Date of Award
5-2024
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
School
Polymer Science and Engineering
Committee Chair
Dr. Jeffrey Wiggins
Committee Chair School
Polymer Science and Engineering
Committee Member 2
Dr. Derek Patton
Committee Member 2 School
Polymer Science and Engineering
Committee Member 3
Dr. Zhe Qiang
Committee Member 3 School
Polymer Science and Engineering
Committee Member 4
Dr. Sergei Nazarenko
Committee Member 4 School
Polymer Science and Engineering
Committee Member 5
Dr. James Rawlins
Committee Member 5 School
Polymer Science and Engineering
Abstract
Imine vitrimers have attracted significant attention for the design of recyclable composite matrices. However, reliance on solvent processing limits their practical application as thermoset replacements in existing composite manufacturing techniques. This research aims to overcome this limitation by utilizing orthogonal benzoxazine (BOX) polymerizations for the solvent-free synthesis of imine vitrimers. The dissertation examines the evolution in the molecular design of imine-containing benzoxazine (iBOX) monomers, explores the structure-property relationships of the resulting networks, and concludes with the production of dynamic matrix composites.
Structurally similar aldehyde-functional BOX monomers were prepared using various synthetic approaches to achieve high-purity crystalline monomers. The aldehyde-BOX monomers were subjected to melt-state reactions with diamines, investigating the influence of monomer structure on selective imine formation. An optimal monomer was identified, demonstrating efficient imine formation, suppressed side reactions, and homopolymerization into void-free networks.
A series of iBOX monomers were prepared with various linking diamines. Rheological studies demonstrated tunable monomer melt processability before gelation, which was vital for composite manufacturing. The thermal, mechanical, and dynamic exchange properties of the resulting networks were evaluated and correlated to the monomer structure. Recycling studies demonstrated that all networks could be thermally reprocessed and chemically degraded under various conditions.
Dynamic exchange kinetics were further explored by synthesizing monomers with systematically altered backbone segments of varying polarity and molecular weight. These studies provided fundamental insight into modulating Tg, exchange Ea, and Tv of the iBOX networks through molecular design.
An iBOX monomer was selected based on its rheological behavior and unidirectional carbon fiber prepreg was prepared through hot-melt filming. Condensate-free crosslinking resulted in high-quality CFRPs with controlled matrix content and minimized porosity. The dynamic characteristics of the iBOX matrix were showcased through welding, healing, and thermoforming of cured laminates. Chemical recycling highlighted full matrix removal and recovery of pristine carbon fibers. As a final demonstration, a CFRP I-beam structure was designed and manufactured using the iBOX prepreg. The structure exhibited an exceptional strength-to-weight ratio, holding over 9,600 lbf in flexural loading. These findings underscored the potential to design high-performance CFRPs with recyclable characteristics enabled by the iBOX matrix.
ORCID ID
orcid.org/0009-0006-9476-3130
Copyright
2024, Levi Hamernik
Recommended Citation
Hamernik, Levi, "Dynamic Imine-Benzoxazine Networks For Recyclable Composite Matrices" (2024). Dissertations. 2235.
https://aquila.usm.edu/dissertations/2235
Included in
Materials Chemistry Commons, Organic Chemistry Commons, Polymer and Organic Materials Commons, Polymer Chemistry Commons