Date of Award

Fall 12-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Polymer Science and Engineering

Committee Chair

Sarah E. Morgan

Committee Chair School

Polymer Science and Engineering

Committee Member 2

Xiaodan Gu

Committee Member 2 School

Polymer Science and Engineering

Committee Member 3

Sergei I. Nazarenko

Committee Member 3 School

Polymer Science and Engineering

Committee Member 4

Derek L. Patton

Committee Member 4 School

Polymer Science and Engineering

Committee Member 5

Jeffrey S. Wiggins

Committee Member 5 School

Polymer Science and Engineering

Abstract

This dissertation focuses on evaluating the rheological characteristics of a variety of recyclable polymer matrices, which can compete with thermosets in a wide range of specialized applications. Studying the fundamental solid and melt-state viscoelastic properties and establishing structure-property-processing relationships is critical for the widespread adoption of these novel recyclable polymers in commercial applications. The first chapter provides an introductory overview of the different recyclable polymer matrices and their applications including high performance thermoplastics as thermoset replacements in high energy composite manufacture, multifunctional specialty thermoplastics for additive manufacturing and next generation, reprocessable covalent adaptable networks for self-healing applications. Furthermore, the important material rheological considerations for each of the intended applications is also discussed. In the second chapter, the melt blending two different types of POSS at low concentrations with a high performance thermoplastic, polyethersulfone (PES) is presented as an efficient processability enhancement strategy, which occurs without accompanying decreases in thermal and mechanical properties. The combined results indicate that the underlying mechanism driving the unique viscosity reduction is related to a decrease in chain entanglement density and an increase in free volume at PES processing temperatures. In the third chapter, the processability, rheological and crystalline properties of polyvinylidene fluoride (PVDF), a piezoelectric specialty thermoplastic, were studied as a function of melt blending with two different POSS chemicals, polymethylmethacrylate and POSS-PMMA copolymers were melt blended at low loading levels. All the filler types demonstrated an enhancement of PVDF melt processability but also hindered its iii crystallization. Further analysis revealed the crystallization-induced phase separation of the filler particles which broadened the crystal-amorphous interface. Each filler type displayed this phenomenon to a varying extent depending on the strength and nature of its interactions with PVDF. The fourth chapter reviews the critical thermal transitions and viscoelastic properties, and methods to characterize them for associative covalent adaptable networks or vitrimers. The understanding of fundamental concepts is extended to a novel diketoenamine-based vitrimer for which the thermal transitions are identified and the relation between them is interpreted with respect to processability using SAOS rheological analysis.

ORCID ID

https://orcid.org/0000-0001-7221-9333

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