Date of Award

Fall 12-7-2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Polymer Science and Engineering

Committee Chair

Sarah Morgan

Committee Chair School

Polymer Science and Engineering

Committee Member 2

Derek Patton

Committee Member 2 School

Polymer Science and Engineering

Committee Member 3

Zhe Qiang

Committee Member 3 School

Polymer Science and Engineering

Committee Member 4

Jeffery Wiggins

Committee Member 4 School

Polymer Science and Engineering

Committee Member 5

J. Kent Newman

Abstract

The focus of this dissertation is to add fundamental knowledge regarding structure/property/processing relationships for two important functional polymers, chitosan and polyvinylidene fluoride (PVDF). Chitosan properties and interactions with common additives have proven difficult to study due to the natural variability in molecular weight and functionality of commercial samples. Isolation of these factors was accomplished through the creation of well-defined glycopolymer mimics of chitosan with specific functionality which were used to better understand interactions with graphene oxide (GO) additives. Polyvinylidene fluoride (PVDF) has been underutilized in additive manufacturing because it is difficult to achieve printed parts with adequate mechanical properties, and the piezoelectric b-phase orientation has to date been elusive in melt-processed samples without additional post-processing. Blends of PVDF with cyclopentyl-functionalized polyhedral oligomeric silsesquioxane (Cp-POSS) nanostructured additives and poly(methyl methacrylate) (PMMA) were utilized to improve Fused Filament Fabrication (FFF) printability and tailor crystallinity to achieve piezoelectric printed parts.

The first chapter provides an overview of the functional polymers and nanocomposites utilized in this work and highlights relevant literature for the subsequent chapters. In chapter two, the synthesis and characterization of a new monomer and chitosan mimic were performed. The mimics have similar antibacterial properties and cytotoxicity to chitosan, providing value in potential applications that require solubility in water. These were designed to simulate the glucosamine unit of chitosan and were utilized to study interactions with GO. The same series of GO additives was studied in drop cast chitosan films to determine impacts on properties. The nanometer GO improves both strength and toughness, while micron GO improved strength but not toughness. Chapter three highlights the development of new thermoplastic chitosan powders and nanocomposite powders that include GO. The impacts of preparation methods and plasticization were evaluated to define structure-processing relationships. The tensile properties of these new thermoplastic chitosan materials were evaluated, and the addition of glycerin improved the toughness while the addition of GO increases the strength but lowered the toughness. Chapter four is devoted to the development of PVDF materials that have improved FFF printability and increased b-phase crystallinity. Blending PVDF with PMMA and Cp-POSS improves the interlayer adhesion and dimensional stability of PVDF while retaining the desired crystallinity and piezoelectric performance. Finally, in chapter five, the major conclusions from this work are defined along with future work that would add further value and scientific knowledge.

Available for download on Wednesday, January 01, 2273

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