Doctoral Dissertations

Orcid ID

https://orcid.org/0000-0002-7070-3145

Date of Award

12-2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Mark D. Dadmun

Committee Members

Alexei Sokolov, Thanh Do, David Harper

Abstract

Recycling plastics is not an optimized process, as only 9% of plastic waste is repurposed each year. Products from recycling streams have diminished mechanical properties, which makes them fiscally undesirable. These diminished properties are due to plastic sorting limitations resulting in immiscible polymer mixtures, which phase separate in the melt during mechanical recycling. Compatibilizers can be added to the melt to stabilize the interface between immiscible polymer blends. While the important molecular-level interactions of effective compatibilizers for blends composed solely of amorphous polymers are well established, the equivalent molecular-level processes that are needed in blends that consist of semicrystalline homopolymers remain less understood. This dissertation focuses on understanding the dominating mechanisms that enable effective compatibilizers for immiscible blends containing a semicrystalline polymer component. The first system evaluated is an immiscible blend of amorphous polyvinyl chloride (PVC) and semicrystalline polyolefin elastomer (POE). Chapter II looks at the individual interactions between commercially available chlorinated polyethylene compatibilizers and each homopolymer. This study determined that semicrystalline compatibilizers that optimized entanglement with the semicrystalline phase showed the best improvement in interfacial adhesion and the most significant evidence of cocrystallization. Chapter III expanded on these results using synthesized dichlorinated cyclooctene/cyclooctene gradient copolymers as compatibilizers with varying monomer feed ratios and molecular weight. Chapter V uses dechlorinated PVC as a compatibilizer vii for PVC/POE systems. These materials exhibit similar trends to those previously observed but have improved interfacial adhesion due to increased miscibility with the PVC phase, facilitated by the presence of vinyl chlorine groups. Chapter IV examined a semicrystalline/semicrystalline polymer blend system composed of high-density polyethylene and isotactic polypropylene. These blends were compatibilized with ethylene-propylene rubbers and an ethylene/1-octene random copolymer. In these compatibilizers, only the ethylene component is crystalline, and improved overall mechanical properties were found by optimizing the miscibility and entanglement between the semicrystalline components. Overall, in blends containing a semicrystalline homopolymer, the compatibilizer will entangle between the phases based on the miscibility of the segments and block lengths. If these segments are crystalline, then a cocrystal between the compatibilizer and homopolymer can form at the entangled sites, anchoring the interface.

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