
Shanju Zhang
Advisor Department
Chemistry & Biochemistry
Advisor College
College of Agriculture, Food, and Environmental Sciences
Abstract
Plastics are ubiquitous in the production of consumer and industrial products; their chemical stability, low cost of production, and performance versatility make them the best option for many industries. Their inherent benefits, specifically durability, is the basis for the negative environmental impact of polymers. Improper containment of endof-life polymer products causes unintentional migration into the environment. The monomers for many common polymer types are also fossil fuel based further increasing the environmental impact of the plastic lifecycle. Recycling is a possible method of closing the loop of the plastic lifecycle. Currently most recycling is physical, thermally reprocessing used plastics into products of much lower quality. Chemical recycling fully depolymerizes used plastics into monomers that can be readily used to create new products without quality loss. Poly(ethylene terephthalate) is a polyester that accounts for approximately 10% of the global plastic supply and is a great candidate for chemical recycling as it susceptible to many types of degradation. Many chemical recycling methods use non-sustainable chemical reactions and catalysts that are successful in degrading the used plastics but fail to reach environmental impact goals necessary to be considered a green process. Glycolysis is a well-studied method of PET recycling that has low environmental impact but is too slow to be widely implemented. This reaction v produces bis(hydroxyethyl) terephthalate (BHET) that can be used to easily produce various polymer products. Ionic liquid (IL) based catalysts can be used to accelerate glycolysis considerably. In addition, they are considered green catalysts since they can be reused multiple times without losing catalytic ability. This study is focused on optimizing the chemical recycling of PET via glycolysis catalyzed by [BMIM]ZnCl. In addition, the impact of polymer morphology on chemical recycling will be evaluated by comparing the product yield and kinetics of degraded crystalline and amorphous PET. Plastic materials and degradation product testing included structural characterization, thermal property analysis, reaction kinetics calculations, and yield/material usage optimizations. Optimal conditions for >90% yield of BHET were found for both polymer morphologies. It was also observed that amorphous polymers are more susceptible to chemical recycling requiring a shorter time to degrade.