Date of Award

Spring 2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Polymer Science and Engineering

Committee Chair

Jeffrey S. Wiggins

Committee Chair School

Polymer Science and Engineering

Committee Member 2

Robson F. Storey

Committee Member 2 School

Polymer Science and Engineering

Committee Member 3

Yoan C. Simon

Committee Member 3 School

Polymer Science and Engineering

Committee Member 4

Sergei I. Nazarenko

Committee Member 4 School

Polymer Science and Engineering

Committee Member 5

William L. Jarrett

Committee Member 5 School

Polymer Science and Engineering

Abstract

Epoxide amine matrices are widely utilized in aerospace carbon fiber reinforced polymer (CFRP) composites having engendered significant reductions in weight and fuel consumption. This dissertation focuses on the effect of constrained space during network formation on the matrix mechanics of these highly complex composite systems. Precipitation polymerization conditions are developed to prepare epoxide amine microparticles (EMs) based on tetraglycidyl-4,4’-methylenedianiline (TGDDM) and isophorone diamine (IPDA). Surface functionality of EMs is tuned via control of epoxide to reactive amine hydrogen ratio, where unreactive, amine- and epoxide-functional EMs are prepared. We demonstrate that EMs are polydisperse, but can be filtered, yielding low dispersity particle distributions. The influence of constrained space on matrix mechanics during cure was elucidated upon incorporation of EMs into the selfsame TGDDM/IPDA monomer formulation.

Microparticle synthesis is studied utilizing a library of epoxides, diamines and solvents in conjunction with computational techniques, establishing the factors influencing microparticle dispersity. Di-, tri-, and tetrafunctional epoxides are exploited to control oligomer structure from linear to branched architectures, leading to exponential increases in particle dispersity with increasing epoxide functionality. Improving solvent-monomer interactions and enhancing flexibility of diamine backbones served to decrease the dispersity of high functionality chemistries.

Incorporation of mono- and polydisperse microparticles decreases gelation time by 10-15% and degree of cure by up to 8%, independent of particle size. Ultimately, however, relaxation behavior of the gel, network homogeneity and thermomechanical properties remain unchanged upon microparticle incorporation. Despite this, networks exhibit an increase in Young’s modulus, 20% over the neat network, utilizing high dispersity particles. In contrast, low dispersity particles do not improve modulus, but impart greater fracture toughness (K1c) by introducing energy absorbing mechanisms, altering the fracture mechanics of the network.

Finally, reactive amine EMs are incorporated into CFRPs. As particle loading increases, matrix content and interlaminar spacing increase due to decreased gelation time. Consequently, moduli of the particle-modified composites decrease. However, a 1wt% loading improves tensile toughness of the composite by 40% with a 10% decrease in modulus. This research demonstrates a novel approach to prepare EM toughened CFRPs and serves as the foundation for the preparation of next generation aerospace composite materials.

ORCID ID

https://orcid.org/0000-0002-1335-775X

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