Improving Atomic Oxygen Resistance of Composite Materials for Flexible Deployable Structures in Space Applications

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

This study achieved a deeper understanding on the factors which affect the degradation mechanism of organic polymer composites under a simulated space environment. The effects of atomic oxygen (AO) on three commercial composite materials, based on two space-qualified epoxy resins are studied. Samples were exposed to a total fluence of 3.82 ×10^20atom/cm^2, equating to a period of 43 days in low Earth orbit (LEO). The flexural rigidity and modulus of all laminates displayed a reduction of 5-10% after the first exposure (equivalent to 20 days in orbit). Fourier transform infrared (FTIR) spectra, obtained during prolonged exposure to AO, were interpreted using principal component analysis (PCA) to explore the degradation mechanisms. The results indicated that the weak points of the structures were alkyl moieties, which is consistent with other researchers’ work on the mechanism of AO erosion. These results aided the design of new matrix resin systems for this application.
Based on the understanding, a new resin system was developed with various desired properties for space applications. The main component of the resin was polybenzoxazine, a cashew nut based monobenzoxazine was also added to decrease the viscosity of the resin system while the introduction of an acidic initiator (3,3’-thiodipropionic acid, TDA) decreased the cure temperature of the resin system. POSS has also been successfully incorporated into the resin system to further increase the AO resistance of the resin system. Samples underwent an ultrahigh AO fluence (2.69 ×10^21atom/cm^2, equating to a period of 300 days in low Earth orbit) for the consideration of long duration missions. Several baseline tests were carried out on the resin and the results indicated the addition of POSS decreased AO erosion yield by 69% compared with unmodified resin system and by 75% compared with the epoxy resin system used in commercial composite structures. Higher portion of POSS can further decrease the erosion yield in early stage, but in later stage the effect of POSS was similar SEM and FTIR results suggested that the protection mechanism of POSS functioned through the formation of a silicon-based layer on the surface of the sample in response to AO exposure, which shielded the resin below from AO erosion.
The new resin system also showed desired mechanical properties when used in composites. The mechanical properties of the new resin system based composites showed comparable results as the literature reported. Furthermore, with the addition of POSS, the flexural modulus of the composites was slightly increase (by 19%) while the mode Ⅰ and Ⅱ fracture toughness increased by 36%~62%. The results indicated that the newly designed AO resistant resin system can be used as a composite with promising mechanical properties.
Date of Award29 Sep 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SponsorsOxford Space Systems
SupervisorIan Hamerton (Supervisor) & Mark Schenk (Supervisor)

Keywords

  • Atomic oxygen
  • Composite materials
  • Polybenzoxazine
  • Low earth orbit
  • POSS
  • Resin system
  • Epoxy

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