Date of Award

Spring 5-2021

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. Sarah Morgan

Committee Member 3 School

Polymer Science and Engineering

Committee Member 4

Dr. Xiaodan Gu

Committee Member 4 School

Polymer Science and Engineering

Committee Member 5

Dr. Yoan Simon

Committee Member 5 School

Polymer Science and Engineering

Abstract

Atomic oxygen (AO) attacks polymer matrix composites (PMC’s) on the surfaces of spacecraft in low earth orbit (LEO) and threatens safe spacecraft operation and service life. Incorporating phenylphosphine oxide (PPO) groups into polymer chains offers a self-regenerating method of protection from AO but remains poorly understood. Herein, epoxies containing PPO groups were synthesized with increasing concentrations of phosphorus [P] from 0 to 8 wt % to investigate their AO resistance. Measurements confirmed the exposure of these materials to AO produces a passivation phosphate (POx) layer on the surface of the sample and the efficacy of the resultant layer was directly related to initial [P]. Furthermore, key insights into the relationship between initial [P], passivation layer surface topology, and polymer depth profiles were obtained. Crucially, results indicate that phosphine oxide epoxies’ (POEs) AO resistance can be readily tuned via synthetic incorporation of monomers with varying [P]. It was observed that PPO catalyzed the polymerization reaction between N,N,N’,N’-tetraglycidyl-4,4’-diaminodiphenylmethane (TGDDM) and 3,3’-diaminodiphenylsulphone (3,3-DDS). Herein, the reactivity of the novel 4,4-bisglycidylethertriphenylphosphine oxide (bGE-tPPO) was studied via differential scanning calorimetry (DSC), kinetic models, real-time Fourier-transform near-infrared spectroscopy (RT-FTNIR), and small amplitude oscillatory shear rheology. The epoxide-amine polymerization as catalyzed by bGE-tPPO was observed to undergo significant autocatalysis at high (β ≥ 4 °C∙min-1) heating rates. However, formulations with high concentrations of bGE-tPPO were shown to be safe and processable despite significant iii acceleration of the polymerization reaction and high initial viscosities through careful control of curing conditions.

Finally, 10 μm thin films of POEs were cured into aerospace grade PMCs to generate a low-cost, highly AO-resistant PMCs with minimal disruption to standard composite preparation processes. Measurements confirmed that POE-protected PMCs exhibited less than 0.05 % mass loss after exposure to an AO flux equivalent to approx. 8.56 ∙ 1021 atoms∙cm-2, equivalent to approximately 2.5 years in LEO. In contrast, unprotected PMCs exposed to a similar AO flux underwent extensive damage including approx. 5 % mass loss and total erosion of surface polymer matrix. This work demonstrates the stunning potential of POEs as a means towards AO-resistant polymer matrix composites.

ORCID ID

0000-0002-0850-6407

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